Modern Concept Science and Technology 10

296 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 297FACTS WITH REASONSIf a bicycle is at rest, a bicycle dynamo cannot produce current.If a bicycle is at rest, a bicycle dynamo cannot produce current because the magnet will not move and magnetic flux will not change. Bicycle DynamoA bicycle dynamo is a very simple dynamo in which a magnet is made to spin round near a fixed coil. Electromagnetic induction is the principle behind the generation of electricity in a bicycle dynamo. It converts mechanical energy into electrical energy. ConstructionThe permanent magnet, insulated solenoid, wheel and axle is an important part of the dynamo. The axle contains a permanent magnet. The magnet is placed inside the solenoid in a container. The solenoids are good conductors. The wheel is connected to the tyres of the bicycle. When the tyres rotate, the wheel along with the permanent rotates inside the conducting coil (solenoid). Change in the magnetic flux produces electric current. Working mechanism A dynamo is based on the principle of electromagnetic induction. When the cycle is moving, its tyre rotates the wheel of the dynamo. Then the magnet will rotate. The magnetic lines of force are intersected by the coil and an emf gets induced due to a change in magnetic flux. It results in an induced current and lights the bulb. The current is induced in the bicycle dynamo as long as there is motion in the tyre.FACTS WITH REASONSWhen Ashmita used brakes, the brightness of the bulb decreased which was powered by a bicycle dynamo. When Ashmita used brakes, the brightness of the bulb which was powered by a bicycle dynamo decreased because less emf was induced due to a decrease in magnetic flux due to a decrease in rate of rotation. ACTIVITY 6Take an electric motor. Connect the LED bulb to the wires. Rotate the turbine many times at different speeds and observe the brightness of the bulb. GeneratorAn electric generator is a device that converts mechanical energy into electric energy on the basis of electromagnetic induction. It is used to generate electricity on a large scale. It has a strong permanent magnet. When the turbine is rotated by an external force, the rotor fixed to the magnet will also A dynamo produces alternating current (AC) whereas a dry cell produces direct current (DC).MEMORY TIPSBicycle dynamoMagnetic polesAC voltageSlip ringsCarbon brushesWorking of AC generator

298 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 299rotate. As a result, current is induced in the coil due to the change in the magnetic flux linked to the coil. There are two types of generators, i.e. A.C. generator and D.C. generators. Structure of AC GeneratorSome important parts of an AC generator are armature, magnet, slip rings, carbon brushes etc. The container contains a very powerful electromagnet. The conducting coil called the armature is placed inside the magnetic field. The coil is allowed to rotate inside the magnetic field. The armature is made of a soft iron core. There are two slip rings, each at one end of the armature. The first slip ring collects current when the armature rotates the first half turn. The second slip rings collect current when the armature rotates another half-turn. The carbon brushes are attached with slip rings to collect electricity. Working mechanism of the AC generatorThe AC generators are designed to produce alternating current. They work in the following way. The conductor is placed inside the magnetic field and rotated 3000 times per minute with the help of flowing water. Then the conductor will cut the magnetic lines of force. There will be a change in magnetic flux and the current will be produced in the conductor. When the armature rotates a half-turn, the current is collected by the first slip ring. When the armature rotates another half-turn, the current changes direction and it is collected by the second slip ring. So, the direction of the induced current keeps changing. The carbon brushes are in contact with slip rings. They collect induced current from slip rings. Methods to increase the induced emf from dynamo and generatorThe magnitude of the induced emf from a generator and dynamo depends upon the strength of the magnet, number of turnings in the coil, rate of rotation and distance between the magnet and the coil. Therefore, we can increase the magnitude of induced emf by using very powerful magnets that can produce powerful magnetic fields, increasing the number of turns in the coil, increasing the rate of rotation and decreasing the distance between the coil and the magnet. Differences between an electric motor and generator.Electric motor Generator1. An electric motor converts electrical energy into mechanical energy.1. A generator converts mechanical energy into electrical energy.2. It is based on the motor effect. 2. It is based on the principle of electromagnetic induction.3. Current is supplied to the coil placed in a magnetic field by an external source.3. The coil is rotated in the magnetic field by an external source.Large-scale sources of energy in NepalNepal is a developing country. The population of Nepal is also growing continuously. The energy demand is increasing every day. To meet this demand Nepal is focusing on renewable sources of energy. Electricity is a suitable form of energy that can be used for lighting, running When current is passed through a generator, or dynamo, it becomes an electric motor. So, an electrical generator can be run \"backwards\" to form a motor. MEMORY TIPS

298 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 299machines, vehicles, electronic gadgets etc. So, the Nepal government is focusing on large-scale production of electricity. Hydroelectricity, thermal energy, solar energy and wind energy are better options for large-scale production of electricity. Nuclear energy, tidal energy and geothermal energy are not suitable for Nepal. 1. Hydro-powerHydro-power is the energy that comes from the force of moving water. It can be found in those areas where water flows at high speed from high ground to low ground. To generate hydroelectricity, water is collected in a dam. The collected water is passed through a tunnel. The force of water can be used to rotate turbines connected with the generator which produces electricity. The electricity produced from running water by rotating turbines is called hydroelectricity. It is a cheap and non-polluting fuel. It is a renewable source of energy. Nepal Electricity Authority published in 2022 AD that Nepal is producing 2200 MW of hydroelectricity by then. The Upper Arun project, Uttar Ganga and Dudh Koshi dam projects are proposed to produce new 3219 MW hydroelectricity. Hydroelectricity is the best option as a large source of electricity for Nepal because Nepal has a lot of water resources which can be used to make hydropower plants. Hydropower plants can produce huge amounts of clean, renewable hydroelectricity.Advantages of hydroelectricityi. Hydroelectricity does not cause air pollution.ii. It can be transmitted over long distances in extremely small interval of time.iii. It can be converted into different forms of energy like heat, light, etc. by passing through suitable devices.iv. Water used to generate hydroelectricity can be reused for other purposes like irrigation.v. It is cheaper in long term use though the installation cost of a hydro-power plant is very high.2. Wind EnergyThe energy obtained from the moving wind is called wind energy. This energy is a result of unequal heating of the earth surface and the atmosphere. It is one of the oldest and cleanest forms of energy. A large amount of energy can be produced from the windmill. It depends upon weather and location. technology of hydroelectricityWind farm

300 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 301Wind energy is used for grinding grain, pumping water, or generating electricity. The kinetic energy of wind rotates the turbines connected with the generators which generate electricity. Wind power plants or wind farms are a collection of many wind turbines to generate electricity. Wind energy is mostly used in windy places such as Manang but it is not a major source of electricity in Nepal.Applications of wind energyi. Wind energy is used to propel sailboats.ii. Wind energy rotates the turbines connected with generator to generate electricity.iii. It is used to pump water from well.iv. It is used to grind wheat and other grains in grinding mills.3. Solar energySolar energy is growing popular in Nepal because we have lots of sunny days. However, it is not yet a major source of electricity. 4. Thermal energy A thermal power station can use thermal energy to produce electricity. The main concept of thermal power stations is to use heat energy to convert water into steam and use the pressurized steam to rotate a steam turbine which will eventually produce electricity. Any source of heat can be used to convert water into pressurized steam. For example, fossil fuel, nuclear energy, geothermal energy, biofuel, solar energy, waste incineration, etc. The design of a thermal power plant varies based on the source of heat. A coal-powered thermal power station burns coal to generate electricity. The coal is pulverized and burned in a pulverized coal-fired boiler. The heat converts water into very hot steam. The pressurized fast-flowing steam is passed into the turbine. The turbine rotates to produce electricity.The thermal power plant is bad for the environment because it emits lots of greenhouse gases into the environment.487 MW of electricity is produced by thermal energy in Nepal according to Nepal Electricity Authority in 2022 AD.FACTS WITH REASONSThe thermal power plant is not suitable for Nepal.Thermal power plants are not suitable for Nepal because they need a vast quantity of coal which is not available in Nepal. ACTIVITY 7Discuss the probability of a thermal power plant in Nepal. Hydropower stations, wind turbines and thermal power plants use AC generators. MEMORY TIPS

300 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 301TransformerThe transmission of electricity over a long distance with the same potential difference is very difficult. Potential difference decreases when current is transferred for a long distance. Similarly, high voltage current cannot be used for the domestic purposes. At the hydro-power station or nuclear power plants, the electricity is first generated at a lower potential difference. It must be stepped up to a high voltage. Similarly, when electricity enters a building or home, the high voltage alternating current (AC) should be stepped down to a low voltage alternating current (AC). This increase and decrease of the voltage can be done with the help of a device called transformer. Thus, a transformer is a device that converts high voltage AC to low voltage AC and vice versa. Structure of a transformer The core, the primary coil and the secondary coil are the important parts of the transformer. The core of the transformer is made of soft iron core. Multiple thin iron plates are laminated one upon another using shellac to make a huge core. The core has two solenoids in it. They are the primary coil and the secondary coil. The primary coil is the solenoid that receives input alternating current. It changes into an electromagnet while working. The secondary coil is the solenoid in which flux changes and emf is induced. The step-up transformer and the stepdown transformer are constructed similarly. The only difference is the number of turnings in the primary coil and secondary coil. If the number of turns in the primary coil is more, it is a step-down transformer and if the number of turns in the secondary coil is more, it is a stepdown transformer. FACTS WITH REASONSThe core of a transformer is laminated, why?During lamination of the core of a transformer, the soft iron strips are separated from one another by the layers of insulator. Due to lamination of the core, production of eddy current in the core is reduced. It prevents the core from excessive heating as well as energy loss. So, the core of a transformer is laminated. Working PrincipleThe transformer is based on mutual induction. It has two coils, the primary coil and the secondary coil. Alternating current passes through the primary coil when it is connected to an AC source. The magnetic field due to AC in the primary coil changes in both magnitude and direction. These alternating poles of the magnetic field change the direction of magnetic lines of force linked with the secondary coil. Then there will be the change in magnetic flux and the TransformerA.C. input A.C. outputIron coreSecondaryCoilPrimary CoilMagnetic field in coreConstruction of transformer

302 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 303current will be induced in the secondary coil. The principle of mutual induction states that \"an emf gets induced in a coil by passing an alternating current in the neighbouring coil.\"FACTS WITH REASONSA transformer does not work with DC, why?Instead of AC, if DC is supplied in the primary coil, then the magnetic field do not change polarity. Due to this magnetic flux will not change in secondary coil. In such condition, current does not get induced from the two terminals of the secondary coil. So, transformer does not work with DC.A transformer cannot change the emf of a dry cell,why?A transformer cannot change the emf of a dry cell because dry cell produces only DC current. The DC do not change polarity, magnetic flux won't change and current won't be produced in secondary coil. So, a transformer cannot change the emf of a dry cell.Transformer FormulaThe relation among primary voltage (V1), primary turns (n1), secondary voltage (V2), and secondary turns (n2) in a transformer is called transformer formula. It is given as:Secondary voltage (V2)Primary voltage (V1) = Secondary turns (n2)Primary turns (n1)or,V2V1 = n2n1Types of TransformerThere are two types of transformers. They are step-up transformer and step-down transformer.a. Step-up transformerA transformer which is used to increase the voltage of alternating current AC is called a step-up transformer. In this transformer, the number of turns in the secondary coil is more than the primary coil, i.e., n2 > n1. It is used in a powerhouse. So, it has more secondary voltage than primary voltage, i.e. V2 > V1.Applicationsi. It is used to get high voltage to accelerate the electron beam in a cathode ray tube (CRT). ii. At the hydro-power station or nuclear power plants, the low voltage AC is stepped up to a high voltage using a step-up transformer. iii. In every microwave oven step-up transformer changes input voltage. iv. Inverter transformer converts low voltage from the battery into high voltage AC.v. It is also used in television sets, refrigerator, etc.OutputInputAC source220V11000VStep up transformer

302 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 303b. Step-down transformerA transformer which is used to decrease the voltage of alternating current AC is called a step-down transformer. In this transformer, the number of turns in the secondary coil is less than the primary coil, i.e., n1 > n2. So, it has more primary voltage than secondary voltage, i.e. V1 > V2.Applicationsi. In a distribution sub-station, a step-down transformer is used to lower the high voltage AC to low voltage AC for domestic use.ii. Battery chargers like cell phone charger have a step down transformer. It reduces high voltage (from 220 V) to low voltage (between 3 V to 9V)iii. It is also used in radios, cassette players, etc.Differences between Step-up transformer and Step-down transformerS.N. Step-up transformer S.N. Step-down transformer1. The output voltage is greater than the input voltage.1. The output voltage is lesser than the input voltage.2. The secondary coil has more turnings than the primary coil.2. The secondary coil has fewer turnings than the primary coil.3. It is used in hydropower stations and transmission sub-stations to increase AC voltage. 3. It is used in distribution sub-station to decrease high voltage down to 220 volts. Role of transformer to make AC available for domestic purposeThe transformer is a very important electrical device. It helps in the transmission of electricity from the power plants for domestic use. First of all the electricity produced in power plants such as hydropower plants, solar power plants, wind farms, nuclear power plants, thermal power plants etc. has low voltage. If current is transmitted at low voltage, we will lose a huge amount of current during transmission. The main power stations use a step-up transformer to increase the voltage of alternating current. For example, 400 kV (400,000 volts) is transmitted by Dhanusa transmission substation. Then the current passes through high voltage transmission lines to transmission sub-stations. Then the current will be transmitted to distribution substations. The load distribution substations have step-down transformers. The voltage of alternating current is now decreased to 220 to 240 volts in the distribution substations. Then AC is sent for domestic use. Again the step-down transformers are used to drop the voltage from 220 volts to suitable volts for mobile, laptop etc. A step-up transformer is used to run high-voltage machines such as electric vehicles, medical equipment and industrial machines. Solved Numerical 11.1The power supply to the primary coil of a transformer is 220 V and the turns in the primary coil are 2000. What must be the number of turns in the secondary coil to run a radio of 11 V from this transformer?Solution: Given,ACsourceInput11000V Output220VStep down transformer

304 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 305 Primary voltage (V1 ) = 220 V Primary turns ( n1) = 2000 Secondary voltage (V2 ) = 11 V Secondary turns ( n2) = ?According to the transformer formula, V2V1 = n2n1or,11220 = n22000or, n2 = 2000 × 11220 = 100Therefore, the number of turns in the secondary coil must be 100. Solved Numerical 11.2In a transformer, the ratio of secondary turns to primary turns is 4:3. Which type of transformer is it? Find the secondary voltage when the transformer is connected to a power supply of 220 V. Solution: Given,The ratio of secondary turns to primary turns (n2: n1) = 4:3This transformer has more turns in secondary coil. So, it is a step-up transformer.Primary voltage (V1) = 220 VSecondary voltage (V2) = ?According to the transformer formula, V2V1 = 43or,V2220 = 43or, V2 = 220 × 43 = 293.33 VTherefore, the secondary voltage is 293.33 V. Solved Numerical 11.3The coil of a transformer has primary turns double of secondary turns. Calculate the input voltage if 220V is generated by the secondary coil.Solution: Given,Let, the number of turns in secondary coil (n2) be xThen number of turns in primary coil (n1) is 2xInput voltage (V1) = ?Output voltage (V2) = 220V

304 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 305According to the transformer formula, V2V1 = n2n1or, V1n2 = V2n1or, V1 × x = 220 × 2xor, V1 = 440The input voltage (V1) = 440V.HOT SKILL HIGHER ORDER THINKING SKILL1. A ceiling fan cannot be operated if we use the current from a solar panel without using an inverter.Electricity from the solar panel is direct current but the ceiling fan needs alternating current to operate. Only the inverter can change DC into AC. So, a ceiling fan cannot be operated if we use the current from a solar panel without using an inverter.2. Alternating current would be useless without a transformer. Alternating current should have very high voltages during transmission to avoid power loss. It is sent for domestic uses at the voltage of 220 Volt from the distribution sub-station. Most electronic tools and gadgets operate at lower voltages. Therefore, the transformer is necessary to change AC to suitable voltages for transmission of AC, distribution of AC and operating machines, electrical gadgets etc. Therefore, without a transformer, AC will be useless for us. 3. Differentiate between a transformer and an electric motor. The differences between transformer and electric motors are:SN Transformer SN Electric motor 1 A transformer is designed to change the voltage of AC.1 An electric motor is designed to change electricity into kinetic energy.2 It cannot work with DC. 2 An electric motor can work with DC. 4. Ritika made a simple electric motor by using a coil, paper clips, a dry cell, and a permanent magnet as shown in the figure. How does it work? Explain. This electric motor works in the following way. A permanent magnet is kept above the battery. It is the first magnetic field in this experiment. A copper coil is placed just above the magnet in such a way that it can rotate if motion is produced. If we pass the current in this coil, in this setting, a new magnetic field will be produced around the coil. It is called the magnetic effect of current. Now, the first magnetic field and the new magnetic field will interact. They will pull or push each other. As a result, they will start to rotate. The motion and the rotation produced in that coil are called motor effects. 5. When electricity from the solar panel is directly supplied to the fridge, it won’t work. A fridge usually runs on AC. So, when electricity from the solar panel is directly supplied to the fridge, it won’t work because solar panels produce direct current.

306 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 3076. Who discovered the magnetic effect of electricity? If a current flowing in a conductor can produce a magnetic field around it, can a conductor placed in a magnetic field produce current? Under what condition is it possible for a conductor placed in a magnetic field to produce electricity? What happens if we supplied current in that conductor instead? What is this phenomenon called? Hans Christian Oersted discovered the magnetic effect of electricity. A current flowing in a conductor can indeed produce a magnetic field around it but a conductor placed in a magnetic field cannot produce electricity when it is at rest. However, if the conductor is in motion inside a magnetic field, a current will be induced. If we supply sufficient current in that conductor placed in a magnetic field, it will produce motion. This phenomenon is called the motor effect.7. Study the given diagram and answer the following questions.i. Name the device. The device shown in the above diagram is an electric motor. ii. What is the reason for the production of motion in the conductor? The conductor is inside a magnetic field. When current is passed in the conductor, another magnetic field is produced. Two magnetic fields repel each other and produce motion. iii. What is the name of the phenomenon that produces motion in the conductor of that device?The phenomenon that produces motion in the conductor of that device is called the motor effect. iv. What can be done to increase the rate of rotation? We can supply a higher voltage of electricity to increase the rate of rotation or use a powerful magnetic field. v. Which rule helps to find the direction of rotation of a conductor placed in a magnetic field?Fleming's left-hand rule helps to find the direction of rotation of a conductor placed in a magnetic field 8. Chargers of laptops and mobile phones have transformers in them. Mention the type of transformer they possess. Why do they have that transformer? The chargers of laptops and mobile phones have a step-down transformer in them. They have step-down transformer in them to lower down the AC voltage from 230 Volts to the required voltage. These devices do not operate at a higher voltage. 9. Nuhang doubled the speed of the bicycle. What will happen to the amount of electromagnetic force produced in the bicycle dynamo? According the Faraday’s laws of electromagnetic induction, the magnitude of the electromagnetic force (emf) is directly proportional to the rate of rotation. Therefore, if Nuhang has doubled the speed of the bicycle, the rate of rotation of the magnet of the bicycle dynamo will also be doubled. Then the rate of change of magnetic flux will also be doubled. Then the magnitude of the induced electromotive force will also be doubled. The brightness of the bulb will also be doubled.

306 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 30710. Even though the primary coil does not touch the secondary coil, the AC that enters the primary coil can be obtained from the secondary coil. How can a secondary coil supply current even if it is not connected to the primary coil? Explain. The secondary coil can give current even if it is not connected to the primary coil because electromagnetic induction occurs in the secondary coil. When the primary coil receives AC, it produces a magnetic field with alternating poles. So, the magnetic flux linkage occurs at the secondary coil. The magnetic flux changes in the secondary coil. Hence, current is produced in the secondary coil due to a change in magnetic flux. 4 STEPS EXERCISE EXERCISESTEP11. Multiple Choice Questions a. What is the motor effect?i. when current goes into the primary coil, it turns into a magnet whose pole changes and produces EMF in the secondary coilii. when alternating current goes into the magnetic field of the DC motor, the coil rotatesiii. when direct current goes into the magnetic field of the DC motor, the coil rotates iv. when current is passed into the solenoid, it produces a magnetic fieldb. Why does bicycle dynamo glow brighter if the bicycle runs faster?i. higher change in magnetic fluxii. slower change in magnetic flux iii. no change in magnetic flux iv. magnet grows powerful if the bicycle runs faster c. What kind of electricity has zero frequency?i. direct current ii. alternating current ii. induced current iv. lightning d. If we rotate the coil in all of these places at the same rate, where will obtain the highest amount of current?Less number of magnetic lines of force More number of magnetic lines of force Poles of a bar magnet A BThe middle portion of a bar magnet C Di. A ii. Biii. C iv. D

308 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 309e. Various effects that happen in the transformer are listed below. Which one is in the correct order?i. magnetic flux → magnetic flux linkage → magnetic effect of currentii. magnetic effect of current → magnetic flux linkage → magnetic flux change iii. magnetic flux linkage → magnetic effect of current → magnetic effect of currentiv. mutual induction → motor effect → electromagnetic induction f. What is the principle of B? A B rotates to produce current uses current to rotate spinning conducting coil inside a magnetic field i. magnetic effect of current ii. electromagnetic inductioniii. motor effect iv. mutual induction g. Observe the given statements and arguments and choose the best option.Statement: Hydroelectricity is one of the best large-scale sources of electricity for Nepal.Argument 1: I disagree! Coals and petroleum are the largest, cheapest and best sources of energy in Nepal. Argument 2: Well! I assume hydroelectricity is the best source of electricity because we have lots of fast-flowing slanted perennial rivers in our country.i. Statement and argument 2 are incorrect but argument 1 is correct.ii. Statement is wrong. Arguments 1 and 2 are correct. iii. Statement and argument 2 are correct. Argument 1 is incorrect. iv. Arguments 1 and 2 are incorrect. The statement is correct. h. Select the best option based on the information shown in the diagram. i. It is a motor. ii. It is a step-up transformer.iii. It is a step-down transformer.iv. It is an inverter. i. Which of the following electrical devices uses electromagnetic induction?i. waterpump, laptop charger, adapter ii. bicycle dynamo, AC generator, solar panel iii. drycell, photocell, battery iv. dynamo, transformer, generator j. If the number of primary turning is double that of secondary turning, calculate the output voltage if the device is connected to 220 volts mains.i. 220 volts ii. 100 volts iii. 440 volts iv. 110 volts a. iii b. i c. i d. ii e. ii f. iii g. iii h. iii i. iv j. ivAns of MCQ

308 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 309STEP22. Very short questions a. What is the name of the device shown below?b. What is DC? c. When the terminals of the battery, connected to the DC motors were reversed, the motor rotated in the opposite direction. Why?d. If a magnetic compass is placed near position A, which pole of its needle will face position A? Which pole of the needle of the magnetic compass will be pulled if the direction of the current is reversed? e. There is a solenoid connected to the galvanometer. A bar magnet is pushed into the solenoid. Now the solenoid also acts as a magnet. Why? f. What is meant by the frequency of electricity being 50 Hz in Nepal?g. Name an instrument based on the magnetic effect of current. h. Why does a magnetic needle deflect near the current-carrying conductor? i. The current time graph of DC is parallel to the x-axis. What does it mean?STEP33. Short questions a. Why the current produced from a solar panel cannot run a refrigerator?b. Write two differences between an AC generator and an electric motor.c. How can a drop in the voltage be prevented while transmitting electricity over long distances?d. Write down any two methods to increase emf produced from the given device.e. 'Use of alternating current would be limited in absence of transformer'. Justify this statement.f. When the battery connected to the electric motor was replaced with an LED bulb and the armature was forcefully rotated, the bulb glowed. The electric motor is not a source it cannot glow the bulb. Ram is surprised. Clarify what’s happening in this experiment for himg. An alternating current of 220 V is available in our home. If we have to light a bulb of 6V, which type of transformer should we use? Show it in a figure. h. A dynamo is connected to Sushma’s bicycle. The bulb connected to her cycle glows with the help of the dynamo. The brightness of the bulb increases when she paddles the bicycle faster. Explain.

310 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 311STEP44. Long questions a. Describe the structure of the dynamo. Draw its well-labelled diagram.b. Observe the given diagram and answer the following questions.i. Which principle is being tested in the above experiment? ii. When the magnet is dropped through the coil, the current is induced and deflection is observed in the needle of the machine. What does it mean? iii. If the magnet is at rest inside the coil, current will not be produced. Why? iv. What can we do to deflect the needle of the galvanometer wider?c. Describe the working mechanism of an electric motor and draw its schematic diagram.d. A transformer is shown in the figure. i. Label the parts A and B.ii. Which type of transformer is it?iii. The use of alternating current (AC) is limited without a transformer.' Justify it. 5. Numerical i. The p.d. of the power supply to the primary coil of a transformer is 220 V and the turns in the primary coil are 2000. What must be the number of turns in the secondary coil to run a radio of 11 V from the transformer? [Ans: 100 turns] ii. A transformer has 600 turns in the primary coil and 1200 turns in the secondary coil. The potential difference across the primary coil is 110 V. What is the potential difference induced across the secondary coil? [Ans: 220 V]iii. The number of turns in the primary coil of a certain transformer is 440 times more than that in the secondary coil. Calculate the input voltage in the primary coil if the e.m.f. generated in the secondary coil is 220 V. [ Ans: 96800 V]iv. In a transformer, the ratio of the secondary turns to primary turns is 2:3. Which type of transformer is it? Find the secondary voltage when the transformer is connected to a power supply of 220 V. [Ans: step down, 146.667 V]♦♦♦

310 e LectRicity and MagnetisM Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 311Key terms and terminologies of the unit1. Universe : The group of everything that exists such as earth, planets, satellites, dwarf planets, nebula, black holes, galaxies and other celestial objects is called the universe. 2. Universe Science : The branch of science in which we study about past, present and future of the universe is called universe science (cosmology). 3. Astronomy : The branch of science that studies about the universe is called astronomy. 4. Observable universe : The part of the universe that is visible from the Earth is called the observable universe. 5. Big Bang theory : The Big Bang theory states that the universe originated due to the big explosion of the highly dense, extremely hot and highly concentrated primordial atom. 6. Hubble’s law : According to Hubble’s law, the velocity due to which the galaxies are moving apart is directly proportional to the distance between them. 7. Mean density of the universe: The ratio of the mass of the universe to the volume of the universe is called the mean density of the universe.8. Critical density : The mean density of the universe that can produce sufficient gravitation to stop the expansion of the universe in the distant future is called critical density. Sequence of Curriculum Issued by CDC Importance of gravitation in the universe (existence of satellites, planets, stars, and galaxies in space) Origin of the universe based on the big bang Conclusion of Hubble’s observation of the motion of the heavenly objects  Possible fate of the universe, based on gravitation (open universe, close universe and flat universe)UNITUniverse12Estimated teaching periods Theory Practical4 1Binil Aryal, born in 1969 in Saptari District, Nepal, is a distinguished Nepali physicist and dean of Tribhuvan University's Institute of Science and Technology. Educated at Innsbruck University, Aryal's research in astrophysics, particularly focusing on galaxy orientation and evolution, has significantly enhanced our understanding of the universe. His work on galaxy angular momentum and interstellar medium shaping mechanisms has advanced astrophysics, enriching Nepal's scientific community and inspiring students and researchers. Binil Aryal About the Nepalese Scientist

312 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 3139. Close universe : The universe in which the force of expansion becomes zero earlier than the gravitation, and galaxies come back to a single point again is called a close universe. 10. Big crunch : The process in which every celestial object will be brought together and crushed into the singularity due to stronger gravitation is called a big crunch. 11. Open universe : The universe in which the gravitation becomes zero earlier than the force of expansion and the galaxies keep expanding forever is called an open universe. 12. Flat universe : A universe in which gravitation and force of expansion become zero at the same time and the gravitation can stop expansion just right after billions of years is called a flat universe. IntroductionThe group of everything that exists such as earth, planets, satellites, dwarf planets, nebula, black holes, galaxies and other celestial objects is called the universe. All of the celestial objects exist as they are because of mutual gravitation. Many curious people want to reveal the secrets of the universe. They research the universe. They are called astronomers, cosmologists, astrophysicists etc. The branch of science in which we study about past, present and future of the universe is called universe science. It is also called cosmology. The branch of science that studies about the universe is called astronomy. The laws and principles of astronomical objects, processes and their physical nature are studied under astrophysics. The part of the universe that is visible from the Earth is called the observable universe. Astronomers observe the observable universe during the night with the help of telescopes. They observe the distance galaxies, search for habitable planets, look at meteors and try to understand the formation of planets, the formation of stars, black holes, the shape of the universe and the future of the universe. There are many theories regarding the origin of the universe. However, the most popular one is the Big Bang theory, which focuses on the concept that the universe came to be from the explosion of a primaeval atom. Edwin Hubble is another unforgettable person in the field of astronomy. He is renowned for discovering the fact that the universe is expanding. The universe contains many objects. The gravitation is directly proportional to the mass of the objects. The object with greater mass can produce greater gravitation. Gravitation is a pulling force. The gravitation is the key factor that determines the fate of the universe. Importance of gravitation in the universei. Formation of star The gravitation shrinks the nebula into a hot ball of gas. If gravitation grows further, the fusion reaction will start in the hot ball of gas and it will change into the star. The sun is a star. It probably formed from a nebula. The gravitation compressed the nebula into a hot ball of gas, which later changed into the sun.Fig: nebula

312 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 313ii. Formation of the solar system The sun has a lot of mass. It produces sufficient gravity to pull planets, dwarf planets and comets around it. The mutual gravitation among the sun, planets, dwarf planets and satellites has given birth to the stable system called the solar system. We live in the earth. Earth is the third planet from the sun in the solar system. It has one moon. The gravitation between the earth and the moon keeps them locked to each other. There are 7 more planets besides the Earth. There are dwarf planets, asteroids, comets and satellites. Together, they are called solar systems. The planets and satellites do not collide because their mutual gravitation has already produced a fixed orbit where they rotate around the sun. The gravitational force helps planets and satellites to align and stay properly in their orbit, to avoid collision. The gravitation makes satellites revolve around planets, planets revolve around the sun and the sun revolves around the centre of the galaxy. iii. Formation of the galaxyThere are billions of stars in the galaxy. A galaxy is a megastructure formed when billions of stars, dust and nebula form a cluster due to their mutual gravitation. A galaxy contains solar systems, stars, black holes and nebula. The Milky Way galaxy is our home galaxy. Our earth lies in it. The Milky Way galaxy is a spiral galaxy. It has six arms and a central disk. The central part of the galaxy has a massive black hole, which produces tremendous gravitation that attracts all stars around it. The Milky Way galaxy is very big. Its diameter is 100,000 light years. Our solar system is 30,000 light-years far away from the centre of the galaxy. iv. Determine the fate of the universeThe galaxies are moving away from each other due to the force of expansion from big bang but the gravitation pulls each of them back. So, the fate of the universe could be an open universe, a close universe or a flat universe based on the magnitude of gravitation. FACTS WITH REASONSThe eight planets of the solar system are aligned in their orbit, rotate in their axis and revolve around the sun.The eight planets of the solar system are aligned in their orbit, rotate in their axis and revolve around the sun because of the mutual force of attraction called gravitation among the sun, the planets and other celestial objects within the solar system. Fig: solar systemFig: milky way galaxyIn the universe, there are some gigantic celestial bodies, with tremendous mass that can produce infinite gravity where as some objects are too tiny with almost negligible mass. MEMORY TIPS

314 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 315ACTIVITY 1Make a model to show the orbit of the Earth around the sun and the moon around the earth. Big bang theory The Big Bang theory states that the universe originated due to the big explosion of the highly dense, extremely hot and highly concentrated primordial atom. It suggests that the universe was extremely dense and hot in the beginning. Later it exploded into the new universe as we know it today. The Big Bang gave birth to strong nuclear force, weak nuclear force, electrostatic force and gravitational force. It gave birth to all these matters such as planets, nebula, galaxies and other heavenly objects present in the universe. First of all hydrogen, the simplest of all elements was formed. The gravitation changed them into the nebula, which compressed and changed into the star. Billions of stars were pulled together to form galaxies. All these galaxies, clusters, planets and other heavenly objects gained motion and centrifugal force through the big bang. Due to this centrifugal force, the galaxies are moving far away from each other. Even the space between each galaxy is also increasing. It means the galaxies are not simply moving away from each other but the space between them is also expanding. This fact leads to the hypothesis that the universe is actually expanding. So, the expansion must have begun from a very narrow, compact and dense place or object to ultimately form the universe as we know it today. This hypothesis is called the Big Bang theory. George Lemaitre proposed the Big Bang theory. The Big Bang is the most accepted theory of the origin of the universe because the expansion of the universe can actually be observed. Hubble’s law also supports this theory. Even though the universe is expanding, the rate of expansion is lesser than before because of the gravitation. Gravitation is centripetal force. It is produced by objects having mass such as black holes, planets and galaxies. It slows down the motion of galaxies by pulling them inward. It helps to slow down the expansion. The tug of war between centrifugal force, the expansion from the Big Bang and the centripetal force, the gravitation due to the average density of the universe determines the fate of the universe. The results of the Big Bang arei. It gave birth to the universe. ii. It gave birth to space, time, energy and matter such as celestial objects. iii. It gave birth to four major forces in the universe. iv. It gave centrifugal force to the galaxies that made the universe expand.FACTS WITH REASONSWhy did the Big Bang occur?The Big Bang occur due to excessive force, excessive pressure and very high temperature in the primaeval atom. Fig: big bang

314 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 315ACTIVITY 2Prepare a 2-minute audio-visual material to explain the Big Bang to your classmates. Hubble’s study Edwin Hubble is an American astronomer. He is the first person to discover that there is another galaxy besides our Milky Way galaxy. He discovered the spiral galaxy Andromeda. Later he discovered many other galaxies which were mistaken as clouds of dust and gases. Later he started to use a 100-inch Hooker telescope on Mount Wilson in California to measure the distance and velocities of the galaxies from our galaxy. If the galaxies are moving away from us the light coming to us from them appears to be shifted to longer wavelengths (toward red colour) in the spectrum. It is called redshift. In 1929 AD he noticed that every other galaxies around us were moving farther away from us by looking at redshift. He observed that rays of light coming from every galaxy from every direction are moving toward the red colour in the spectrum. It suggests that the universe is expanding. He noticed that the galaxies that were farther away from us looked smaller and the galaxies that were nearer to us looked bigger. He noticed that the galaxies that are farther from our galaxies have greater relative velocity than the galaxies that are nearer to our galaxy. ACTIVITY 3Take a big balloon and write HAPPY BIRTHDAY in it. Movement of galaxies far away from each other can be explain by the movement of letters of the word ‘Happy birthday’ written in a balloon. When we blow air into the balloon the balloon expands and becomes bigger. During that moment every letter of the word ‘HAPPY BIRTHDAY’ written in the balloon will move far from each other. The gap between letters H and P will increase less because they were already near and there is less room for expansion. The gap between letters H and Y will increase more because they are already far from each other. There was more room for expansion. So, the letter Y will move away faster from the letter H than the letter P. From the perspective of the letter R, the letter I as well as the letter T moves far away farther from it but in opposite directions when the balloon expands. The galaxies around the Earth are also moving away from Earth similar to the situations as explained above. Hence, the only logical conclusion is the universe must be expanding. In addition to this, if the universe is expanding at the moment, it must have started from a point or a very small but dense universe. This statement is similar to the Big Bang theory. Hence Hubble’s law supports the Big Bang theory. Hubble’s law He tried to find the relation between the distance between the galaxies from us and their receding velocity. He plotted in the graph as shown in the picture given below. From this graph, he obtained the relation V = Hd. In this equation V means the velocity at

316 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 317which the galaxies move away from each other, H means Hubble’s constant and the ‘d’ means the distance between galaxies. The value of Hubble’s constant is 73km/s/Mpc. It means if there are two galaxies in space and the second one is 1 megaparsec distance farther than the first one, then the second one (farther one) has more velocity than the first one by 73km/s. If the first galaxy is moving away from us at the velocity of ‘x km/s’ then the second one will be moving away from us at the velocity of ‘x + 73’ km/s. Simply, if the distance between two galaxies is 1 megaparsec then their relative velocity will be 73 km/s. They separate from each other at a velocity of 73 km/s. The Hubble’s equation is also called Hubble’s law. According to Hubble’s law, the velocity due to which the galaxies are moving apart is directly proportional to the distance between them. Hubble’s equation can calculate receding velocity (the velocity at which galaxies are moving away from each other).FACTS WITH REASONSThe galaxies in the western sky are moving farther away toward the west and the galaxies in the eastern sky are moving farther away toward the east. Does this mean Earth is the centre of the universe and everything is moving away from it or there is another reason? Justify. Yes! As observed, the galaxies in the western sky are moving farther away toward the west and the galaxies in the eastern sky are moving farther away toward the east. But ! this does not mean Earth is the centre of the universe and everything is moving away from it. There is another reason which is the universe itself is expanding at every place in every direction without an actual centre.ACTIVITY 4Observe the given picture taken by Hubble’s telescope. Are all of them stars or is there a chance that some of those are not a star but a galaxy very far? Discuss. Why do some of them appear smaller and some of them appear bigger? Discuss. Fig: the pictures of space taken from Hubble’s telescopeACTIVITY 5Take a balloon in which some words are written. For example, let’s say Happy Birthday is written in the balloon. Inflate the balloon and observe how the distance between letters increases. Make a report. The fate of the universe Gravitation is responsible for slowing down the velocity of accelerating galaxies. The size and shape of the universe depend upon how much the velocity of the galaxies is reduced by gravitation. Fig: the relation between velocity and distance in Hubble's studyThe H in Hubble’s law is the constant of proportionality which is called Hubble’s constant. MEMORY TIPSThe fate of the universe depends upon gravitation. The gravitation depends upon the mass of the universe and the volume of the universe. It means the gravitation depends upon the density of the universe. MEMORY TIPS

316 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 317For example, if gravitation can actually stop the motion of galaxies, the universe will be flat. If gravitation is way too strong, it can stop galaxies and condense them back to form close universe. If gravitation is weaker than the force of expansion, galaxies keep accelerating and form an open universe. Therefore, gravitation is a very important factor in determining the fate of the universe. The gravitation is produced from the mass of the galaxies that exist in the universe. The ratio of the mass of the universe to the volume of the universe is called the mean density of the universe. The mean density of the universe that can produce sufficient gravitation to stop the expansion of the universe in the distant future is called critical density. Based on the mean density and critical density, the universe can meet three different fates. They are the open universe, the close universe and the flat universe. Close universe If the mean density of the universe is more than the critical density a close universe will be formed. In this condition, the universe contracts continuously. In this model of the universe, the gravitational force of the universe is stronger than the force of expansion. Therefore, the universe in which the force of expansion becomes zero earlier than the gravitation, and galaxies come back to a single point again is called a close universe. Some distinct features of the close universe are:i. The mean density of the universe is greater than the critical density.ii. The gravitation produced by the mean density is strong enough to stop the motion of galaxies and pull them inward.iii. The volume of the universe keeps decreasing after the motion of galaxies is stopped.iv. The expansion of the galaxies becomes zero earlier than the gravitation. The close universe will end up in a big crunch. The process in which every celestial object will be brought together and crushed into the singularity due to stronger gravitation is called a big crunch. The new Big Bang can start again from this singularity. The life cycle of the close universe continues when the Big Bang and Big Crunch come alternately. It is commonly called an oscillating universe. ACTIVITY 6Will the gravitation of one heavenly object affect the other heavenly object after billions of years in an open universe? Discuss. The density of the universe as we know it today is simply the estimated data based on the ratio of total mass visible within the visible universe to the volume of the visible universe. It's not the actual density of the universe.MEMORY TIPSIf the gravitation is non-zero when the force of expansion is already zero, the universe will start to shrink and collapse into itself. Such universes are spherical. MEMORY TIPSFig: close universeFig: open universeFig: flat universe

318 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 319Open universeIf the mean density of the universe is lesser than critical density then an open universe will be formed. In this condition, the universe expands continuously. In this universe, the gravitational force of the universe is weaker than the force of expansion. Therefore, the universe in which the gravitation becomes zero earlier than the force of expansion and the galaxies keep expanding forever is called an open universe. Some distinct features of the open universe are:i. This universe expands continuously. ii. The mean density of the universe is lesser than the critical density of the universe.iii. Centripetal force from gravitation produced by the masses exceeds centrifugal force from Big Bang expansion. iv. The gravitation becomes zero before the motion of galaxies. The open universe is likely to end in a big freeze. It means every heavenly object in this universe will travel so far from each other that every celestial object will be alone in the universe. In the distant future, the gravitation from one heavenly object will never affect another. No work can be done in this universe. Heat won’t transfer. The entire universe will be in a big freeze and die. FACTS WITH REASONSThe distance between the sun and the earth is relatively constant, even though the universe is expanding. The distance between the sun and the earth is relatively constant, even though the universe is expanding because the gravitation between the sun and the earth is strong enough to hold them together, resist the force of expansion and prevent separation. ACTIVITY 7Make a 3D model of the three models of universe. Flat universe If the mean density of the universe is equal to the critical density a flat universe will be formed. In this condition the universe neither expands nor contracts. In this universe, the gravitational force equals the force of expansion. Therefore, a universe in which gravitation and force of expansion become zero at the same time and the gravitation can stop expansion just right after billions of years is called a flat universe. Some distinct features of the close universe are:i. The mean density of the universe is equal to the critical density.ii. The gravitation produced by the mean density is strong enough to stop the motion of galaxies just right.If the centripetal force from the gravitation produced by the mean density of the open universe cannot hold the expansion of the universe, every celestial object will move away from each other forever. Expansion never stops. MEMORY TIPSAn open universe can only be hypothesized if the mean density is less than the critical density. MEMORY TIPS

318 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 319iii. The volume of the universe stays constant after the motion of galaxies is stopped.iv. The expansion of the galaxies and the gravitation become zero at the same time. The flat universe will end up in a big freeze similar to the open universe but very slowly. It is the most stable form of the universe. FACTS WITH REASONSCelestial bodies of the flat universe will not be affected by mutual gravitational force after billions of years. Celestial bodies of the flat universe will not be affected by mutual gravitational force after billions of years because the gravitation is not able to stop the expansion at this moment, expansion will be stopped after billions of years and every object will be already infinitely far from each other. The heavenly objects will be so far from each other that the gravitation between them will be zero. Graphical representation of types of universeThe graphical representation of the three models of the universe is shown below. OpenFlatCloseomega pointalpha pointRadius of the Universenow timeFig: Types of universeFACTS WITH REASONSIf the distance between two galaxies increases, the rate of expansion between them increases. If the distance between two galaxies increases, the rate of expansion between them increases because the universe is expanding at every single point in every single direction, so there is more room for expansion between two objects if they are far. ACTIVITY 8Discuss your opinion on which model of the universe is most stable and why.

320 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 321HOT SKILL HIGHER ORDER THINKING SKILL1. Gravitation forms galaxies.Gravitation brings matter together. The stars are heavenly objects with a tremendous quantity of mass. So, the stars can pull each other and stay as a cluster. Sometimes a dying massive star can change into a black hole. Black holes produce enough gravitation to attract stars around them. As a result, billions of stars stay together. Such a cluster of billions of stars is called a galaxy. Hence, we can conclude that gravitation can form galaxies. 2. What is the conclusion of the observation of Edwin Hubble? Edwin Hubble’s observation of surrounding galaxies concludes that the galaxies farther from the Earth move away faster from us than the galaxies that are closer to the Earth. It means the universe is expanding. 3. Compare between the flat universe and the close universe.The comparison between the flat universe and the close universe are listed below:SN Flat universe SN Close universe 1 The critical density of the universe is equal to the mean density of the universe. 1 The critical density of the close universe is less than the mean density of the universe. 2 The centripetal force produced by gravitation balances centrifugal force from expansion just right.2 The centripetal force produced by gravitation is more than centrifugal force from expansion forces. 3 It will die in a big freeze. 3 It will die in a big crunch. 4. If a galaxy moves away farther from us, it will separate away faster than before. It accelerates. If a galaxy moves away farther from us, it will separate away faster than before. It accelerates because the universe itself is expanding. So, if the galaxies are farther from each other, there is more room between them where expansion can occur. Therefore, if galaxies are farther from each other, more expansion occurs between them. Hence, it appears that they are moving with faster velocity when they are farther from us. According to Hubble’s law, if the distance between two separating bodies is 1 megaparsec its velocity will increase by 73 km/s.5. In your opinion, what might be the future of the universe? State your opinion. The universe is probably flat based on the observations made today. As we can see the universe is expanding, however, there is sufficient mass within the observable universe. Cosmologists, who study the past, present and future of the universe believe that this mass present in the universe is probably able to produce sufficient gravity to stop expansion just right. The astrophysicists believe that the mean density of the current universe is equal to the critical density. So, the universe should be flat. However, nothing can be sure. The earth also looks flat, if we observe our surroundings only. So, the universe could also be close if the average density is more than the critical density or it could also be open if the average density is less than the critical density. 6. Multiple satellites revolve around Jupiter but they do not collide. Multiple satellites revolve around Jupiter but they do not collide because they move in their fixed orbit. Each of them including the planet has its own gravity. The mutual gravitation between them has forced

320 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 321them to revolve around the planet in a fixed orbit at a uniform velocity. They already have removed obstacles from their path too. Hence, they do not collide. 7. Why don’t planets collide while orbiting around the sun?The planets do not collide even though they are orbiting around the sun because they have their fixed orbit. They have already cleared other obstacles in their path.8. Celestial bodies of the galaxy continue to remain in their own place despite the universe expanding.Celestial bodies of the galaxy continue to remain in their own place despite the expansion of the universe because of mutual gravitation among each other and inertia of motion. The mutual gravitation among these celestial objects is strong enough to hold them together against the force of expansion. 9. Even though the universe is expanding, the galaxy does not expand. Even though the universe is obviously expanding the solar system does not expand. It is because the gravitational attraction between the stars and the black hole is strong enough to hold itself together. They act as a single unit in the space. So, they do not expand. 10. Importance of gravitation on the positioning of heavenly bodies in the universe. Gravitation plays a very important role in the positioning of heavenly bodies in the universe. For example:i. The gravitation between the gases keeps them together within a nebula.ii. The gravitation between stars keeps them together within the galaxies. iii. The gravitation between galaxies and their black holes gives shape to galaxies.iv. The mutual gravitation between the sun and planets keeps them in their respective orbits. v. The moon does not leave Earth because of gravitation between the earth and the moon. 4 STEPS EXERCISE EXERCISESTEP11. Multiple Choice Questions a. What helps in the alignment of planets and satellites in their orbits?i. sun ii. gravitation iii. planets iv. elliptical orbits b. What’s the conclusion of Hubble’s observation?i. galaxies far away are red ii. galaxies travel faster iii. universe is expanding iv. there are many galaxies around us c. Laxmi found that both types of universes, universe A and universe B have a mean density which is not equal to critical density. She also noticed that universe A cannot expand forever. Whereas universe B expands forever. Based on this information. She made the following statements. Which one is true? i. Gravitation of one celestial object does not affect another one in the distant future in universe A as well as universe B.

322 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 323ii. Gravitation of universe A becomes zero earlier than the force of expansion. Whereas the gravitation of universe B becomes zero later than the force of expansion. iii. Every object of the universe A will come together and change into a single object. Whereas every object of universe B will be so far from each other that they will be alone in the universe.iv. Universe A is called an observable universe. Whereas universe B is described by Hubble’s observation only. d. Which of the following represents Hubble’s observation? Galaxies near the Earth Galaxies far from Earth Less receding velocity A BMore receding velocity C D i. A and D ii. B and C iii. A and C iv. B and D e. Which of the following is the correct order?i. primaeval atom → big bang → mass → gravitation ii. big bang → Primaeval atom → mass → gravitationiii. gravitation → mass → primaeval atom → big bang iv. atom → big bang → gravitation → mass f. What are the conditions required for a universe to be open? i. critical density less than mean density, centripetal force exceeds the centrifugal force ii. critical density greater than mean density, centripetal force does not exceed centrifugal force iii. critical density less than mean density, centripetal force does not exceed centrifugal force iv. critical density equals mean density, centripetal force equals centrifugal force g. Why does every celestial object come to rest in a flat universe?i. critical density less than mean density, centripetal force exceeds the centrifugal force ii. critical density greater than mean density, centripetal force does not exceed centrifugal force iii. critical density less than mean density, centripetal force does not exceed centrifugal force iv. critical density equals mean density, centripetal force equals centrifugal force

322 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 323h. Observe the given statement and its arguments. Which comment is correct? Statement : The density of the universe is assumed by observing the masses that are visible to us within the observable universe.Argument 1 : The density of the universe is calculated by taking the ratio of the total mass of the universe to the total volume of the universe.Argument 2 : We cannot ever truly measure the actual density of the universe because the universe is so vast that we can never know the true mass of the universe and the true volume of the universe.i. Statement and argument 2 are incorrect but argument 1 is correct.ii. The statement is wrong. Arguments 1 and 2 are correct. iii. Statement and argument 2 are correct. Argument 1 is incorrect. iv. Arguments 1 and 2 are incorrect. The statement is correct. i. What is represented by the slope of the straight line shown in this graph?i. Hubble’s law ii. Hubble’s constant iii. Hubble’s observation iv. Hubble’s telescope j. When can we hypothesize a universe that expands forever?i. if gravity becomes zero earlier than expansion force ii. if gravity becomes zero later than the expansion force iii. if gravity and expansion force become zero at the same time iv. if gravity and expansion never become zero a. ii b. iii c. iii d. i e. i f. iii g. iv h. iii i. ii j. iAns of MCQSTEP22. Very short questions a. Study the given concept map and identify the type of universe B.Mean density of A > Critical density > mean density of Bb. The Hubble’s constant measures 73km/s/Mpc. What does this mean? c. Which set of forces was born during the Big Bang?d. What do you mean by Big Bang Theory? e. What are the required conditions for a universe to be open?

324 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 325f. Some galaxies are travelling faster than the light. What does this suggest? g. What is the main factor that determines the fate of the universe? h. If the velocity of galaxies and the gravitation became zero at the same time, what kind of universe would be formed?i. What is the process in which every single matter in the universe will start to condense and change into a single point of zero volume? STEP33. Short questions a. Why is gravitation an important factor in determining the fate of the universe? b. Differentiate between the close universe and the open universe. c. How does Hubble’s law support the theory of the Big Bang? d. The distance between the sun and the earth is relatively constant, even though the universe is expanding. Explain.e. Discuss the similarities between the open universe and the flat universe. f. The balance between gravitation and expansion forces gives birth to a flat universe. Explaing. Why is the Big Bang the most accepted theory of the origin of the universe? h. Under what conditions the universe will collapse into itself as a single primaeval atom ?STEP44. Long questions a. Study the given graph and answer the following questions.i. What should be the relation between critical density and the mean density of the universe to create universe A?ii. What type of universe is B?

324 univeRse Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 325iii. How will universe C die? iv. Which universe will last longer among them?b. What happens to the universe if the mass present in the universe produces gravitation stronger than the expansion forces? Explain. A closed universe was born from the big bang and it will end with the big crunch. Clarify the statement.c. Answer the following questions based on the given figure. i. Which model of the universe is the above picture trying to represent? ii. What are the required conditions for the creation of such a universe? iii. How will such a universe come to an end? iv. What is the relation between the density of this universe with critical density?d. Based on the Big Bang theory, the universe is expanding. What does the observation from Hubble’s telescope suggest? What might be the shape of our universe? Does it expand forever? Put your opinion. e. Study the features of the various models of the universe and answer the following questions. Universe model (A) Universe model (B) Universe model (C)Gravitation produced from its density is exactly sufficient to halt the expansion of the universe the mean density of this universe is lesser than the critical density The gravitation of this universe does not become zero, even when the force of expansion from the Big Bang is already zero What type of universe is model A? How is the Model A universe going to end? What happens to the fate of universe A, if its mean density becomes double than the critical density?♦♦♦

326 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 3271. Information and communication technology: If we use modern technologies and tools for transferring information, then it is called information and communication technologies. 2. Signals : Signals are physical quantities that change with time. 3. Analogue signals : The analogue signals are continuous signals that change continuously with time. 4. Digital signal : A signal that changes in segments and changes by only two fixed values continuously along with the time is called a digital signal.5. Bit : Bit is the smallest unit of computer memory. 6. Byte : A byte is a set of eight bits. 7. Signal transmission: The process of sending and receiving signals from transmitter to receiver is called signal transmission. 8. Analog communication: The process of transferring data with the help of analog signals from the transmitter to the receiver is called analog communication. 9. Digital signal transmission: Digital signal transmission is the process of sending information over physical communication media in the form of a digital signal.10. Baseband transmission: The digital signal transmission in which a digital signal is sent without converting into an analogue signal is called baseband transmission. Key terms and terminologies of the unitSequence of Curriculum Issued by CDC Digital signal and introduction to bit and byte Digital signal transmission Positive and negative impacts of digital technology in daily life Concept of Netizenship, online reputation, and digital wellbeing Preparation and presentation of audio or audio-video material Recording of audio and audio-video from mobile phones or computers  Audio or audio video editing (cutting and joining only)UNITInformation and CommunicationTechnology (ICT)13Estimated teaching periods Theory Practical5 5Mahabir Pun, born on March 17, 1955, in Nepal, is renowned for his pioneering work in wireless technology and rural development. He has revolutionized connectivity in remote Himalayan communities through initiatives like the Nepal Wireless Networking Project, providing internet access and catalysing education and economic growth. Pun's innovative endeavours have earned him global acclaim, driving rural development and narrowing the digital divide in Nepal. Mahabir PunAbout the Nepalese Scientist

326 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 32711. Broadband transmission: The digital signal transmission in which digital signals are converted to analogue, transmitted, received and converted back to digital signals is called broadband transmission. 12. Components of digital communication: The components of digital communication are source, input transducer, encoder, modulator, channel, demodulator, decoder, output transducer and output signal.13. Channel : A channel is a path in which signals transfer from transmitter to receiver. 14. Digital telecommunication: The electronic transfer of data over a long distance using cables, fibre optics, Wi-Fi etc is called digital telecommunication. 15. Digital media : The medium through which electronic devices are used for communication is called digital media. 16. Digital television : The high-definition televisions that use digital signals for communication are digital televisions. 17. Digital library : A digital library is a website which has a collection of textbooks, teacher guidebooks and other e-books18. Online newspaper: The newspapers that are available on the internet are called online newspapers. 19. Digital payment: The act of paying bills through digital banks is called digital payment. 20. Social Networking Sites: Social Networking Sites (SNS) are a huge digital platform where many people can stay connected and share opinions. 21. Digital integrity : Digital integrity is a concept in which we have rights to our digital lives, our privacy and our digital media and no one has the right to alter, use or store our digital data without permission. 22. Digital footprint : A digital footprint is data that is left behind on the internet whenever we use anything on the internet. 23. Citizen of the net: Citizen of the net means everyone who has an equal right to use and actively participate in the internet. 24. Digital citizenship : The state of a person who uses the internet and is skilled in using the internet safely is called digital citizenship. 25. Netizen : A netizen is a person who frequently uses the internet for education, information, business, entertainment or any other reason. 26. Netizenship : Netizenship means every activity that a netizen must do to make a healthy internet environment. 27. Netiquette : Netiquette (Characteristics of a good netizen) means the polite and responsible way of treating people in the online world. 28. Digital well-being : Digital well-being is the practice of maintaining a healthy and balanced relationship between real life and technology. 29. Online Reputation: Online reputation is the public image of a person or business based on the information that appears about them online. 30. Video editing : The act of cutting, modifying and merging videos is called video editing. 31. Video cutting : The act of removing certain parts of the video is called video cutting. 32. Video merging : The process of joining multiple clips is called video merging. 33. Audio editing : The act of cutting, modifying and merging audio is called audio editing.

328 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 329IntroductionInformation is a set of data. The act of telling information to others is called communication. If we use modern digital technologies for transferring information, then it is called information and communication technologies. The devices such as laptops, computers, mobiles, ground stations, satellites, dish TV, radio, Fax machines, telephones, internet etc are called information and communication tools. ICT and ICT tools can be used for communication because of the internet. These ICT tools use signals to transfer data from one place to another. The signals can be either digital or analogue. These signals can be produced, stored and transferred using ICT tools. Lately, digital technologies have skyrocketed. It has revolutionized business, transportation, education, agriculture and communication as well. Digital technologies have given birth to digital television, digital media and digital telecommunication regarding information and communication. The impact of digital technologies in the field of information and communication has hundreds of benefits as well as hundreds of disadvantages. We are a citizen of the net and we have the right to use the internet for our benefit but we should always follow computer ethics and be a very good netizen. We should be aware of digital well-being and online reputation. Being able to access the internet, audio recording applications, video recording applications, audio editors and video editors is a very good skill in the current world. SignalSignals are physical quantities that change with time. It could be codified messages, data and information that are sent from sender to receiver. It could also be electrical signals, radio waves, light waves and so on. The signals are broadly divided into two groups. They are analogue signals and digital signals. Analog signalThe analogue signals are continuous signals that change continuously with time. It is represented by a sine wave. It is used to represent the physical quantities that change continuously. It cannot be represented by 0 and 1. Analogue signals cannot be coded or compressed, so there is more chance of a decrease in the quality of data during transmission. Analogue signals could be sound waves, light waves, infrared radiations, radio waves, electricity, the hand of clocks etc. Analogue signals cannot be stored in storage devices. Analogue-to-digital converter devices change an analogue signal into a digital signal in electronic devices such as microphones. Digital signalA non-continuous electrical signal having discontinuous discrete values with time is called a digital signal. It is represented by square waves. It is used to represent the physical quantities that change in the segments. It can be represented by 0 and 1. Digital signals can be coded and compressed. So, there is less chance Fig: analog signalDigital TV, Dish TV, satellite TV etc uses digital signal.MEMORY TIPS

328 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 329of data loss during transmission. Digital signals are created by mobile, computer, monitor of digital thermometer, audio files, video files, digital photos etc. It can be stored in storage devices. Digital to-analogue converter devices change digital signals into analogue signals in electronic devices such as speakers. Number of digitPossible combination1 0 and 12 00, 01, 10 and 113 000, 001, 010, 011, 100, 101, 110 and 111FACTS WITH REASONSConversion of analog signals to digital signals is preferred. Conversion of analog signal to digital signal is preferred because the digital signal has less chance of error, less external interference and less chance of cross-talk compared to analog signals. Differences between digital signal and analog signalS.N Analog signal S.N Digital signal1. The analogue signals are continuous electrical signals that change continuously with time.1. A non-continuous electrical signal having discontinuous discrete values with time is called a digital signal. 2. It is represented by a sine wave. 2. It is represented by square waves.3. Analogue signals cannot be coded or compressed.3. Digital signals can be coded and compressed.4. It can be converted to digital signal by analogue to digital converter (ADC).4. It can be converted to analogue signal by digital to analogue converter (DAC).Concept of Bit and ByteBit Bit is the smallest unit of computer memory. It is formed from the word binary digit. It can store a maximum of two different values. It could be either 0 or 1. Four bits make 1 nibble. Eight bits make 1 byte.ByteA byte is a set of eight bits. It works as a single unit. 1024 bytes make 1 megabyte. 1024 MB makes one gigabyte. 1024 GB makes one terabyte (TB). Time(seconds)0.51 Amplitude (volts)Fig: digital signal2 nibbles make one byte.MEMORY TIPSUnits of storage capacity of computer memory are bits, bytes, megabytes, gigabytes and terabytes. MEMORY TIPS

330 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 331Signal transmissionThe process of sending and receiving signals from transmitter to receiver is called signal transmission. The transmitter, channel and receiver are three main components of signal transmission. The transmitter produces signals, modulates signals, and gives them to the channel. The channel receives a modulated signal and transfers it to the receiver. The receiver takes the signal from the channel, removes modulation, repairs it and changes it into the desired form. There are two types of signal transmission. They are analog communication and digital communication. Digital communication is further classified as baseband transmission and broadband transmission. Analog signal transmission (Analogue communication)The process of transferring data with the help of analog signals from the transmitter to the receiver is called analog communication. Analog input → Input transducer → modulator → channel → demodulator → output transducer → output signal The features of analog communication are:i. The signal is never converted into digital signal. ii. It can be affected by external interference.iii. Signals cannot be coded in analog communicationiv. It uses low-bandwidthv. Data processing work is not easy.vi. There is a chance of error during data processing. Example of analogue signal transmission:Landline phone uses analogue signals for effective transmission of voice. The microphone of the landline phone receives sound. Sound is an analog signal. Sound is converted to electricity which is also an analog signal. That electric signal is transmitted to the receiver. The speaker changes it into sound and it can be heard. The analogue signal is transmitted from sender to receiver without changing into a digital signal. Therefore, a landline phone call is an example of analogue signal transmission.Two police officers talking in traditional walkie-talkie is also analog signal transmission.Digital signal transmission (digital communication) Digital signal transmission is the process of sending information over physical communication media in the form of a digital signal. It is also known as digital communication. signal sender part of digital communication (transmitter): source → filter → ADC → coding → transmitter and modulator → transmissionsignal receiver part of digital communication (receiver): reception → receiver and demodulation of signal → decoder → [DAC to analog signal] or [digital interface to digital signal] Landline phone uses analogue signals for effective transmission of voice. Antenna TV uses potential differences for analogue signal transmission. Electromagnetic waves also can be used for signal transmission. MEMORY TIPS

330 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 331The features of digital communication are:i. The data is changed into a digital signal at least once during the transmission. ii. It is not affected by external interference.iii. Signals can be coded in digital communication.iv. It uses high bandwidth.v. Data processing work is easier.vi. There is less chance of error during data processing. Example of digital signal transmission.Phone call from mobile devices are example of digital signal transmissions because the mobile devices changes our sound into digital signals.Analog signal transmission was used conventionally for long-distance transmission. But nowadays broadband digital transmission is used for long-distance transmission. Some risks of using analog signals for transmission and the way how digital signal transmission has helped to solve them are: i. Analog signal transmission is comparatively expensive and difficult to design. However, it is cheaper and easier to make circuits for digital signal transmission. ii. Analog signal transmission has more chance of cross-talk and signal overlapping. However, there is very little chance of cross-talk and signal overlapping in digital signal transmission. iii. There is more chance of error in analog signal transmission but codes are used to find and correct errors in digital signal transmission. iv. There are more insecurities in analog signal transmission but encoders are used to compress data and increase security in digital signal transmission. There are two types of digital transmission. They are baseband transmission and broadband transmission. A. Baseband TransmissionBaseband transmission is a type of digital transmission in which a digital signal is sent by the sender and a digital signal is received by the receiver directly. The digital signal is not converted into an analogue signal during transmission. The digital signal transmission in which a digital signal is sent without converting into an analogue signal is called baseband transmission. We can connect two desktop computers or laptops by ethernet cable and transfer data. It is an example of baseband transmission. baseband transmission channels are:Sender ICT tool → digital data → encoder →digital signal → decoder → digital signal → receiver ICT tool The features of baseband transmission are:i. Signal is transferred and received from the same channel.We can connect two desktop computers or laptops by ethernet cable and transfer data. It is an example of baseband transmission.MEMORY TIPSBaseband transmission can transfer video files but cannot make video calls. MEMORY TIPS

332 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 333ii. It sends signals at a lower frequency than broadband. iii. It is mostly used for short-distance communication.iv. Data is sent and received from the same channel. It has only one channel. The advantages of baseband transmission are its cheaper and easier to use. The disadvantage of baseband transmission is that it can send data in a short distance only. B. Broadband TransmissionBroadband transmission is the type of digital transmission in which digital data is sent by the sender and that digital data is converted to analogue signal. Then the receiver receives that analogue signal and converts it back to digital signals. The digital signal transmission in which digital signals are converted to analogue, transmitted, received and converted back to digital signals is called broadband transmission. Sending emails, chatting in Messenger, sending photos in Viber, making audio calls, making video calls, digital telecommunication etc are some examples of broadband transmissions. The broadband transmission channel is:modulating signal modulator modulated signal Carrier signals The features of broadband transmissions are: i. It has two different channels (two separate cables) to send and receive signals ii. It sends signals at a very high frequency than the baseband.iii. It requires modulation. iv. It can be coded. v. It has less chance of cross-talk. The advantage of broadband transmission is it can be used for long-distance transmission. The disadvantage of broadband transmission is its construction is complex and difficult and its installation cost is high. Components of digital communication systemThe components of digital communication are source, input transducer, encoder, modulator, channel, demodulator, decoder, output transducer and output signal.Source: Source produces analog signals for transmission.Input transducer: The input transducer receives analog signals and changes them into electrical signals.Encoder: The encoder compresses data to minimum bits.Broadband transmission needs a modulator and demodulator. MEMORY TIPSBandpass channel is a communication channel whose bandwidth does not start from zero.MEMORY TIPS

332 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 333Modulator: The modulator will modulate the signal, change it into an analog signal and pass it into the channel.Channel: Channel is a path in which signals transfer from transmitter to receiver. Demodulator: It demodulates the received signal. It removes the additional information. Demodulator is the first stage for receiving signal. Decoder: The decoder changes demodulated analog signals into digital signals. It helps to reduce errors in output signals.Output transducers: Output transducers change decoded signals into original physical information. Output signal: Output signals mean the final signal given by the output transducer. It is exact original physical information. Fig: Components of digital communication systemAdvantages of digital transmissionThe advantages of digital transmission are higher security, less external interference, less chance of cross-talk, error detecting and correcting codes can be used and cheaper to design circuits. Effect of digital technology in the development of information and communication technology:Information and communication were harder, slower and expensive. However, it has been easier, faster and cheaper nowadays. The development of digital technologies has influenced information and communication in many ways. For example, it has brought huge changes in digital telecommunication, digital media and digital TV. It has connected the world. The entire world now appears like a global village. Digital telecommunication: The electronic transfer of data over a long distance using cables, fibre optics, Wi-Fi etc is called digital telecommunication. Digital signal transmission is possible due to digital

334 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 335technologies. Nowadays we can use the internet, internet phones and software to make audiovideo calls. Multiple telephone calls can be made from the same channel at once. It has made communication easier. Digital media:Social networking sites, blogs, vlogs, online news, online banking, YouTube, Facebook, online TV, audio-video maker, audio-video editor, cloud computing, live audio-video calls, tweeting etc are various modes and means of communication. All of them are possible due to digital media. The medium through which electronic devices are used for communication is called digital media. These mobile applications, digital content and various software are digital media. Digital television The high-definition televisions that use digital signals for communication are digital televisions. Satellite television, cable television, mobile/portable television, terrestrial signal television etc are some digital televisions. Before these televisions were television antenna television was popular. Nowadays, dish TV is widely available throughout the country. Dish television is a television that receives digital signals from satellites using a dish. Effect of digital technology on human lifeDigital technology has affected many fields in society. It has provided aid in agriculture, banking, education, medicine, mining, space travel, business and entertainment. Every infrastructure of development is now faster, easier and cheaper. There are numerous benefits of digital technologies used in our daily lives. Despite benefits, there are some side effects as well. Artificial intelligence has played major role in digital technology nowadays. AI can now help to make blog, website, codes, picture, videos, counselling, create music, create art, help in communication and help in research.Positive impacts of digital technologies used in our daily life:The positive impacts of digital technology are digital libraries, online newspapers, digital payment, online business, social networking sites, entertainment etc.a. Digital libraries:A digital library is a website which has a collection of textbooks, teacher guidebooks and other e-books. Digital libraries are helpful for students in their studies. It does not waste paper. No need to transport the book. Anyone can download, share and use e-books for free. b. Online newspaper:The newspapers that are available on the internet are called online newspapers. For example, www.gorkhaptra.com. It makes us aware of the current affairs of the world. We can easily receive national and international news. c. Digital payment:The act of paying bills through digital banks is called digital payment. Digital payment is very helpful because we do not need to carry cash for shopping. If we pay revenue, tax etc. from digital payment we do not need to waste time. It can be used for booking

334 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 335hotels, movie tickets, bus tickets etc. d. Business:Many businesses can advertise their brand and their products online on various websites and social networking sites. Online business, online purchases and digital payment have made our lives easier.e. Social networking sites (SNS):Social Networking Sites (SNS) is a huge digital platform where many people can stay connected and share opinions. Some positive impacts of SNS on children are aid in education and entertainment and keep them connected to friends and families. f. Entertainment:Digital technology has revolutionized entertainment in many ways. We can access any entertainment websites by using ICT tools and the internet. Digital media such as YouTube, Netflix and others are sources of entertainment. We can easily access music, movies, art and many others throughout the entertainment. Online games are a source of entertainment. g. Education:Digital technology has helped millions of students to take part in online classes. The government launched many e-classes to support students in their studies. Students could access educational articles online. Students could access the digital library. Any resource of education is available online. h. Banking:Digital technologies have helped banks to go online. We can use mobile banking, e-banking, automated tailoring machines, digital payment, digital banks etc. for paying bills, purchasing goods, receiving salaries, transferring balance, recharging TV and internet, top up mobile etc.i. Information and communication:Digital telecommunication has helped us to connect all over the world. We can watch various news, drama and movies on digital television. Digital media such as Facebook, YouTube etc. helps in communication and entertainment. Facebook Messenger, viber, WhatsApp app etc help in audio calls, video calls, sharing photos, videos etc. j. Health and medicine:Many digital technologies such as digital thermometers, digital sphygmomanometers, MRI machines, online health guidance, articles on health and medicine, online appointments with doctors etc. have significantly improved health facilities. B. Negative aspects of digital technologyNegative impacts of digital technologies on human beings:The negative impacts of digital technology are poor social interaction, a decrease in physical activity, cyberbullying, cybercrimes, obesity, physical discomfort etc. i. Some online newspapers may be fake and they may spread false news. We cannot use it without the internet and ICT tools.

336 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 337ii. Excessive screen time on social networking sites can cause mental illness because a person could be addicted to social networking sites. Cyberbullying, cybercrime, online defamation, hate speech etc. can cause stress, depression and anxiety in people.iii. Some threats of digital payment are sometimes transactions will be unsuccessful and hackers can steal our bank accounts. iv. Decrease in physical activity and lack of exercise can cause obesity, high blood pressure, uric acid and heart attack.v. A person lost in the online world could be socially awkward, and less approachable. So, they could miss many golden opportunities in life.vi. Cybercrime such as botnets, phishing, malware and privacy breaches can hurt one's online reputation, revenue of the company and loss of digital integrity. Netizen and Netizenship [Digital citizenship]The terms citizen of the net, netizens, netizenship and netiquette are deeply interrelated. We are called a citizen of the internet nowadays because we have equal rights regarding participation and use of the internet. Citizen of the net means everyone who has an equal right to use and actively participate in the internet. The state of a person who uses the internet and is skilled in using the internet safely is called digital citizenship. A netizen is a person who frequently uses the internet for education, information, business, entertainment or any other reason. Netizenship means every activity that a netizen must do to make a healthy internet environment. Netizenship includes digital citizenship, computer ethics, characteristics of good citizenship etc. Whereas netiquette means the polite and responsible way of treating people in the online world. It means good characteristics of a netizen. The internet has connected the entire world into a global village. We should be aware of our digital well-being and online reputation. Characteristics of good netizenSome common characteristics of a good netizen are listed below: i. A good netizen does not share private information on social mediaii. They are careful while making comments and posts on social media.iii. They are polite in online as well as offline life. iv. Does not pirate songs, videos and other software. They respect the copyright and digital integrity of the author.vi. They are well aware of digital well-being and online reputation management. FACTS WITH REASONSThe digital footprint is important.Digital footprint is important because it determines our digital reputation. If our digital footprint is suspicious we will lose our online reputation.Digital integrity is a concept in which we have rights to our digital lives, our privacy and our digital media and no one has the right to alter, use or store our digital data without permission. We should use very strong passwords, firewalls, antivirus etc. so that others cannot steal our digital data. A digital footprint is data that is left behind on the internet whenever we use anything on the internet. MEMORY TIPS

336 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 337Digital Wellbeing (Netiquette)Digital well-being is the practice of maintaining a healthy and balanced relationship between real life and technology. It helps us to be socially, mentally, physically and emotionally healthy.We can truly obtain digital well-being when we maintain a proper balance between the amount of time we stay online and offline. We should not use ICT tools and digital media for too long otherwise it has negative impacts on our physical, mental, social and emotional health. We can use digital well-being applications to track our screen time. Excessive screen time on social networking sites can cause mental illness because a person could be addicted to social networking sites. Cyberbullying, cybercrime, online defamation, hate speech etc. can cause stress, depression, loneliness, aggressiveness, social isolation, low self-esteem and anxiety in people. Advantages of digital well-beingThe importance and advantages of digital wellbeing for us are:i. It prevents us from being addicted to technology, the internet and social media.ii. It reduces stress and anxiety.iii. It increases our productivity in education, life and work.iv. It makes us physically, emotionally, mentally and socially healthy. Precautions for Digital Well-being i. Turn off mobile notifications in the workplace and school and keep the mobile in silent mode.ii. Fix a particular amount of screen time for social media. iii. Use the digital well-being application to track screen time. It helps us to plan about digital wellbeing.iv. Fix particular age range for mobile applications and other digital media. v. Turn the screen time notification on. Online reputation (Digital reputation)Online reputation is the way that a person or business is observed based on the information that appears about them online. Some examples of online reputation are:i. good online review of a person, brand, product or companiesii. positive and polite posts on social media Social media is one of the major aspects of online reputation because our online activities, pages or persons we follow, pages we like, online posts, comments and chats show our mentality, wisdom and knowledge. People judge us based on these activities. People trust us more if we use our real names on social media. Factors affecting online reputationi. Post made on social networking sites.ii. Comments made on various posts.iii. Review of the product of the company.iv. Respond to the comments of customers or friends The page followed, comments made, posts shared etc. allow others to judge our intelligence. MEMORY TIPS

338 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 339Importance of online reputation for a personi. more people will trust usii. people will have a positive attitude toward us iii. good online reputation will not give us stress Importance of online reputation for companyi. Increase in goodwill.ii. growth in business and more revenue iii. More trust from customers FACTS WITH REASONSWe must manage our online reputation. We must manage our online reputation because based on online reputation people will judge us. They will treat us according to our online reputation. Online Reputation Management (ORM)The process of managing online image of a person, company or a brand is called Online Reputation Management (ORM). Some guidelines while surfing the internet to maintain an online reputation are:i. People as well as companies should use internet security measures. Use strong passwords. Do not share passwords. Update devices. Use antivirus, firewall, Windows Defender etc. ii. Persons and companies should have accounts on every available popular social networking site.iii. Person and companies should respond positively in comments on their post.iv. We should be very careful about what to post or comment on social networking sites. We should be polite and very careful while making comments, posting texts etc.v. Delete the fake account and use the real one. We have to use actual information while making accounts. We should not make fake accounts. Use the same profile name for any social account.vi. Apologise for his hurtful comments and never repeat them. Importance of digital reputation management. The importance of digital reputation management is:i. It helps to increase trust between us and our friends, families, followers and customers.ii. It reduces bad reviews about us, our products, our brands and our business and helps to increase good reviews.iii. For a good online reputation, we focus on internet security. It helps to protect our digital data and our accounts and prevents hacking.iv. Failure to manage digital reputation will harm our prestige and companies could lose customers and revenue. FACTS WITH REASONSPeople must manage their online reputation.People must manage their online reputation because the online reputation also affects their real life. If internet security is weak, privacy setting is weak other people can steal our password and use our accounts for cyber crime, bullying and to do other socially unacceptable activities. It can hurt our online reputation. MEMORY TIPS

338 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 339ACTIVITY 1Observe the digital technologies used in your school. List out their purposes, merits and demerits. Audio-visual MaterialsAudio-visual materials are very important. It can work as memory, proof and storage of events. Audio-visual recording is an important skill because it helps to record important events of life, create educational videos, make entertainment videos, record research and do project work. Mobile devices, microphones and computers can record audio. Mobile phones, digital cameras and laptops can record videos. We can download video editing applications from Windows Store, App Store and Play Store. A video file extension is always mentioned with the video file. Some common video file formats are .3GP, . SVI, .MOV, MP4 etc. Some popular audio file formats are .MP3, .WAV, .WMA etc. Video editing The act of cutting, modifying and merging videos is called video editing. Some applications that can edit videos are Free Video Cutter, Media Cope, Video Edit Master, Adobe Premiere Pro, Filmora etc. Making a video file The general procedure for making the audio-visual material of length 5 minutes is discussed in short below:i. Record video: We can use a digital camera to record videos on any topic let’s say: ‘monocotyledons’ii. Cut videos: We can cut certain parts of videos from video-cutting applications on computers or mobiles. Tap the pencil icon in the bottom corner of the screen at the beginning and at the end of the video to be cut. Then click save. iii. Merge videos: Open the application. Select multiple videos to be merged. Then click done. When the video is merged, we can click save. iv. Record audio: We can use mobile devices, laptops or iPhones to record audio. First, we have to launch a voice recorder. Then start the recording. We can pause or stop the recording as required. v. Dubbing: The original sound of the video may not be good. So, we should remove that sound. Then we have to merge that video and recorded audio. It helps to produce a good-quality video. Video cuttingThe act of removing certain parts of the video is called video cutting. The objective of video cutting is to remove undesired video. If we need to make the video shorter let’s say a 3-minute length then we can use a video editor.We might need to cut some parts and then merge the remaining parts again. So first let’s cut certain parts of the video and merge them back.

340 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 341Video cutting is done in the following ways.i. Launch video editing application.ii. Start a new project and select or upload the desired video in the library of the video cutter.iii. Select the video from the library.iv. Play the video. Mark start time and end time. Press trim. v. Check the length of the video. Select a newly made clip. Press “finish” the video and press export. vi. Select the location to save the file and press save. Video mergingThe process of joining multiple clips is called video merging. The objective of merging videos is to join many small clips to make final videos. The video merging is done in the following ways:i. Launch video editor. Add video clips in the library of the editor.ii. Put required videos in the editing panel. Select videos that should be merged.iii. Then click on start merge or finish video. iv. Select the location to save the file and press save. Audio editing The act of cutting, modifying and merging audio is called audio editing. Some applications that can edit videos are mp3 cutter, www.audacityteam.org online audio editor etc. Making an audio file The procedure to make an audio file is discussed below:i. Record audio: We can use mobile devices, laptops or iPhones to record audio. First, we have to launch a voice recorder. Then start the recording. We can pause or stop the recording as required. ii. Cut audio: We can download the Audacity application or any audio editing application from the Play Store or websites. And use it to edit audio. We can cut the required audio on this application.iii. Merge audio: We can merge multiple required audios on an audio editing application.Then we can save the work. Finally, an audio file is formed. Cutting an audio file and merging two audio files can be done in MP3 cutters similar to video cutting and video merging. ACTIVITY 2Make a ten-minute audio-visual material on the topic of climate change. ACTIVITY 3Take audio-visual material from activity 2 and summarize it into a 3-minute audio-visual material.

340 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 341HOT SKILL HIGHER ORDER THINKING SKILL1. Digital technologies played significant roles in continuing society during the coronavirus pandemic. Digital technologies played significant roles in continuing society during the coronavirus pandemic in the following ways:i. Social networking sites kept families connected so that they did not need to go outside.ii. Social media sites such as YouTube, Netflix etc. provide entertainment for people.iii. Digital banks such as Esewa, Khalti, etc. helped in online payments of electric bills, TV bills, online purchases etc.iv. Online businesses, online shops etc. helped people in buying and selling. 2. Sneha has significantly decreased screen time, does not use digital gadgets, does regular exercise, meditates, behaves well with others and contributes to social work. What is he trying to achieve? What benefits will it bring to her? Sneha is trying to achieve digital well-being by significantly decreasing screen time, decreasing the use of digital gadgets, exercising regularly, meditating, behaving well with others and contributing to social work.Its benefit for her is, that she will be socially, mentally, physically and emotionally healthy. 3. The entire world is now a global village due to digital technology. Explain. Digital technology such as ICT tools and the internet has connected people worldwide. Communication, sharing information, business, education etc. is now possible beyond political or geographical boundaries. With faster communication and easier online buying and selling, online education has made the entire world a global village. 4. Krishna has a fake account on Facebook. He uses it to follow others and make hurtful comments. But the friends now knew it was him. a. What wrong did he do as a netizen? What should he have done instead? As a netizen, his crime is the ‘use of fake information to make an account’ and cyberbullying. He should have used real information to make social accounts. He should have not used hateful comments. He should have made positive and encouraging comments. b. What can he do to improve his online reputation now? He can do the following things to improve his online reputation now:i. Delete the fake account and use the real one.ii. Apologise for his hurtful comments and never repeat them. 5. Why should we not use the digital content of other people? We should not use the digital content of other people because it is a cybercrime. It reduces their income. Using digital content without permission makes us bad netizens.6. Balance between physical well-being, mental well-being, emotional well-being and social well-being is very important for digital well-being. Explain. Digital well-being is an act of maintaining a balance between online and offline life for overall health and happiness. To obtain a digital well-being balance between physical well-being, mental well-being and social well-being is very important. Which is explained below:i. Spending a very long time on digital devices can cause eye strain, headache, back pain etc. So,

342 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 343we must be physically fit and healthy by doing exercise.ii. Excessive screen time can cause stress, anxiety and addiction and make us sick. So, we should limit screen time. Sleep enough and stay mentally fresh and healthy. iii. If we cannot stay emotionally healthy we might make hurtful comments, bully others, get angry and make toxic interactions online. So, we should learn to control emotions and make positive interactions only.iv. A person addicted to the internet may be poor in real-life social interaction. So, we should manage time for social interaction and family gatherings. We should be polite in real life as well as in online social interactions. 7. Children should not use mobile devices, laptops etc. more than 2 to 3 hours per day. Why?Children should not use mobile devices, laptops etc. more than 2 to 3 hours per day because excessive screen time has negative impacts on them. Such as:i. It can increase distress and anxiety in children.ii. It can cause mood disorders in children.iii. Children will involve less in social activities. iv. It will increase depression and hatred in children. 4 STEPS EXERCISE EXERCISESTEP11. Multiple Choice Questions a. What does not represent 1 bit?i. 0 ii. 1iii. 0 and 1 iv. 0 or 1b. What signal transmission technique does not convert digital signal to analogue signal?i. baseband transmission ii. broadband transmission iii. landline transmission iv. optical fibre transmission c. Which of the ways can decline Online Reputation?i. apology ii. respond iii. security breach iv. communicationd. Which of the following is a baseband transmission? Analog signal in channel Digital signals in channel Digital signals sent A BAnalog signals sent C D i. A ii. Biii. C iv. D e. What is the correct order of baseband transmission channel? i. sender ICT tool (transmitter) → digital data → encoder → digital signal →decoder → digital signal → receiver ICT tool ii. analog input → Input transducer → modulator → channel → demodulator

342 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 343→ output transducer → output signal iii. source → filter → ADC → coding → transmitter and modulator →transmissioniv. reception → receiver and demodulation of signal → decoder → [DAC to analogue signal] or [digital interface to digital signal] f. Which of the following is a broadband transmission? i. transmitter: analog signal in channel: analog signal receiver : analog signalii. transmitter: digital signal in channel: digital signal receiver : digital signaliii. transmitter: digital signal in channel: analog signal receiver: digital signaliv. transmitter: analog signal in channel: analog signal receiver : digital signalg. What type of signal is A?A Bsecured by encoding and compression cannot be secured by encoding and compression signali. analog signal ii. digital signal iii. analogue as well as digital iv. emergency signal h. Why should we use internet security and strong passwords in every account? i. otherwise, we can forget passwords and cannot use our accounts ii. weak passwords are not attractive iii. otherwise, hackers can use our accounts for fraud which destroys our online reputation iv. we do not need to use strong passwords i. Abhisekh learnt that he can transfer photos from a laptop to a mobile from Bluetooth as well as a data cable. He also noticed that to transfer data from Bluetooth, a digital photo is sent from a laptop, it is changed in analogue signals and then it is received by mobile and changed into digital photos again. Whereas when the digital photo was sent using a datacable, the digital photo was sent by laptop, digital data was transferred from cable and the digital photo was received by the mobile. Based on this observation choose the best statement. i. data transfer using Bluetooth is analog communication whereas data transfer using datacable is digital communication.ii. data transfer via Bluetooth is digital communication whereas data transfer using a datacable is analogue communication. iii. data transfer through Bluetooth is baseband whereas data transfer through data cable is called broadband is broadband transmission.iv. data transfer through Bluetooth is broadband transmission whereas data transfer through data cable is baseband transmission.j. Mr. Khadka shares conspiracy theories and superstitious beliefs on social media frequently. Which of the following statements is true for his action?

344 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 345i. He has a good online reputation. ii. He is cautious about digital well-being.iii. He is a reputable netizen.iv. He is not cautious about digital well-being and online reputation. a. iii b. i c. iii d. ii e. i f. iii g. ii h. iii i. iv j. iv Ans of MCQSTEP22. Very short questions a. What does data from 0000000 to 11111111 represent?b. Which one is broadband transmission?No. of channel Distance covered Modulator A 1 Short Not needed B 2 Long Needed c. What signal is represented by this wave? d. Give two examples of audio file format. e. Why are we called a citizen of the internet nowadays? f. Make a slogan to raise public awareness on digital well-being. g. When can we truly obtain digital well-being? h. Write the full form of ADC and DAC. i. In which type of transmission, the digital signals are converted into analog signals before passing into the channel?STEP33. Short questions a. Digitization has reduced the burden of carrying cash during buying and selling goods but it is not without risk. Explain. b. If three numbers of binary digits are used to make digital data, what are the possible combinations? Enlist.c. Balance between physical well-being, mental well-being, emotional well-being and social well-being is very important for digital well-being. Explain.d. Mr Y has a fake account on Facebook. He uses it to follow others and make hurtful comments. But the friends now knew it was him.i. What wrong did he do as a netizen? What should he have done instead? ii. What can he do to improve his online reputation now?

344 inFoRMation and coMMunication tecHnoLogy (ict) Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 345e. How has the development of digital technology increased social crimes? Explain briefly.f. Your friend regularly uses the internet for various purposes. He randomly keeps opening websites without taking care of the cautions that pop out. Suggest to him a few internet etiquette that he must follow while surfing on the internet.g. What is copyright? Why should we not use the intellectual property of other people?h. Hari has significantly decreased screen time, does not use digital gadgets, does regular exercise, meditates, behaves well with others and contributes to social work. What is he trying to achieve? STEP44. Long questions a. Study the given conversation and answer the following questions. Umanath: I never give mobile to my child because it ruins their learning ability.Kailash: I disagree! I give my mobile to my child all the time. It helps them to do Homework. Gokul: I believe we should allow children to use mobiles but only for a couple of hours per day.i. Who is well aware of digital well-being?ii. What are the factors necessary for true digital well-being?iii. What are the precautions for digital well-being?b. How can we hear sounds from loudspeakers when someone is singing on a mic? Describe the signal transmission. c. What do you mean by online reputation? What role does it play in the promotion of business companies? What can organizations do to maintain a good online reputation? d. What are social networking sites? How does it affect a child? Mention its two positive effects and two negative effects on them.e. [Sanjila is trying to produce the signals. She is using an electrical transistor to produce ………. signals. She turned the switch on and off alternately. The voltagetime graph of AC will start from zero and shoot directly up to the maximum, stay constant for some duration and drop back to minimum zero. It forms a square wave during the process. The signal produced in this experiment is ……. signal. ………. signal shows the value of the range ………]What kind of signal is formed in this experiment? Mention its range. Enlist the possible combinations of two numbers of this signal formed in this experiment are combined to form data. Draw the voltage-time graph to represent this activity. ♦♦♦

346 ClassifiCation of ElEmEnts Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 347Key terms and terminologies of the unit1. Classification of elements : The process of keeping elements with similar characteristics in the same group and elements with dissimilar elements in a different group is called the classification of elements. 2. Periodic Table : The table, or chart, which is obtained after arranging elements on the basis of similarities and dissimilarities is called the periodic table. 3. Mendeleev's periodic law : Mendeleev's periodic law states that \"The physical and chemical properties of elements are a periodic function of their atomic weights.\"4. Mendeleev's periodic table:The table which is obtained after arranging elements on the basis of increasing atomic weight is called Mendeleev's periodic table.\" 5. Modern periodic law : Modern periodic law states that, \"Physical and chemical properties of the elements are a periodic function of their atomic numbers.\" 6. Modern periodic table : The table which is obtained after arranging elements on the basis of increasing atomic numbers is called the Modern periodic table.\" 7. Isotopes : Isotopes are elements having the same atomic number but different atomic weights. 8. Lanthanides : The 15 inner-transition, radioactive elements from cerium (58Ce) to lutetium (71Lu) along with lanthanum (57La) are called Lanthanides. 9. Actinides : The 15 inner-transition, radioactive elements from thorium (90Th) to lawrencium (103Lr) along with actinium (89Ac) are called Actinides. 10. Periods : In the modern periodic table, there are seven horizontal rows, which are called periods. In a period, elements having gradual change in properties are placed one after another. Sequence of Curriculum Issued by CDC Modern periodic law Introduction to modern periodic table  Structure of modern periodic table, group and period  Sub-electronic configuration of the first 20 elements  s, p, d and f block elements of periodic elements  Position of metals, nonmetals and metalloids in the modern periodic table Periodic variation (variation of atomic size, electro positivity, electro negativity, valency and reactivity)UNITClassification of Elements14Estimated teaching periods Theory Practical7 2Nilam Shrestha Pradhan, born in 1964 in Kathmandu, holds the distinction of being the first female physics professor in Nepal. With expertise in solid-state physics and atomic and molecular physics, she boasts over 30 years of teaching experience and holds a PhD from Tribhuvan University. Pradhan's supervision of numerous research projects has shaped Nepal's future physicists. Nilam Shrestha PradhanAbout the Nepalese Scientist