Modern Concept Science and Technology Book 5 201 b. Among the sound of a girl, boy and adult person, whose sound has the highest pitch? c. Write the name of a source of sound in a laboratory. d. Which organ helps us to detect sound? e. What is the velocity of sound in water? 6. Write any two differences between: a. Light and sound b. Music and noise c. Transverse wave and longitudinal wave d. Pitch and loudness 7. Give reasons. a. Different men have different voices. b. Sound cannot be heard in space. c. Music is tolerable. d. We can hear sound on the earth. e. We have to use electronic device to listen sound on the moon. f. Sound of a girl is sharper than that of an adult man. g. Sound of a big bell in a temple is louder and can be heard over a long distance. 6. Write down the name of following figures and mention one use of each. a. b. c. d. e. f.
202 Modern Concept Science and Technology Book 5 STEP3 7. Answer the following questions a. Define sound energy. b. What is wave motion? Which type of wave is sound? c. Define musical sound and noise. d. What is the speed of sound in air? e. What do you mean by source of sound? Give two examples. f. What is pitch? g. Define loudness of sound. h. Write two characteristics each of the transverse wave and longitudinal wave. i. What do you mean by propagation of sound? j. Can a musical sound for a person be noise for other. Explain your opinion. 8. Observe the diagram and answer the following question. A B a. Which bell produces louder sound and why? b. Which bell produces a sharp sound and why? c. Which bell’s sound can be heard over a long distant?
Modern Concept Science and Technology Book 5 203 Key terms and terminologies of the unit 1. Sources of electricity: The devices which produce electricity are called sources of electricity. 2. Cells: The cells are the sources of electricity which convert a form of energy like chemical energy into electrical energy. 3. Simple cell: A simple cell is a source of electricity which consists of copper and zinc plates dipped into the dilute solution of sulphuric acid. 4. Dry cell: The source of electricity which contains a paste of ammonium chloride instead of liquid acid is called dry cell. 5. Dynamo: Dynamo is a device which converts mechanical energy into electrical energy. 6. Generator: Generator is a device which converts large amount of mechanical energy into electrical energy. 7. Solar cell: Solar cell is a device which converts solar energy into electrical energy. 8. Solar panel: The combination of large number of solar cells to convert solar energy into electrical energy is called a solar panel. 9. Electric circuit: The conducting path made by connecting a cell, a bulb and a switch is called an electric circuit. 10. Electric Loads: The electric devices which convert electric energy into other forms of energy like heat, light, sound, etc. are called electric loads. 11. Switch: Switch is a device which is used to open or close the electric circuit. 12. Conducting wire: These are the medium which carry current from sources to the electric devices. Sequence of Curriculum Issued by CDC Introduction and construction of electric circuit Functions of wire, cell, bulb and switch in electric circuit Safety precautions while using electricity UNIT Electricity 7.3 Estimated teaching periods Theory Practical 6 3 Michael Faraday was an English physicist and chemist. He was born in 1791 and died in 1867 in England. He conducted many experiments contributed greatly to the understanding of electromagnetism. He was the inventor of electrical generator. His electrical generator converted magnetic energy into electrical energy. The generator that is used in producing electrical energy in hydropower plants are developed on the foundation of Faradays invention. Michael Faraday About the Scientist
204 Modern Concept Science and Technology Book 5 13. Open circuit: The circuit in which the switch is off and no current is flowing is called an open circuit. 14. Close circuit: The circuit in which the switch is on and current is flowing through the circuit is called a close circuit. 15. Conductor: Those materials which allow electricity to pass through them are called conductors. 16. Insulators: Those materials which do not allow electricity to pass through them are called insulators. 17. Semiconductors: Those materials which allow partial flow of electricity through them are called semiconductor. Introduction to Electricity Electricity is the most common and useful form of energy. It can be converted into other forms of energy easily. The various kinds of electric devices are used to convert electric energy into other forms of energy. For example, electric lamp, fluorescent lamp, CFL, LED, etc. convert electric energy into light energy. Similarly, electric heater converts electric energy into heat energy; electric motor converts electric energy into mechanical energy; radio, speaker, mobile, etc. convert electric energy into sound energy, etc. Electricity is produced due to the flow of electrons or charges from one place to another. It can flow only through conductors. In this unit we will discuss about different sources of electricity, electric current, conductors, semi-conductors and insulators. Sources of Electricity As we know that electricity is the most common and useful source of electricity to run our modern lifestyle. We use various electric devices in our daily life. For example computer, calculator, radio, television, electric fan, electric bulb, heater, etc. To operate these devices we need electricity. To get electricity we use various devices like simple cell, dry cell, photo cell, dynamo, generator, etc. These devices are called sources of electricity. Thus, the devices which produce electricity are called sources of electricity. The major sources of electricity are briefly described below: The full form of CFL is Compact Fluorescent Lamp and LED is Light Emitting Diode MEMORY TIPS
Modern Concept Science and Technology Book 5 205 a. Cells Cells are the sources of electricity which convert a form of energy like chemical energy into electrical energy. They are the most common sources for direct current. They are used to produce a small scale of electricity. Some cells are also used to store electricity produced by other sources of electricity. There are two types of cells. They are primary cells and secondary cells. Primary cells are also of two types. They are simple cell and dry cell. i. Simple cell As the name suggests, the simple cell is very simple in construction. It contains two metal plates. They are copper plate and zinc plate. These metal plates are dipped into dilute sulphuric acid. Thus, a simple cell is a source of electricity which consists a copper and zinc plates dipped into dilute sulphuric acid. When these metal plates are connected by a copper wire to a bulb, electric charge flows through the wire and the bulb glows. It can produce very small amount of current. Bulb Zinc (cathode) Voltameter Sulphuric acid (H2 SO4 ) Copper (anode) Simple cell FACTS WITH REASONS Dry cell is better than a simple cell, why? Dry cell is better than a simple cell because a dry cell can be easily transported, produce more current and easy to use than a simple cell. Simple cell contains sulphuric acid. Hence, it is dangerous to transport. So simple cell is very rarely used. MEMORY TIPS
206 Modern Concept Science and Technology Book 5 ii. Dry cell A dry cell is a small and portable source of electricity. It contains a paste of ammonium chloride instead of dilute sulphuric acid. The source of electricity which contains a paste of ammonium chloride instead of liquid acid is called a dry cell. At the centre of a dry cell there is a carbon rod covered by a muslin bag. The muslin bag contains a mixture of manganese dioxide and carbon powder. The carbon rod contains a brass cap at its top. The carbon rod, muslin bag and dry chemicals are kept inside the leak-proof zinc container. Dry cells are most commonly used in watch, calculator, torch light, radio, cassette player, etc. b. Dynamo and generator Some of you might have seen a bicycle dynamo fixed on a bicycle. It produces electricity when the wheel of bicycle rotates and lights the bulb. Thus, dynamo is a device which converts mechanical energy into electrical energy. Dynamo produces a small amount of electricity. Similarly, generator is a big dynamo. It produces large amount of electricity. So, generator is a device which converts large amount of mechanical energy into electrical energy. It is used to produce large amount of electricity at homes, schools, industries and power plants. c. Solar cell or photo cell You might have seen solar panels at the rooftops. These solar panels contain cells in them called photo cells. These photo cells convert solar energy into electrical energy. Thus, solar cell is a device which converts solar energy into electrical energy. Single solar cell converts very less amount of solar energy into electrical energy. Zinc container Graphite rod MnO2 Ammonium jelly Dry cell A dry cell contains a paste of ammonium chloride instead of dilute sulphuric acid. So, it is called a dry cell. MEMORY TIPS Bicycle dynamo Solar cell
Modern Concept Science and Technology Book 5 207 So, a large number of solar cells are used together to produce a significant amount of current. Thus, the combination of a large number of solar cells to convert solar energy into electrical energy is called solar panel. In our country, solar panels are mostly used in rural areas for the lighting purpose. FACTS WITH REASONS Use of solar panel should be encouraged, why? Use of solar panel should be encouraged because solar power is a renewable source of energy and it does not produce smoke like other fuels. ACTIVITY 1 Objective : To produce electricity from the potatoes. Requirement : Five big potatoes, five small zinc plates, five small copper plates, copper wires, galvanometer, etc. Methods : 1. Take five big potatoes and place them in a salt solution for about half an hour. 2. Take them out and insert one zinc plate and one copper plate in each of them. Remember that they should not touch each other. 3. Join the plates and galvanometer as shown in the figure and observe the deflection in the galvanometer. 4. Galvanometer shows the deflection which indicates that current is produced in the circuit. 5. Try the same experiment with lemon, orange, apple, etc. Zinc plate Copper plate Potato Copper wire Galvanometer Precaution while Using Electricity Electricity transfers electric energy in the form of moving current. These currents can cause severe accidents when we come in direct contact of it. It can results fire and explosions that causes damage to human and property. Burns, heart attack, injury or falling, nerve damages etc. are some effects of electric current on human. So, we must take precautions while using electricity. Some of the major safety measures to avoid electric shock are: i. Unplug appliances when not in use. ii. Never run current carrying cords under carpets, rugs, doors or windows.
208 Modern Concept Science and Technology Book 5 iii. Immediately replace the damage power socket or cords. iv. Keep electrical appliances and tools away from water. v. Do not put any objects in the plug. vi. Never plug in and out with wet hands. vii. Discourage the long-term use of extension cords. Electric Circuit The conducting path made by connecting a cell, a bulb and a switch is called an electric circuit. Electricity flows smoothly through an electric circuit. In an electric circuit current flows from source to the electric device. The very common example of electric circuit is found in our house wiring. In the house wiring, wires, switches, bulbs and other electric devices are connected to the main supply. It makes a continuous electric circuit. Components of an electric circuit An electric circuit has the following main components: a. Source Electricity is obtained from the various sources like dry cell, dynamo, generator, solar panel, etc. b. Conducting wire These are the medium which carry current from sources to the electric devices. They are made from the conducting wire like copper, aluminium, etc. c. Electric load The electric devices which convert electric energy into other forms of energy like heat, light, sound, etc. are called electric loads. For example, electric bulb, motor, rice cooker, computer, etc. d. Switch It is a device which is used to open or close an electric circuit. Copper wire Switch Dry cell Bulb glowing Electric circuit
Modern Concept Science and Technology Book 5 209 Open circuit and closed circuit The circuit in which switch is off and no current is flowing is called an open circuit. In open circuit current cannot flow. So, the devices which are connected in an open circuit do not work. The circuit in which switch is on and current is flowing through the circuit is called a close circuit. In the closed circuit current can flow smoothly. So, the devices connected in a closed circuit can work properly. Copper wire Switch on Dry cell Bulb Copper wire Switch off Dry cell Bulb glowing Open circuit Closed circuit FACTS WITH REASONS Bulb does not glow in an open circuit, why? Bulb does not glow in an open circuit because current does not flow in an open circuit. Differences between open circuit and closed circuit S.N. Open circuit S.N. Closed circuit 1 The circuit in which switch is off and no current is flowing is called an open circuit. 1 The circuit in which switch is on and current is flowing through the circuit is called a close circuit. 2 In an open circuit, current cannot flow. 2 In a closed circuit, current can flow smoothly. Conductor, Insulator and Semiconductors There are different types of materials in our surrounding. They respond electricity in different ways. Some materials allow current to pass easily and some do not. So, depending upon the nature of the materials, they are divided into three categories. They are:
210 Modern Concept Science and Technology Book 5 a. Conductors Those materials which allow electricity to pass through them are called conductors. Iron, copper, silver, gold, etc. are some examples of conductors. Most of the metals are good conductor of electricity. In case of non-metal graphite is used as a conductor. b. Insulators Those materials which do not allow electricity to pass through them are called insulators. Plastic, wood, mud, etc. are some examples of insulators. FACTS WITH REASONS Why is plastic used to cover the wires? Plastic is used to cover the wires because plastic is an insulator which prevents electric shock. c. Semiconductors Those materials which allow partial flow of electricity through them are called semiconductor. Most of the semiconductors are used to make electronic devices like computer, calculator, television, etc. Differences between conductors and semi-conductors S.N. Conductors S.N. Semi-conductors 1 Those materials which allow electricity to pass through them are called conductors. 1 Those materials which allow partial flow of electricity through them are called semiconductor. 2 Conductors work properly at average temperature. Example: aluminium 2 Semi-conductor work properly at high temperature. Example: silicon Silver is the best conductor and lead is the poorest conductor of electricity. MEMORY TIPS
Modern Concept Science and Technology Book 5 211 HOT SKILL HIGHER ORDER THINKING SKILL 1. What is source of electricity? List out few sources of electricity. The devices which produce electricity are called sources of electricity. Sources of electricity are: cell, dynamo, solar panel etc. 2. Define cell. List out its types. The cells are the sources of electricity which convert a form of energy like chemical energy into electrical energy. Types of cells are: i. Simple cell ii. Dry cell iii. Solar cell / photo cell 3. Write any two differences between simple cell and dry cell. Differences between simple cell and dry cell are: S.N. Simple cell S.N. Dry cell 1 A simple cell is a source of electricity which consists a copper and zinc plates dipped into the dilute solution of sulphuric acid. 1 The source of electricity which contains a paste of ammonium chloride instead of liquid acid is called a dry cell. 2 Simple cell produces less voltage. 2 Dry cell produces more voltage. 4. Write a difference between dynamo and generator. A dynamo produces little amount of current but a generator produces large amount of current. 5. Draw a clear diagram of a simple cell and label it. Bulb Zinc (cathode) Voltameter Sulphuric acid (H2 SO4 ) Copper (anode)
212 Modern Concept Science and Technology Book 5 6. What is an electric circuit? Draw a diagram of closed circuit. The conducting path made by connecting a cell, a bulb and a switch is called an electric circuit. Copper wire Switch on Dry cell Bulb 7. What is an insulator? Give two examples. Those materials which do not allow electricity to pass through them are called insulators. Examples: mud, air 8. Identify the given substance as insulator, semiconductor or conductor. Graphite, plastic, silicon, germanium, copper, dry wood S.N. Object Nature 1 Graphite Conductor 2 Plastic Insulator 3 Silicon Semi-conductor 4 Germanium Semiconductor 5 Copper Conductor 6 Dry wood Insulator 33 STEPS STEPS EXERCISE EXERCISE STEP1 1. Fill in the blanks with appropriate words. a. Electricity is a form of ___________________ . b. Charges are of _____________ types.
Modern Concept Science and Technology Book 5 213 c. In an open circuit bulb ___________________ . d. Combination of many cells is called___________________ . e. Dynamo is a ___________________ of electricity. 2. Write True for the correct and False for the incorrect statements. a. Electricity is a form of energy. b. Concentrated sulphuric acid is used in simple cell. c. Dynamo is a source of electricity. d. Current flows in open circuit. e. Pure water is a good conductor of electricity. 3. Select the best answer from the given alternatives. a. Opposite charges: i. attract each other ii. repel each other iii. do not do anything iv. none of the above b. Which one of these is a conductor of electricity? i. paper ii. wood iii. brick iv. copper c. Which one of these is an insulator of electricity? i. iron ii. air iii. gold iv. silver d. Which of following is not a source of electricity? i. heater ii. dry cell iii. solar cell iv. dynamo e. In which of the following circuit does load work properly? i. closed circuit ii. open circuit iii. short circuit iv. all of above
214 Modern Concept Science and Technology Book 5 4. Match the following. a. Conductor i. Bulb glows b. Insulator ii. Bulb doesn’t glow c. Semiconductor iii. Iron d. Open circuit iv. Silicon e. Close circuit v. Pure water STEP2 5. Answer the following questions in one word. a. Which device is used on bicycle for lighting purpose? b. In which type of cell there is use of a liquid chemical substance? c. What is the name of a device which is used to make an electric circuit close and open. d. Give one example of a semiconductor. e. Which kind of substance supplies the current properly at high temperature? 6. Write any two differences between: a. Simple cell and dry cell b. Conductor and insulator c. Electric cell and bulb d. Conductor and semi-conductor e. Open circuit and close circuit f. Generator and dynamo 7. Give reasons. a. Dry cell is better than a simple cell. b. Light does not glow in an open circuit. c. Plastic is used to cover electric wires. d. Simple cell is dangerous to transport. e. Use of solar panel should be encouraged.
Modern Concept Science and Technology Book 5 215 8. Write down the name of following instruments and mention one use of each. a. b. c. Bulb Zinc (cathode) Voltameter Sulphuric acid (H2 SO4 ) Copper (anode) d. e. STEP3 9. Answer the following questions. a. What is electricity? b. What is a dry cell? c. Define a simple cell. d. What do you mean by sources of electricity? Give any two examples. e. Define electric load and conducting wires. f. What are open and close circuit? g. Write the full form of CFL and LED. h. Write the definition of conductor, insulator and semiconductor with one example of each. i. Write the advantages of a dry cell over simple cell. j. What is a solar panel? 10. Draw the diagram of the followings: a. Draw a well labelled diagram of a simple cell. b. Draw a well labelled diagram of a dry cell showing its interior parts.
216 Modern Concept Science and Technology Book 5 Unit 8 The Earth and Space Fig: Solar system Fig: Phases of Moon
Modern Concept Science and Technology Book 5 217 Key terms and terminologies of the unit 1. Solar system : A group of eight planets and their satellites, comets, asteroids, etc. which surround the sun is called solar system. 2. Planets : Those heavenly bodies which revolve around the sun in their own elliptical orbit are called planets. 3. Stars : The bright twinkling heavenly bodies which produce their own light continuously are called stars. 4. Satellites : Satellites are the heavenly bodies or objects which revolve round the planet in their own orbit. 5. Moon : The moon is the only natural satellite of the earth. 6. Dwarf planets : The round heavenly bodies which are not the moons of other planets and orbit the sun are called dwarf planets. 7. Asteroids : The heavenly bodies which are found in between the orbits of Mars and Jupiter are called asteroids. 8. Meteoroids : The lump of rocks and metals which are smaller than asteroids and found in the solar system are called meteoroids. 9. Meteors : Meteoroids that burnt in the atmosphere of a planet are called meteors. 10. Meteorites : If the meteoroids do not burn completely in the atmosphere of the planet and reach to the surface of the planet, they are called meteorites. Sequence of Curriculum Issued by CDC Introduction to sun, earth, moon and other heavenly bodies UNIT The Heavenly Bodies 8.1 Estimated teaching periods Theory Practical 8 2 Nicolaus Copernicus was a Polish astronomer. He was born in 1473 and died in 1543 in Poland. He proposed that the planets have the sun as the fixed point to which their motion are referred. He also proposed that earth revolves round the sun and rotates once daily on its own axis. Due to this contribution in astronomy, he is known as the father of the solar system. Nicolaus Copernicus About the Scientist
218 Modern Concept Science and Technology Book 5 The sun The sun is a massive ball of fire. It is a medium sizedstar closest to the earth. It is very hot because it has hot gases in it. The sun radiates large amount of heat and light continuously. The sun looks small because it is about 150 million km far from the earth. It takes about 8 minutes and 20 seconds to reach the light from the sun to the earth. The sun is the only natural source of heat and light for the earth. It provides warmth and maintains temperature in the earth. It causes water cycle in the earth. Plants use sunlight to prepare food through the process of photosynthesis. The food is then eaten directly or indirectly by the living organisms. Heat of the sun causes the air to blow. Therefore, there will be no life in the earth without the sun. Solar System The sun has strong force of attraction. Due to this strong force of attraction, many heavenly bodies remain near to the sun as its family members. A group of eight planets and their satellites, comets, asteroids, etc. which round the sun is called solar system. The sun is the head of the solar system. The eight planets present in the solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Fig: Solar system Fig: Sun The sun is an ultimate source of energy on the earth’s surface because all types of energy are directly and indirectly depend upon the sun. MEMORY TIPS
Modern Concept Science and Technology Book 5 219 Planets Those heavenly bodies which revolve around the sun in their own elliptical orbit are called planets. Planets do not produce their own light. But they reflect the light coming from the sun. So, they are invisible in the day and visible in the night. There are eight planets in the solar system. On the basis of increasing distance from the sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Mercury Mercury is the nearest planet from the sun. It is also the smallest planet. The surface of the mercury that faces the sun is very hot and the surface that is away from the sun is very cold. It is a rocky planet like earth but it has no atmosphere. Venus Venus has atmosphere with large amount of carbon dioxide. Carbon dioxide traps heat of the sun and makes it very hot. Venus is the hottest and brightest planet in the solar system. It is also a rocky planet like earth. Earth The earth is only living planet of the solar system. The earth has abundant air, water, soil and favorable temperature for living organisms to grow and survive. Presence of large oceans in the earth makes it to look blue from space. So, it is also called a blue planet. Pluto crosses the orbit of Neptune. So, now it is not considered as a planet. MEMORY TIPS Fig: Mercury Mercury and Venus do not have satellites. MEMORY TIPS Fig: Venus Venus is the closest planet to the earth. MEMORY TIPS Fig: Earth The earth has a natural satellite called moon. MEMORY TIPS
220 Modern Concept Science and Technology Book 5 Mars Mars is also a terrestrial planet like earth. It has a thin atmosphere. Scientists have already found water in the form of ice in Mars. Mars looks red in colour due to the presence of red coloured rocks called limonite. After the earth, Mars is the most studied planet in the solar system. Due to its physical conditions, scientists are exploring Mars for possibility of human life. Jupiter Jupiter is the largest planet in the solar system. It is the brightest planet after Venus. It is a gaseous planet. Gases like hydrogen and helium make its atmosphere. It also has the rings made up of clouds and gases. It looks pale in colour. Saturn Saturn is the most beautiful planet in the solar system. It looks beautiful due to presence of rings made up of glowing gases, dusts and rocks. It is also a gaseous planet. It is the largest planet after Jupiter. Uranus Uranus is also the planet with rings. But the rings of Uranus are not as glowing as of Saturn. Uranus is a cold planet because its outer layer is formed from the ice. So, it is also called icy planet. It has atmosphere of hydrogen and helium gas. Neptune Neptune is the farthest and the coldest planet in the solar system. It is also an icy planet. Neptune is so far that it is not visible by naked human eyes. Fig: Mars Mercury, Venus, Earth and Mars are called terrestrial planets because they are made up of soil and rocks. MEMORY TIPS Fig: Jupiter Fig: Saturn Fig: Uranus Fig: Neptune
Modern Concept Science and Technology Book 5 221 ACTIVITY 1 Wake up early in the morning before the sun rise. If the sky is clear, you can see a planet bright like stars in the sky but not as moon. Observe it properly. Again look at the clear sky after the sun sets during evening. You can see another planet bright as star but not as moon. What do you guess the planet is? ACTIVITY 2 Cut a paper into eight equal pieces and write the name of a planet in each of the piece. Fold each of the piece and ask eight students randomly to pick up one piece for each. The students should say a unique feature of that planet named in their piece. Stars The bright twinkling heavenly bodies which produce their own light continuously are called stars. Moon and some planets also shine in the sky. But they cannot produce their own light. They reflect the light coming from the sun. Stars produce their own light due to the chemical reaction called nuclear fusion. Stars are the burning balls of the gases. They produce continuous heat and light. They are very large objects in the universe in comparison to the planets. But they look very small because they are very far from the earth. The nearest star from the earth is the sun. The sun is a medium-sized star. Stars cannot be seen in the day because the light of the sun dominates the light of the star. The light now we see coming from the stars had released millions of years ago from their surface. The nearest star from the sun is Proxima Centauri, which is extremely far from the earth. Fig: Stars If there will be another star as large as and as far as the sun, the temperature of the earth would becomes so hot that no living things can live. MEMORY TIPS
222 Modern Concept Science and Technology Book 5 Satellites Satellites are the heavenly bodies or objects which revolve round the planet in their own orbit. There are two types of satellites. They are natural satellites and artificial satellites. All the planets except Mercury and Venus have their own natural satellites. Jupiter has the largest number of natural satellites. Artificial satellites are launched for communications and other scientific purposes. There are hundreds of artificial satellites revolving round the earth. Moon The moon is the only natural satellite of the earth. It revolves round the earth in its own orbit. Moon is the nearest heavenly body from the earth. It reflects the light coming from the sun. So, it looks bright in the sky. Besides the earth, the moon is the most studied heavenly body. Neil Armstrong (the first person to step on the moon) and Edwin Adrien stepped in the moon in 1969 AD for the first time. Dwarf Planets Some heavenly bodies look round like planets and are not the moons of other planets. They also orbit the sun but they do not lie on the same plane like other planets. Such bodies are called dwarf planets. Thus, the round heavenly bodies which are not moons of other planets and orbit the sun are called dwarf planets. Pluto, Eris, Makemake etc. are some dwarf planets. Except Ceres, other dwarf planets orbit sun from the very edge of solar system. Asteroids Beside planets, our solar system contains small body of rocks containing iron. They orbit the sun. They are smaller than that of planets. They are called asteroids. Thus, the heavenly bodies which are found in between Natural satellite (Moon) Artificial satellite Fig: Satellites Fig: Dwarf planets
Modern Concept Science and Technology Book 5 223 the orbits of Mars and Jupiter are called asteroids. Fig: Asteroids Fig: A meteoroid in earth's atmosphere Meteors, Meteorites and Meteoroids The lump of rocks and metals which are smaller than asteroids and found in the solar system are called meteoroids. They are found scattered over the solar system. When a meteoroid enters into the atmosphere of the planet, it burns up and we can see it as a stripe of light. Meteoroids that burnt in the atmosphere of a planet are called meteors. If the meteoroids do not burn completely in the atmosphere of the planet and reach to the surface of the planet, they are called meteorites. Comet The coma shaped heavenly bodies made up of ice, rock and metals which revolve round the sun in an elliptical orbit are called comets. For example encke, halley, shoemaker levy, etc. HOT SKILL HIGHER ORDER THINKING SKILL 1. Which of the following statement is correct? a. Sun provides energy for the planets in the solar system. b. The moon is a natural satellite of the earth. c. Earth is a terrestrial planet while Jupiter is a Jovian (gasesous) planet. d. All of above Answer: The option 'd' is correct. 2. Define satellites with an example. Satellites are the heavenly bodies or objects which revolve round the planet in their own orbit. Moon is an example of satellite of the earth.
224 Modern Concept Science and Technology Book 5 3. Why Venus is the hottest planet in the solar system? The atmosphere of Venus is rich in carbon-dioxide gas that traps heat energy. Due to this reason, venus is the hottest planet in the solar system. 4. What makes planets to revolve round the sun? The gravitational pull (pulling force) of the sun makes planets to revolve round the sun. 5. Differentiate between the stars and planets Stars Planets 1. Stars produces their own heat and light energy. 1. Planets cannot produce their own heat and light. 2. Stars are made up of gases. Examples are Sun, Proixma centauri etc. 2. Some planets are made up of rocks while some are made up of gases. Examples are Earth, Jupiter, etc. 33 STEPS STEPS EXERCISE EXERCISE STEP1 1. Tick (√) the correct statements and cross (x) the false ones. a. The sun is the head of the solar system. b. Mars is the hottest planet. c. Ceres is a man-made satellite. d. Artificial satellites revolve round the earth. e. The sun is a medium-sized star. f. Jupiter has more natural satellites than the earth. 2. Fill in the blanks with appropriate words. a. The pulling force of the ______makes planets to revolve round it. b. The __________ is also known as blue planet. c. The ______________is the nearest star form the earth. d. ____do not have their own light but reflect the light from the sun.
Modern Concept Science and Technology Book 5 225 3. Match the following: a. Sun • Natural satellite b. Earth • Full moon c. Moon • Nearest star to the earth d. Purnima • Living planet 4. Give one word answer for the following. a. The head of the solar system b. The natural satellite of the earth c. Heavenly body revolving round the sun in their own orbit d. Bright balls of the fire twinkling in the sky e. The time taken by the earth to complete a single revolution around the sun. STEP2 5. Differentiate between: a. Planets and stars b. Natural satellites and artificial satellites c. Comets and Asteroids d. Sun and earth e. Earth and moon 6. Give reasons: a. Earth is known as living planet. b. Stars twinkle in the sky. c. Mars is also known as red planet. d. Artificial satellites are launched in the space. e. Mercury, Venus, Earth and Mars are called terrestrial planets. f. Pluto looks like planet but it is known as dwarf planet. 7. Name the planets. a. Morning and evening star b. Hottest planet c. Planet that looks red in colour d. Only the living planet e. Gaseous planet with beautiful rings
226 Modern Concept Science and Technology Book 5 f. The largest planet g. The smallest planet h. The farthest planet from the sun i. The nearest planet from the earth j. The nearest planet from the sun k. Planets with no satellites 8. Name the figure shown below. a. b. STEP3 9. Answer the following questions. a. Define solar system. How many planets are there? b. What is sun? Why is it called head of the solar system? c. What causes planet to revolve round the sun? d. Name eight planets on the basis of increasing distance from the sun. e. Write three features of each planet of the solar system. f. Write down short note about stars. g. What are satellites? Write down their types. h. What are asteroids, comets, meteors, meteorites and meteoroids? 10. Draw a well labelled diagram for the solar system.
Modern Concept Science and Technology Book 5 227 Key terms and terminologies of the unit 1. Nebula : A nebula is a vast interstellar cloud of gas and dust. 2. Rotation of the earth : Rotation refers to the anti-clockwise spinning of the earth on its axis. It is also called diurnal motion of the earth. 3. Revolution of the earth:The orbiting of the earth around the sun is called revolution. It is also called annual motion of the earth. 4. Day and night : The time duration during which the earth faces the sun while rotating on its axis is called day and the time duration during which the earth faces away from the sun is called night. 5. Perihelion : The point in the earth’s orbit nearest to the sun is called perihelion. 6. Aphelion : The point in the earth’s orbit farthest from the sun is called aphelion. 7. Solstice : A solstice is an astronomical event that occurs twice each year (on June 21 and December 22) when the tilt of the earth’s axis is most oriented towards or away from the sun. It is marked by the longest day and the shortest day. 8. Equinox : The astronomical event that occurs twice each year (on March 21 and September 23), when the earth’s axis is tilted neither towards nor away from the sun, making day and night of approximately equal duration is called equinox. 9. Sidereal month : The time taken by the moon to complete one revolution around the earth is called sidereal month. It is of 27.3 days. 10. Synodic month : The time interval between two successive full moon days or two new moon days is called synodic month. It is of about 29.5 days. Sequence of Curriculum Issued by CDC Revolution of earth and its effect Revolution of moon Phases of moon UNIT Motion of the Earth and the Moon 8.2 Estimated teaching periods Theory Practical 8 2 Neil Armstrong was an astronaut of National Aeronautics and Space Administration (NASA) of United States of America. He was born in 1930 and died in 2012. Neil Armstrong was the first man to set foot on the surface of the moon. Along with Buzz Aldrin and Michael Collins, Neil Armstrong reached to the moon. Apollo 11 (spacecraft) was the spacecraft that was used by them. Neil Armstrong About the Scientist
228 Modern Concept Science and Technology Book 5 11. Phases of the moon : The different shapes of the illuminated portion of the moon as seen by an observer on the earth are called phases of the moon. They change cyclically as the moon orbits the earth. 12. New moon : A phase of the moon when the reflected light from its surface does not reach on the earth and hence moon is not visible is called new moon. 13. Full moon : A phase of the moon when the reflected light from its full face reach the earth and hence moon is completely visible is called full moon. 14. Waxing crescent : The phase of the moon in increasing order of brightness from new moon, when less than half of its face gets illuminated is called waxing crescent. 15. Waxing gibbous : The phase of the moon in increasing order of brightness from new moon, when more than half of its face gets illuminated is called waxing gibbous. 16. Waning gibbous : The phase of the moon in decreasing order of brightness from full moon, when less than half of its face gets darkened is called waning gibbous. 17. Waning crescent : The phase of the moon in decreasing order of brightness from full moon, when more than half of its face gets darkened is called waning crescent. Introduction Space is the vast region that lies beyond the atmosphere of the earth including all the celestial bodies. Even scientists are unable to define the limit of the space. In this space, uncountable number of celestial bodies are present. These celestial bodies form the clusters of different shapes and sizes called galaxies. Our solar system is a small portion of the Milky Way galaxy. In the solar system there are eight planets and their satellites, comets, meteors, meteorites, asteroids, etc. In the solar system, life exists only on the the earth. Scientists always wondered to understand the formation of the solar system and the earth. They proposed various hypotheses regarding the formation of the earth. But none of the hypothesis has been universally accepted yet. However, the age of the earth is estimated to be 4.5 billion years. Position of the Earth with Respect to the Sun The earth shows two types of motions. They are rotation and revolution. Earth rotates on its axis and revolves on an orbit. Axis of the earth is an imaginary straight line perpendicular to its equatorial plane and passing through centre. The earth’s orbit around the sun is not completely circular, but it is an oval or elliptical. Thus, orbit of the earth is an elliptical path on which it revolves around the sun.
Modern Concept Science and Technology Book 5 229 Rotation refers to the anti-clockwise spinning of the earth on its axis. It is also called diurnal motion. One rotation takes about twenty four hours and is called a mean solar day. The orbiting of the earth around the sun is called revolution. It is also called annual motion of the earth. One revolution of the earth takes 365.25 days. Fig: Earth revolves round the sun The orbital plane is a two-dimensional flat surface on which the earth revolves around the sun. The earth’s axis is not perpendicular to the orbital plane of the earth. It makes an angle of 66.50 with the orbital plane of the earth. This tilting causes variation in intensity and duration of the sunlight reaching to the earth. The most prominent effects of tilting of the earth are given below: a. The four seasons in a year are caused by the tilt of the earth’s axis as it orbits the sun. b. Tilting of the earth causes different climate in the different places of the earth. c. Due to tilting of the earth, the duration of days and nights are not always equal except in equatorial areas. d. Due to tilting of the earth, the point and time of the sun rise and sun set is different. e. Variation in the solar altitude (height of the sun from the earth at noon) is due to the tilting of the earth’s axis.
230 Modern Concept Science and Technology Book 5 Differences between orbital plane of the earth and axis of the earth SN Orbital plane of the earth SN Axis of the earth 1 The orbital plane of the earth is a two-dimensional flat surface on which it revolves around the sun. 1 Axis of the earth is an imaginary line perpendicular to its equatorial plane and passing through centre. 2 It is a thin elliptical disk shaped. 2 It is a straight line. Days and Nights The sun is a major source of light on the earth. As, the earth spins continuously in its axis, at any time half of the surface of the earth faces towards the sun and half of its surface faces away from the sun. The time duration during which the earth faces the sun while rotating on its axis is called day and the time duration during which the earth faces away from the sun is called night. As the earth takes 24 hours to complete a rotation, a complete day is of nearly 12 hours day time and 12 hours night time. But, the days and nights are not equal due to tilting of the earth. Thus, the continuous rotation of the earth on its axis is the cause of day and night on the earth. FACTS WITH REASONS Why does variation occur in day time and night time throughout a year? The earth’s axis is not perpendicular to the orbital plane of the earth. It makes an angle of 66.5° with the orbital plane of the earth. This tilting causes variation in the duration of the light received by the earth. So, variation occurs in day time and night time throughout a year. Change in seasons The earth revolves around the sun in an elliptical orbit. While revolving around the sun in an elliptical orbit, the earth reaches at different distance from the sun. The point in the earth’s orbit nearest to the sun is called perihelion. At this point, the earth is about 147.3 million km away from the sun. It occurs on January 3. The point farthest from the sun is called aphelion. At this point, the earth is about 152.1 million km away from the sun. It occurs on July 4. Fig: Day and night
Modern Concept Science and Technology Book 5 231 The elliptical orbit causes variation of the earth’s distance from the sun. Yet, this phenomenon is not responsible for the seasons on the earth. The tilting of the earth’s axis is the major cause of change in season. Seasons are of four major types. They are: a. Summer season: In the Northern Hemisphere, summer season officially begins on June 21 and ends on September 23. b. Autumn season: In the Northern Hemisphere, autumnal season officially begins on September 23 and ends on December 22. c. Winter season: In the Northern Hemisphere, winter season officially begins on December 22 and ends on March 21. d. Spring season: In the Northern Hemisphere, spring season officially begins on March 21 and ends on June 21. The seasons in the Southern Hemisphere are the opposite of those in the Northern Hemisphere. That is, the autumnal season in the Northern Hemisphere is the spring season in the Southern Hemisphere and the summer season in the Northern Hemisphere is the winter season in the Southern Hemisphere. The change in season in the Northern Hemisphere and Southern Hemisphere is described below in solstice and equinox. Solistice The Northern Hemisphere is tilted toward the sun in June and away from the sun in December. Due to this reason, the sun heats up more to the Northern Hemisphere in June and Southern Hemisphere in December. Nepal lies in the Northern Hemisphere. So, in the Northern Hemisphere, it is summer in June and winter in December. A solstice is an astronomical event that occurs twice each year (on June 21 and December 22) when the tilt of the earth’s axis is most oriented towards or away from the sun. It is marked by the longest day and the shortest day. a. Summer solstice/ beginning of summer season: In Northern Hemisphere, summer solstice occurs when the earth’s axis tilts towards the sun, or the Northern Hemisphere, is most inclined toward the sun.
232 Modern Concept Science and Technology Book 5 Thus, on June 21 (around Ashar 8), the Northern hemisphere is most inclined towards the sun and receives solar radiations for maximum duration. This is called summer solstice in the Northern Hemisphere. On this day there is longest day and shortest night in the Northern Hemisphere. On summer solstice, the sun’s rays perpendicularly strike the Tropic of Cancer (23.5o north of the Equator). Summer solstice is often referred to as Midsummer. But it is just opposite in case of the Southern Hemisphere. There is winter solstice, or the shortest day and longest night on June 21 in the Southern Hemisphere. b. Winter solstice/ beginning of winter season: In Northern Hemisphere, winter solstice occurs when the earth’s axis tilts away from the sun, or the Northern Hemisphere is most inclined away from the sun. Thus, on December 22 (around Poush 7), the Northern hemisphere is most inclined away from the sun and receives solar radiations for minimum duration. This is called winter solstice in the Northern Hemisphere. On this day there is shortest day and longest night in the Northern Hemisphere. On winter solstice, the sun’s rays perpendicularly strike the Tropic of Capricorn (23.5o south of the Equator). Winter solstice is often referred to as Midwinter. But it is just opposite in case of the Southern Hemisphere. There is summer solstice, or the longest day and shortest night on December 22 in the Southern Hemisphere. Equinox In March and September, earth’s Northern and Southern Hemispheres receive the sun’s rays almost equally and the length of night and day are nearly equal. The astronomical event that occurs twice each year (on March 21 and September 23), when the earth’s axis is tilted neither towards nor away from the sun, making day and night of approximately equal duration is called equinox. i) Autumn equinox: On September 23 (around Ashwin 7), the sun’s rays perpendicularly strike the Equator. On this day night and day are of approximately equal length all over the earth. This is called autumn equinox in the Northern Hemisphere. But there is spring equinox in the Southern Hemisphere on September 23. In autumn season the weather is neither so cold as in winter, nor so hot as in summer. ii) Spring equinox (Vernal equinox): On March 21 (around Chaitra 8), the sun’s rays perpendicularly strike the Equator. On this day night and day
Modern Concept Science and Technology Book 5 233 are of approximately equal length all over the earth. This is called spring equinox in the Northern Hemisphere. But there is autumn equinox in the Southern Hemisphere on March 21. In spring season the weather is neither so cold as in winter, nor so hot as in summer. 21 March equinox Earth's orbit around the sun 23 September equinox Northern fall Southern spring 22 December solstice Northern winter Northern spring Southern fall Southern summer Southern winter Northern summer 21 June solstice A D C B Fig: Change in season FACTS WITH REASONS Why do seasons change on the earth? Change in seasons takes place on the earth due to its tilted axis and revolution around the sun. Phases of Moon The moon is only natural satellite of the earth. It is a non-luminous body. It looks bright because it reflects sunlight towards the earth. We see the portion of the moon that reflects sunlight towards the observers on the earth. Moon revolves around the earth in its orbit. The time taken by the moon to complete one revolution around the earth is called sidereal month. It is of 27.3 days. As moon revolves around the earth, the earth is also revolving around the sun. Due to this reason, the sunlight falls on the moon at different angles. This creates different shapes of the moon while observing from the earth. Thus, the different shapes of the illuminated portion of the moon as seen by an observer on the earth are called phases of the moon. They change cyclically as the moon orbits the earth. Four major phases of the moon are first quarter, full moon, last quarter and half-moon. The moon takes 29.5
234 Modern Concept Science and Technology Book 5 days to come in the same phase after complete revolution. This is called synodic month. Therefore, the time interval between two successive full moon days or two new moon days is called synodic month. It is of about 29.5 days. The difference between sidereal and synodic months causes delay in the rising of the moon everyday by 50 minutes. Different phases of the moon are described below: 1. Earth’s moon is the fifth largest satellite of the solar system. 2. The moon orbits the Earth once every 27.322 days. It takes approximately 27 days to rotate once on its axis. Thus, we always see the same face of the moon as it rotates on its axis at nearly the same time as it revolves around the earth. MEMORY TIPS Fig: Phases of the moon a. New moon: As the time of rising of the moon delays 50 minutes per day, after 15 days, the rising time of both the sun and the moon becomes the same. That is, the moon and the earth both come in the same side from the earth. In other words, the moon comes in between the sun and the earth. The sunlight falling on the moon reflects away from the earth. People on the earth do not receive the reflected light from the moon. At this time, we cannot see the moon from the earth. A phase of the moon when the reflected light from its surface does not reach on the earth and hence moon is not visible is called new moon b. Waxing crescent: The order of brightness gradually increases after new moon. The phase of the moon in increasing order of brightness from new moon, when less than half of its face gets illuminated is called waxing crescent. c. First quarter: When the moon is perpendicular to the earth and the sun, the sunlight from half of its part reflects towards the earth. The phase of the moon in increasing order of brightness from new moon, when half of its face gets illuminated is called first quarter.
Modern Concept Science and Technology Book 5 235 d. Waxing gibbous: When the moon moves further on its orbit we see more than half bright part of the moon. The phase of the moon in increasing order of brightness from new moon, when more than half of its face gets illuminated is called waxing gibbous. e. Full moon: Almost after 15 days from the new moon, the moon rises just after the sun set. That is the sun and the moon come in opposite side of the earth. The sunlight falling on the moon reflects towards the earth. People on the earth receive the reflected light from the moon. At this time, we can see the moon. A phase of the moon when the reflected light from its full face reach the earth and hence moon is completely visible is called full moon. f. Wanning gibbous: After full moon, the bright face of the moon goes on decreasing in the coming days. The phase of the moon in decreasing order of brightness from full moon, when less than half of its face gets darkened is called waning gibbous. g. Third quarter: After waning gibbous, the moon becomes perpendicular to the sun and the earth. At this condition, the bright part decreased to half. The phase of the moon in decreasing order of brightness from full moon, when half of its face gets darkened is called third quarter. h. Waning crescent: The phase of the moon in decreasing order of brightness from full moon, when more than half of its face gets darkened is called waning crescent. Finally, the moon comes in between the sun and the earth again and the moon becomes totally dark. It is again called new moon. In this way, the phases of the moon change cyclically within a synodic month as the moon orbits the earth. The duration of increasing order of brightness of the moon after new moon to the full moon is called bright half (Shukla Pakshya). While the duration of decreasing order of brightness of the moon after full moon to the new moon is called dark half (Krishna Pakshya).
236 Modern Concept Science and Technology Book 5 FACTS WITH REASONS How is sidereal month different from synodic month? Sidereal month is the duration of revolution of the moon. However, as the moon revolves around the earth, the earth also moves ahead in its own orbit around the sun. So, some extra time is required for the moon to come in its own phase. So, there is difference between the synodic and sidereal month. Differences between new moon and full moon. SN New moon SN Full moon 1 During new moon, the moon is not seen at all. 1 During full moon, the bright face of the moon is seen completely. 2 Solar eclipse occurs in a new moon day. 2 Lunar eclipse occurs in a full moon day. FACTS WITH REASONS Why can’t we see moon in a new moon day? We cannot see moon in a new moon day because moon does not reflect sunlight toward the earth during new moon. HOT SKILL HIGHER ORDER THINKING SKILL 1. What do you mean by the axis of the earth? An axis is an imaginary line perpendicular to its equatorial plane and passing through the centre of the earth. 2. What are the phases of the moon? Write down the major phases of the moon. The different shapes of the illuminated portion of the moon as seen by an observer on the earth are called phases of the moon. Four major phases of the moon are new moon, first quarter, full moon, and last quarter. 3. Write down any five major reasons to support evolution of life on the earth. The major reasons for evolution of life on the earth can be listed below: i. The earth has suitable amount of oxygen, carbon dioxide, nitrogen, etc. ii. It has sufficient amount of water. iii. It has suitable temperature.
Modern Concept Science and Technology Book 5 237 iv. Its atmosphere has suitable amount of greenhouse gases. v. The earth is covered by ozone layer to protect from the harmful solar radiations. 4. What are major effects of tilting of the earth by 66.5 degrees? The most prominent effects of tilting of the earth are given below: i. Tilting of the earth causes occurrence of four seasons in a year. ii. Tilting of the earth causes different climate in the different places of the earth. iii. Due to tilting of the earth, the days and nights are not always equal except in equatorial areas. 5. Differences between bright half and dark half. Differences between bright half and dark half are: S.N. Bright half S.N. Dark half 1 The time take by the moon from new moon to full moon is called bright half. 1 The time take by the moon from full moon to new moon is called dark half. 2 In this condition the brighter face of the moon goes on increasing. 2 In this condition the brighter face of the moon goes on decreasing. 6. Differences between summer season and winter season. Differences between summer season and winter seasons are: S.N. Summer season S.N. Winter season 1 Summer season is characterized by the long days and short night. 1 Winter season is characterized by the long night and short days. 2 In this season, we feel hot. 2 In this season, we feel cold. 33 STEPS STEPS EXERCISE EXERCISE STEP1 1. Fill in the blanks with appropriate words. a. Availability of __________ gas is the major feature of the earth so that it can sustain living beings on it. b. ___________ of the earth is responsible for the change in season. c. The days and nights are equal on _________ and ____________ d. The synodic month has duration ____________ days and sidereal month has ____________ days.
238 Modern Concept Science and Technology Book 5 2. Write True for the correct and False for the incorrect statements. a. Oxygen is a life supporting gas. b. Tilting of the earth is responsible for difference in duration of days and nights. c. June 21 is the winter solstice in southern hemisphere. d. The next phase of the moon after waning crescent is full moon. 3. Select the best answer from the given alternatives. a. What is the estimated age of the earth? i. 1.5 billion years ii. 3.5 billion years iii. 4 billion years iv. 4.5 billion years b. Every day the rising of the moon delays by: i. 20 minutes ii. 30 minutes iii. 50 minutes iv. 60 minutes c. Which is the longest day in the Northern Hemisphere? i. December 22 ii. June 21 iii. April 21 iv. May 21 d. What is the angle of tilting of the earth with respect to its orbital plane? i. 90° ii. 23.5° iii. 66.5° iv. 45.5° e. The moon revolves around the earth in ... i. 29.5 days ii. 27.33 days iii. 25.9 days iv. 30 days 4. Match the following. a. Bright half i. 27.3 days b. Dark half ii. new moon to full moon c. Longest night iii. 29.5 days d. Longest day iv. full moon to new moon e. Synodic month v. asar 8 f. Sidereal month vi. posuh 7
Modern Concept Science and Technology Book 5 239 STEP2 5. Answer the following questions in one word. a. Write down the name of the planet with life on it. b. Which day is the longest day in the Northern Hemisphere? c. Name the nearest heavenly body to the earth. d. How long is the bright half? e. What causes day and night? 6. Write any two differences between: a. Dark half and bright half b. Summer solstice and winter solstice c. Synodic month and sidereal month d. Waxing gibbous and waning gibbous 7. Give reasons. a. We cannot see moon in a new moon day. b. There is a difference between the synodic and sidereal month of the moon. c. Season changes in the earth. d. Days and nights are not always of equal duration. 8. Observe the figure and name the phases of the moon. a b c d e f g h
240 Modern Concept Science and Technology Book 5 STEP3 9. Answer the following questions. a. What is axis of the earth? Write the effects of tilting of axis of the earth. b. What is orbital plane? Explain how do seasons change on the earth. c. Explain the phases of the moon with a labelled diagram. d. When do the following occur in the Northern Hemisphere? i. Vernal equinox ii. Winter solstice iii. Autumnal equinox iv. Summer solstice 10. Study the given diagram and answer the following: A B a. Which type of motion of the earth is shown in the diagram? b. Write one effect of such motion. c. Write the name of season A and B in the Northern Hemisphere.