Modern Concept Science and Technology 5 New

Modern Concept Science and Technology Book 5 151 Key terms and terminologies of the unit 1. Energy : The capacity of doing work is called energy. 2. Sources of energy : Things or places from where we get energy are called sources of energy. 3. Heat : Heat is a form of energy, which gives the sensation of warmth. 4. Conservation of energy : Using energy and sources of energy wisely and economically is called conservation of energy. Introduction The capacity of doing work is called energy. All living organisms need energy to live. We get energy from food. The different fossil fuels like coal, petrol, diesel give energy to run vehicles and industries. Cooking gas, kerosene, firewood give energy to cook food. Running water gives energy to run water mills and to produce electricity. Solar energy and wind energy also produce electricity. Electricity is used in various activities like cooking food, lighting, warming rooms, running industries, running vehicles, etc. Human beings need different types of energy to live. Sequence of Curriculum Issued by CDC  Effects of heat in state and volume of matter  Advantages and disadvantages of effects of heat UNIT Effects of Heat on Matter 6.2 Estimated teaching periods Theory Practical 8 2 James Prescott Joule was an English physicist. He wasborn in 1818 and died in 1889. He established that the various forms of energy; mechanical, electrical, and heat, are basically the same and can be changed one into another. Thus, he formed the basis of the law of conservation of energy, the first law of thermodynamics. The unit of energy Joule is honoured after his name. James Prescott Joule About the Scientist

152 Modern Concept Science and Technology Book 5 Fig: Sources of Energy Different forms of energy There are different forms of energy. They are heat energy, light energy, sound energy, magnetic energy, chemical energy, solar energy, mechanical energy, magnetic energy, nuclear energy. Fig: Forms of energy Sources of energy Things or places from which we get energy are called sources of energy. Sun, firewood, fossil fuels, magnet, musical instruments, battery, friction, nucleus of atoms are some sources of energy. Among them, the sun is the ultimate source of energy on earth because all the other sources of energy are derived from the sun. It is a direct source of heat and light energy. Heat energy Heat is a form of energy which gives the sensation of warmth. The sun is a major source of heat energy on earth. Firewood, The materials which are used to produce energy are called fuels. MEMORY TIPS Sun LPG Burning fire

Modern Concept Science and Technology Book 5 153 heater, coal, LP gas, diesel, petrol, etc. are other sources of heat energy. Heat energy is used for cooking food, running vehicles, operating engines in the factories, drying clothes, drying food grains, etc. Human body also needs heat energy. Food provides heat energy to our body and makes us warm. Effects of heat on matter Heat shows different effects on matter. Some of the effects of heat are listed below. i. Heat increases the length of an object. ii. Heat increases the volume of an object. iii. Heat changes the shape of the body. iv. Heat changes the state of a matter. v. Heat increases the temperature of a body. Change in state of matter Heat energy can change the state of matter. Ice is a solid. When we heat ice, it changes into water. Water is a liquid. When we again heat water, it changes into water vapour. Water vapor is a gas. Similarly, when we cool water vapor, it changes into water droplets. When water is further cooled, it freezes into ice. In this way, heat changes the state of the matter. We usually see that wet clothes get dry due to solar heat. The solar heat changes water into water vapor and makes the clothes dry. Similarly, food grains also get dried due to sunlight. Fig: Change in the state of matter

154 Modern Concept Science and Technology Book 5 ACTIVITY 1 To show that heat increases the length of an object Take a thin copper wire and tie a piece of stone with it. Tie the wire on a horizontal rod and hang as shown in the given figure. The stone should be very near to the ground, but it should not touch the ground. Heat the copper wire at any point for some time and observe what happens. Observation After some time, the stone touches the ground. Conclusion When we heat the copper wire, it expands and the length increases. As a result, the stone touches the ground. ACTIVITY 2 To show that heat increases the volume of a body Take a glass bottle and keep some water in it. Add some drops of red ink in it. Now, it is red colored. Mark the water level in the glass bottle. Cover the mouth of the glass bottle with a tight cork. Keep the glass bottle in a hot water trough. Observation The water in the glass bottle becomes hot, and the level of water increases above the marked level. Conclusion When matter gets heated, its molecules move farther away from each other. This increases the volume of the matter.

Modern Concept Science and Technology Book 5 155 ACTIVITY 3 To show that heat changes the shape of the object Take a bottle which has a narrow mouth. Cover the mouth of the bottle using a big balloon. Take a trough with boiled water in it. Keep the bottle in the hot water trough for some time. What do you observe? Observation You can observe the balloon inflates a little when kept in a trough with hot water. Conclusion Hot water gives heat to the air inside the bottle. Hot air rises up and fills into the balloon. Then, the balloon inflates. This activity shows that heat changes the shape of an object. ACTIVITY 4 To show that heat changes the state of matter Take some ice cubes from the fridge. Put them in a beaker. Heat the beaker in the burner for a minute. Observe what happens to the ice cubes. Observation When we heat the beaker, the ice cubes get heated. After heating, the molecules of ice move away from each other. This changes ice into water. When we heat water further, it changes into water vapor and rises up in the sky. Conclusion This activity shows that heat changes the state of matter.

156 Modern Concept Science and Technology Book 5 ACTIVITY 5 To show that heat increases the temperature of matter Take normal water in a beaker. Measure its temperature and record it in your exercise book. Heat the beaker using a Bunsen burner for about two minutes. Now, measure the temperature of the water. What difference do you observe? Observation The temperature of the cold water is less. The temperature of the warm water is more. Conclusion This activity shows that heat increases the temperature of matter. Advantage and Disadvantage of Heating Effect Effect of heat over matter have different advantages in our daily life. Some of the advantages are mentioned below. 1. It helps the food cooked properly. 2. Stopper of jammed bottle can be expanded using hot water and removed. 3. We can measure the temperature of any object using thermometer. 4. Travelling on hot air balloon is possible. 5. It helps fixing iron rim with the wooden wheel. 6. Smoke moves upward in the sky. 7. Water cycle occurs due to this effect. 8. Metals can be melted or reshaped according to our need. Effect of heat over matters is always not beneficial to us. Some of the disadvantage of heating effect are: 1. Overflow of milk and other fluids while heating causes loss. 2. We need refrigerator to avoid change of ice to water.

Modern Concept Science and Technology Book 5 157 3. It causes change in the composition of matter by resulting chemical change in them. 4. Rubber expansion joints are to be used in bridges to avoid expansion. 5. Cracking of a thick glass tumbler due to hot water. 6. Heat can cause the electric wires in electric poles to sag during summer season. Applications of heat in our daily life i. Heat keeps our body warm. A healthy human body has a constant temperature of about 98.6o Fahrenheit. ii. We need heat for cooking food. Different sources of heat like firewood, solar energy, electricity, kerosene, LP gas, natural gas are used for cooking purposes. iii. We need heat to dry food grains, wet utensils, washed clothes and firewood. Solar energy is mainly used for drying purpose. iv. Heat is used for running automobiles. Petrol, diesel, LP gas are used to run vehicles. Heat is required in industries for their operation. In industries, heat is obtained from various sources like petrol, diesel, kerosene and coal. Conservation of energy Conservation means saving for the future. So, using energy and sources of energy wisely and economically is called conservation of energy. Energy can be conserved by the following ways. i. We should turn off electrical appliances when they are not in use. ii. We should use highly efficient electrical devices as far as possible. For example, use of CFL in place of normal bulbs, use of LED monitor in place of CRT monitors, use of pressure cooker in place of normal utensils.

158 Modern Concept Science and Technology Book 5 iii. Non-renewable sources of energy like petrol, LPG, diesel, coal, kerosene should be used wisely. iv. We should walk or take a cycle for a short distance and use vehicles for only long distances. v. We should encourage gadgets that run on solar energy. For example, solar light, solar cooker, solar water heater, etc. vi. We should use bio-gas as an alternative source of energy for cooking and lighting in place of firewood or electricity. vii. We can use wind energy for lifting water. viii. We should use public transportation in place of private vehicles. HOT SKILL HIGHER ORDER THINKING SKILL 1. Which of the following is the effect of the heat? a. Heat increases the volume of an object. b. Heat changes the state of a matter. c. Heat increases the temperature of the body. d. All of above Heat increases volume and temperature. It also changes state of matter. 2. What type of energy does hydro-electric plant produce? Hydro-electric plant produces electrical energy. 3. Define sources of energy with two examples. The place or objects from which we obtain energy are called sources of energy. Two examples of sources of energy are fuel-wood and sun. 4. Why is the sun known as the ultimate source of energy? Explain with an example. 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. For an example, the hydro-electricity is only possible if water flows. Water cycle governs the flow of water by circulating water between land, ocean and atmosphere. Sun provides the energy for water cycle. Therefore, the sun is considered as the ultimate source of energy.

Modern Concept Science and Technology Book 5 159 5. How does heat change the state of matter? Explain with an example. Heat increases the temperature of the matter. Heat weakens the force of attraction between the molecules. It results change in the state of the matter. For an example, on heating ice, force of attraction of molecules decreases and molecules move far apart. This changes the ice into liquid water. Further heating liquid water, the molecules of water move farther. It farther decreases force of attraction. This results change of water into water vapour. Here, heat changes solid ice into liquid water and to gaseous water vapour. 33 STEPS STEPS EXERCISE EXERCISE STEP1 1. Tick (√) the correct statements and cross (x) the false ones. a. Energy is the capacity of doing work. b. All living things get energy from food. c. Heat cannot change the volume of an object. d. The sun is the major source of energy on earth. e. A simple bulb should be used in place of a CFL one. f. CRT monitor is better than LED monitor. 2. Fill in the blanks with appropriate words: a. The capacity of doing work is called ________________ . b. Living things get energy from _________________ . c. Heat is a form of energy which gives the sensation of _________. d. The full form of LP gas is _______________ . e. Heat energy can change the state of ________________ . f. The major source of heat energy on earth is ____________. g. Water changes into ____________on heating and changes into _________ on cooling. h. _____________increases the temperature of a body.

160 Modern Concept Science and Technology Book 5 3. Match the following: a. Energy i. Conservation of energy b. Heat increases ii. Major source of heat c. States of matter iii. Capacity of doing work d. The sun iv. Solid, liquid and gas e. Wise use of energy v. Temperature 4. Select the best answer from the given alternatives. a. The capacity of doing work is called : i. Energy ii. Pressure iii. Power iv. Force b. Water freezes to ice when : i. Heating ii. Cooling iii. Compressing iv. Expanding c. Which of the following does not need solar energy? i. Solar cooker ii. Pressure cooker iii. Solar panel iv. Solar cell d. When we heat matter, its temperature : i. Decreases ii. Remains constant iii. Increases iv. Depends upon condition e. Which is the main source of energy on earth? i. Wind energy ii. Solar energy iii. Petrol iv. Hydro-power STEP2 5. Write down one difference between: a. Heat and energy b. Solar energy and petrol 6. Give reasons. a. The sun is the ultimate source of energy. b. We need energy.

Modern Concept Science and Technology Book 5 161 c. CFL is better than a normal bulb. d. We should use public vehicles in place of private ones. 7. Which effect of heat do the following figures show? a. b. c. d. e. f.

162 Modern Concept Science and Technology Book 5 8. Answer the following in one word. a. What is the capacity of doing work called? b. Things or places from which we get energy are called c. The form of energy which gives the sensation of warmth is called d. Using energy wisely and economically is called STEP3 9. Answer the following questions. a. Define energy with any two examples. b. What is heat? Write down any three effects of heat. c. What are the sources of energy? Name any three. d. Name three different forms of energy. e. Write any four applications of heat energy in our daily life. f. Write any four ways of saving energy. 10. Describe an activity to show that heat increases the length of a body. 11. How can you show that heat increases the volume of a body? Explain with a figure.

Modern Concept Science and Technology Book 5 163 Key terms and terminologies of the unit 1. Mixture: Amixture is themass which is obtained bymixing two ormore substances in any proportion by weight. 2. Homogeneous mixture: A mixture in which the components are distributed uniformly and they cannot be identified by naked eyes is called a homogeneous mixture. 3. Heterogeneous mixture: A mixture in which the components are not distributed uniformly and they can be identified by naked eyes is called a heterogeneous mixture. 4. Separation of mixture: The process by which the components of a mixture are separated from each other is called separation of mixture. 5. Sedimentation: The process of settling down of heavier components of a mixture at the bottom of the vessel is called sedimentation. 6. Decantation: The process in which a clear liquid is poured into another vessel without disturbing the sediment is called decantation. 7. Sediment: The heavier and insoluble solid particles deposited at the bottom of a beaker after sedimentation are called sediment. 8. Filtration: The process of separating a mixture in which the components of the mixture are separated by using muslin cloth or filter paper is called filtration. Sequence of Curriculum Issued by CDC  Introduction to mixtures  Composition of mixtures (solid and solid, solid and liquid, liquid and liquid, liquid and gas and gas and gas)  Homogeneous and heterogeneous mixtures  Methods of separation of mixtures (hand picking, sedimentation and decantation, winnowing, sieving and filtration) UNIT Mixture 6.3 Estimated teaching periods Theory Practical 8 2 Satyendra Nath Bose was an Indian mathematician and physicist. He was born in 1894, and died in 1974, in India. In collaboration with Albert Einstein, he proposed a new state of matter called Bose-Einstein Condensate from cooled gas atoms. BECs have also been used to create atomic lasers, atomic clocks and gravitational, rotational or magnetic sensors with excellent sensitivity. Satyendra Nath Bose About the Scientist

164 Modern Concept Science and Technology Book 5 9. Filtrate: The clear liquid collected after filtration is called a filtrate. 10. Residue: The mass of solid particles collected on the filter paper during filtration is called residue. 11. Winnowing: The method of separating a mixture of light and heavy solid particles with the help of wind is called winnowing. 12. Sieving: The method of separating a mixture of solid particles of different size by using a sieve is called sieving. 13. Magnetic separation: The method of separating magnetic substances from non-magnetic substances by using a magnet is called magnetic separation. Introduction In our surroundings, there are many substances which are intermingled with each other. In the atmosphere, different types of gases and dust particles are mixed together. We prepare sugar solution by putting sugar into water. Similar types of many solutions are used in our daily life, such as tea, medicine, drinks, etc. Not only solution but also different types of mixtures are familiar to us. Rice husks in rice, sand in rice, sand in lime, dust particles in air, etc. are some examples of mixture. So, a mixture is the mass which is obtained by mixing two or more substances in any proportion by weight. Composition of mixture We can make mixtures by mixing various components. The main types of mixtures on the basis of mixing components are given below: 1. Solid and Solid: For example, alloys like brass, bronze, steel, etc. 2. Solid and Liquid: For example, sugar solution, salt solution, etc. 3. Solid and Gas: For example, aerosol, smog, etc. 4. Liquid and Liquid: For example, water in milk 5. Liquid and Gas: For example, soft drink, soda water, etc. 6. Gas and Gas: For example, air Components of a mixture The substances which are mixed to form a mixture are called components of a mixture. In a mixture, the mixing components do not lose their identity. Mixture is an impure substance as it is made of two or more kinds of substances. The components of a mixture can be separated to get pure substances. Various methods are applied to separate the components of a

Modern Concept Science and Technology Book 5 165 mixture. In this unit, we will study the different methods of separating mixtures such as filtration, sedimentation and decantation, winnowing, sieving, etc. Types of Mixture Depending on the nature, there are two types of mixtures. They are: a. Homogeneous mixture b. Heterogeneous mixture a. Homogeneous mixture A mixture in which the components are distributed uniformly and they cannot be identified by naked eyes is called homogeneous mixture. For example: sugar solution, salt solution, etc. In a sugar solution, sugar particles are distributed uniformly throughout the water. Similarly, in a salt solution, salt is uniformly distributed in water. FACTS WITH REASONS A sugar solution is called a homogeneous mixture, why? A sugar solution is called a homogeneous mixture because the components are uniformly distributed in it. b. Heterogeneous mixture A mixture in which the components are not distributed uniformly and they can be identified by naked eyes is called a heterogeneous mixture. Rice husks in rice, sand in rice, muddy water, etc. are some examples of heterogeneous mixtures. Differences between homogeneous mixture and heterogeneous mixture: SN Homogeneous mixture SN Heterogeneous mixture 1 In this mixture, components are distributed uniformly. 1 In this mixture, components are not distributed uniformly. 2 We cannot see all the components. For example, salt solution, brass, etc. 2 We can see the components. For example, muddy water, pieces of stones in rice, etc. Sugar solution Sand and water

166 Modern Concept Science and Technology Book 5 Importance of Mixtures Mixtures play a significant role in our daily life as they are prepared for various purposes. The importance of mixtures are given below: i. A mixture of tea leaves, sugar, milk and water is made to prepare tea. ii. A mixture of glucose and water is made for drinking. iii. A mixture of different colours is used in painting. iv. A mixture of cement, sand, water and gravel is used for construction works. v. Medicines are made by mixing various chemicals. vi. Plants absorb various nutrients from the soil in the form of a mixture. Methods of Separating Mixtures A mixture has two or more components. The process by which the components of a mixture are separated from each other is called separation of mixtures. There are several methods of separating mixtures such as filtration, sublimation, distillation, picking, sieving, winnowing, sedimentation and decantation, etc. The application of a particular method depends on the nature and property of the components of a mixture. In this unit, you will learn some common methods of separating mixtures, viz. sedimentation and decantation, filtration, winnowing, sieving and magnetic separation. a. Sedimentation and Decantation Generally, sedimentation and decantation are used to separate the components of heterogeneous mixtures in which one of the two components is heavier than another like sand and water, mud and water, etc. In this method, the heterogeneous mixture is left undisturbed for some time to let the sediment settle at the bottom of the container. Then the clear liquid is gently poured into another vessel without disturbing the sediment. This method is also applied to separate the mixture of two liquids having different density. The process of settling down of heavier components of a mixture at the bottom of the vessel is called sedimentation. Decantation Oil Water Oil

Modern Concept Science and Technology Book 5 167 The heavier and insoluble particles of a mixture are called sediment. The process in which the clear liquid is poured into another vessel without disturbing the sediment is called decantation. ACTIVITY 1 Objective : To separate sand and water from their mixture. Requirement : Two beakers, a glass rod, sand, water Procedure: 1. Prepare a mixture of sand and water by mixing them at any ratio. 2. Leave the mixture undisturbed for some time. 3. Pour the clean water into another vessel gently using a glass rod without disturbing the sediment. Observation : As you keep the mixture undisturbed for a while, the heavier particles slowly settle down at the bottom of the beaker and clear liquid is seen above the sediment. Conclusion : Sediment, i.e. sand is left in one beaker and clear water is collected in another beaker. In this way, components of the mixture are separated by sedimentation and decantation. b. Filtration Insoluble solid particles mixed in a liquid can be separated by passing the mixture through a filter paper, thin cloth or a net of wire, etc. This method is called filtration. The process of separating mixtures in which the components are separated by using a muslin cloth or filter paper is called filtration. In this method, the heterogeneous mixture of solid particles and liquid is separated. For example, a fine net like structure called sieve is used to separate tea leaves from tea before drinking. In filtration, the clear liquid collected after filtration is called filtrate and the solid mass of insoluble particles collected on the filter paper is called residue. Generally, filter paper is used for filtration in a laboratory. Before using the filter paper, it is folded to make a cone as shown in the following figure. Filtration

168 Modern Concept Science and Technology Book 5 Fig: Steps to fold a filter paper into a cone ACTIVITY 2 Objective : To separate mud and water from muddy water. Requirement : Two beakers, glass rod, stand, funnel, filter paper, mud, and water Procedure : 1. Prepare a mixture of mud and water in a beaker. 2. Fold the filter paper into a cone. 3. Put the cone shaped filter paper in the funnel and arrange the apparatus as shown in the given diagram. 4. Pour the mixture in the funnel gently with the help of a glass rod. Observation : You will see the clear droplets of water falling through the stem of funnel into the beaker. The mass of solid particles or residue remains on the filter paper. Conclusion : The mixture of mud and water can be separated by filtration. As a result, the clear water is collected in one vessel and the solid particles, i.e. mud on the filter paper. Muddy water Filter paper Funnel Residue Stand Filtrate FACTS WITH REASONS Salt and water cannot be separated by filtration, why? Salt and water cannot be separated by filtration because it is a homogeneous mixture. Differences between sieving and filtration SN Filtration SN Sedimentation 1 The process in which the components of a mixture are separated by using a muslin cloth or filter paper is called filtration. 1 The process of settling down of heavier components of a mixture at the bottom of the vessel is called sedimentation. 2 Filtration needs filter paper. 2 Sedimentation uses gravity.

Modern Concept Science and Technology Book 5 169 FACTS WITH REASONS Why is filtration used in our kitchen for drinking water? Filtration is used in our kitchen for drinking water because filtration removes insoluble solid impurities from water. c. Winnowing Winnowing is used to separate lighter and heavier components of a heterogeneous mixture. The method of separating a mixture of light and heavy solid particles with the help of wind is called winnowing. Husks from rice, stone particles from rice, etc. can be separated by this method. From the above examples, husk is a lighter component and rice is a heavier component. By winnowing, farmers separate husk from rice in rural areas. d. Sieving In some mixtures, the size of mixing particles differs from each other. In this condition, sieving is used to separate the components of a mixture. In sieving, we use a special type of device called sieve. It contains a large number of pores. The size of all pores in one sieve is about the same. The method of separating the mixture of solid particles of different size by using a sieve is called sieving. In sieving, we keep the mixture on the sieve and shake the sieve gently. The particles which are smaller than the size of pores on the sieve fall down from the sieve and the particles bigger than the size of the pores on the sieve remain on the sieve. This method is used to separate corn and millet, pebbles and sand, wheat and flour, etc. Winnowing Sieving

170 Modern Concept Science and Technology Book 5 Differences between sieving and filtration SN Sieving SN Filtration 1 The method of separating mixtures of solid particles of different size by using a sieve is called sieving. 1 The process of separating mixtures by using a muslin cloth or filter paper is called filtration. 2 The sieve used in this method has larger pores. 2 The filter paper used in this method has smaller pores. e. Magnetic Separation Magnet attracts magnetic substances like iron, nickel, cobalt, etc. Magnetic separation is used to separate magnetic substances from non-magnetic substances. The method of separating magnetic substances from non-magnetic substances by using a magnet is called magnetic separation. In this method, we use a magnet. The magnetic substances are attracted by the magnet. As a result, the nonmagnetic substances and the magnetic substances can be separated from the mixture. FACTS WITH REASONS Magnet is used to separate magnetic substances, why? Magnet is used to separate magnetic substances because magnet can pull magnetic substances. HOT SKILL HIGHER ORDER THINKING SKILL 1. How many types of mixtures are there on the basis of distribution of components? There are two types of mixtures on the basis of distribution of components. They are homogeneous mixture and heterogeneous mixture. 2. In which condition do we use winnowing method of separating mixture? We use winnowing method if the weight of mixing particles differs from each other. Powdered ore Moving belt Magnetic roller Impurities Pure Magnetic separation

Modern Concept Science and Technology Book 5 171 3. Write any four importance of mixtures. Importance of mixtures are: i. A mixture of tea leaves, sugar, milk, water, etc. is used to make tea. ii. A mixture of different colour is used for painting. iii. Plant absorbs various nutrients from the soil in form of a mixture. iv. Medicines are made by mixing various chemicals. 4. Identify the method of separating the following mixtures: i. Wheat and flour ii. Muddy water iii. Wheat and flour: sieving iv. Muddy water: filtration 5. Write any two differences between homogeneous mixture and heterogeneous mixture. Differences between homogeneous mixture and heterogeneous mixture are: S.N. Homogeneous mixture S.N. Heterogeneous mixture 1 A mixture in which the components are distributed uniformly and they cannot be identified by naked eyes is called a homogeneous mixture. 1 A mixture in which the components are not distributed uniformly and they can be identified by naked eyes is called a heterogeneous mixture. 2 Homogeneous mixtures cannot be separated by filtration. Example: glucose and water. 2 Heterogeneous mixtures can be separated by filtration. Example: water and sand. 6. What is winnowing? A method of separating the mixtures of light and heavy solid particles with the help of wind is called winnowing. 7. Define residue and filtrate. The mass of solid particles collected on the filter paper during filtration is called residue. The clear liquid collected after filtration is called filtrate. 8. What is magnetic separation? In which condition do we use magnetic separation? The method of separating magnetic substances from non-magnetic substances by using a magnet is called magnetic separation. We use magnetic separation when magnetic substances are found mixed with nonmagnetic substances.

172 Modern Concept Science and Technology Book 5 33 STEPS STEPS EXERCISE EXERCISE STEP1 1. Fill in the blanks with appropriate words. a. The mass of two or more substances in ____________ ratio makes a mixture. b. Sugar solution is a ____________ mixture. c. ____________is used to separate magnetic substances from the nonmagnetic substances. d. ____________is used to separate bigger and smaller solid particles from the mixture. e. The mass of solid substance collected on the filter paper is called ____________ f. The process of pouring the clear liquid into another vessel without disturbing sediment is called ____________ . 2. Write True for the correct and False for the incorrect statements. a. The mass formed by mixing two or more substances in any ratio is called mixture. b. The mixtures in which the components are uniformly distributed throughout the mixture is called homogeneous mixture. c. Filtration is the process in which the heavier particles of a mixture settle down at the bottom of the vessel. d. The clear liquid collected after the filtration is called residue. e. The mixture of wheat and flour can be separated by winnowing. 3. Select the best answer from the given alternatives. a. Which of the following is a homogeneous mixture?

Modern Concept Science and Technology Book 5 173 i. Salt and water ii. Sand and water iii. Soil and water iv. Sand and salt b. Which of the following is a heterogeneous mixture? i. Salt and water ii. Sand and water iii. Alcohol and water iv. Sugar and water c. The mixture of sand and water can be separated by..... i. Filtration ii. Winnowing iii. Sieving iv. Magnetic separation d. The mixture of iron fillings and sand can be separated by....... i. Sedimentation ii. Magnetic separation iii. Sieving iv. Filtration e. The method of separating rice husks from rice is called ........ i. Filtration ii. Sieving iii. Winnowing iv. Decantation 4. Match the following. a. Salt solution i. filtration b. Funnel ii. homogeneous mixture c. Winnowing iii. wind is needed d. Magnet iv. heterogeneous mixture e. Flour and water v. separates magnetic substances STEP2 5. Answer the following questions in one word. a. Which method is used to separate tea leaves from tea? b. What kind of mixture is muddy water? c. What is the term used for ‘the method of separating the mixture of solid particles of different sizes by using a sieve’? d. What is the term for clear liquid collected in a beaker after filtration?

174 Modern Concept Science and Technology Book 5 e. How many types of mixtures are there on the basis of distribution of components? 6. Write any two differences between: a. Homogeneous mixture and heterogeneous mixture b. Sieving and filtration c. Sieve and filter paper d. Filtration and sedimentation 7. Give reasons. a. Sugar solution is called a homogeneous mixture. b. Salt and water cannot be separated by filtration. c. Magnet is used to separate magnetic substances. d. Filter is used in our kitchen for drinking water. 8. Write down the name of the following method of separating mixtures and mention one use of each. a. b. c. d. e. f.

Modern Concept Science and Technology Book 5 175 STEP3 9. Answer the following questions. a. Define the mixture with any three examples. b. How many types of mixtures are there? Write their names. c. What is a homogeneous mixture? Write any two examples. d. What is heterogeneous mixture? Write any two examples. e. Write any four importance of mixtures. f. What are the components of a mixture? Explain with the examples. g. Define filtration with a diagram. h. What is sedimentation and decantation? Draw its diagram. i. What are magnetic substances? Write any two examples. 10. Identify the method of separating the following mixture. a. Sand and iron filing b. Tea leaves and tea c. Rice husks and rice d. Sand and water

176 Modern Concept Science and Technology Book 5 Unit 7 Energy

Modern Concept Science and Technology Book 5 177 Key terms and terminologies of the unit 1. Light: Light is a formof energy which causes a sensation of vision in our eyes. 2. Source of light: The objects which produce the light are called of sources light. 3. Natural sources of light: The bodies which emit the light naturally are called natural sources of light. 4. Artificial sources of light: The man-made bodies which emit the light are called artificial sources of light. 5. Luminous bodies: The bodies which are able to emit the light themselves are called luminous bodies. 6. Non-luminous bodies: The bodies which are unable to emit the light themselves are called non-luminous bodies. 7. Transparent bodies: The bodies which allow the light to pass through them are called transparent bodies. 8. Translucent bodies: The bodies which allow a part of light to pass through them are called translucent bodies. 9. Opaque bodies: The bodies which do not allow the light to pass through them are called opaque bodies. 10. Propagation of light: The transmission of light from one place to another place is called propagation of light. Sequence of Curriculum Issued by CDC  Sources of light  Luminous and non-luminous bodies  Transparent, translucent and opaque objects  Colours of light UNIT Light 7.1 Estimated teaching periods Theory Practical 6 2 Antonie van Leeuwenhoek is a Dutch microscopist. He was born in1632 and died in 1723 in The Netherlands. He invented simple microscope capable of studying micro-organisms, mainly large bacteria and protozoans. His observations helped lay the foundations for the sciences of bacteriology and protozoology. For his honour, he is popularly known as the father of microscope. Antonie van Leeuwenhoek About the Scientist

178 Modern Concept Science and Technology Book 5 11. Rectilinear propagation of light: Propagation of light in a straight path through a transparent homogeneous medium is called rectilinear propagation of light. 12. Ray of light: A very narrow path of light is called a ray of light. 13. Beam of light: A collection of many rays of light is called a beam of light. 14. Shadow: The dark space formed behind an opaque object when it is kept in the path of light is called shadow. 15. Pinhole camera: The simple camera which has a small hole without a lens is called pinhole camera. Introduction We see various things around us during day but we cannot see things in a dark room in night. You might have observed that all the things in your room disappear and only a dark black colour is seen when you turn off light in your room in night. Only our eyes are not responsible to see the things around us but light also is equally important to see the things. Objects are invisible in a dark room in night even though we keep our eyes open because there is no light. Thus, light must be there to see things around us. Light is a form of energy which causes a sensation of vision in our eyes. Light is necessary for humans and other animals to see things. Plants can prepare their own food in presence of the sun light. Sources of light The objects which produce light are called sources of light. For example, the sun, glowing bulb, burning candle, lantern, torch light, firefly, etc. These sources emit light and make things visible. There are different sources of light. They are mainly divided into two categories. They are: a. Natural sources of light b. Artificial sources of light a. Natural sources of light The bodies which emit the light naturally are called natural sources of light. For example: the sun, moon, stars, firefly, etc. i. Sun The sun is the major natural source of light on the earth. The sun is one of the countless stars in the sky. All the stars produce In the sun there occurs thermonuclear fusion, so it produces heat and light continuously. MEMORY TIPS Sun

Modern Concept Science and Technology Book 5 179 light and spread to the objects around them. During the day, the sun rises and light comes to the earth. We can see things easily in daytime due to the sunlight. Plants make their food and give oxygen by using the sunlight. There is no other object on the earth which gives light as much as the sun does. Therefore, the sun is called the major source of light on the earth. FACTS WITH REASONS Why is the sun called major natural source of light on the earth? There is no other object on the earth which gives light as much as the sun does. Therefore, the sun is called the major source of light on the earth. ii. Moon The moon is a natural satellite of the earth. With the moon in the sky, the night also becomes little bit brighter. The moon reflects light coming from the sun towards the earth. So, it appears brighter. Actually the moon does not produce light on its own. It is like a mirror reflecting the sunlight. The light coming from the moon is not sufficient to read and write. However, we can walk easily in the moonlight. iii. Stars The stars appear twinkling during the night. Even though the stars are very big and brighter, they give almost no light to the earth because they are very far away from the earth. iv. Firefly (Junkiri) Fireflies emit light from their tails. The light emitted from the fireflies is insufficient to see the things. b. Artificial sources of light The man-made bodies which emit the light are called artificial sources of light. For example, lamps like kerosene lamp, burning candle, lantern, torch light, etc. Moon The moon gives maximum light on the full moon day and does not give light on the new moon day. MEMORY TIPS Firefly Lamp

180 Modern Concept Science and Technology Book 5 i. Lamp Lamps like kerosene lamp, candle, lantern, etc. are some examples of artificial sources of light. These sources need fuels like kerosene, wax, etc. On burning fuels, they produce light along with heat. ii. Electricity Electricity is a form of energy. It can be converted into light energy using electric bulbs, fluorescent lamp, CFL, LED bulb, etc. Electric bulbs are used in houses, roads and other places to produce light. These days, electricity is an important source of light in the houses. ACTIVITY 1 OBJECTIVE : To list different sources of light Make a list of any 10 different sources of light which are present around you. What do they use to produce light? You can make a similar type of table to write them. S.N. Sources of light What do they use to produce light? 1. Bulb Electricity Luminous and Non-luminous Bodies There are two types of bodies. Some bodies are able to emit light themselves like the sun, the stars, electric bulb, etc. Similarly there are some other bodies like stone, book, table, chair, glass, etc. which are unable to emit light themselves. So, on the basis of emission of light, there are two types of bodies. They are: a. Luminous bodies b. Non-luminous bodies a. Luminous bodies The bodies which are able to emit the light themselves are called luminous bodies. The sun, the stars, lamp, electric bulb, fluorescent bulb, burning candle, etc. emit light themselves. So, they are called luminous bodies. Luminous bodies are bright and shiny. They make other things visible. Electric bulb CFL = Compact Fluorescent Lamp, LED = Light Emitting Diode MEMORY TIPS

Modern Concept Science and Technology Book 5 181 Differences between luminous bodies and non-luminous bodies S.N. Luminous bodies S.N. Non-luminous bodies 1. The bodies which are able to emit the light themselves are called luminous bodies. 1. The bodies which are unable to emit the light themselves are called nonluminous bodies 2. Luminous bodies are always visible. Example: sun 2. Non-luminous bodies are visible only if it reflects light. Example: moon ACTIVITY 2 OBJECTIVE : To list luminous bodies Make a list of 10 luminous bodies around you. Mention whether they are natural or man-made. You can use a similar type of table to list them. S.N. Luminous bodies Natural or man–made 1. Sun Natural b. Non-luminous bodies The bodies which are unable to emit the light themselves are called non-luminous bodies. For example, stone, soil, table, chair, glass, water, tracing paper, air, book, pen, pencil, moon, earth, planets, etc. They become visible only in the presence of other sources of light. Non-luminous bodies are of three types. They are transparent bodies, translucent bodies and opaque bodies. i. Transparent bodies The bodies which allow the light to pass through them are called transparent bodies. Glass, air, atmosphere, clean water, etc. are some examples of transparent bodies. Transparent bodies absorb and reflect a little part of light which fall The moon is a non-luminous body because it cannot emit light itself. It reflects the sunlight and becomes visible. MEMORY TIPS Transparent objects do not form a shadow, translucent objects form a faint shadow and opaque objects form a dark shadow. MEMORY TIPS

182 Modern Concept Science and Technology Book 5 upon them and allow most of the light to go through them. The colour of a transparent body depends on the colour of the light it transmits. FACTS WITH REASONS Glass cannot cast shadow, why? Glass cannot cast shadow because it is a transparent object and does not block light at all. ii. Translucent bodies The bodies which allow a part of light to pass through them are called translucent bodies. Tracing paper, white paper immersed in oil, wax paper, ground glass, etc. are some examples of translucent bodies. Translucent bodies absorb and reflect most of the light which fall on them. iii. Opaque bodies The bodies which do not allow light to pass through them are called opaque bodies. Stone, book, pen, pencil,brick, chair, table, wall, etc. are some examples of the opaque bodies. When opaque bodies block light, shadow falls behind. The opaque bodies either absorb or reflect light. But they do not allow light to pass through them. FACTS WITH REASONS Why is brick called an opaque object? Brick is called an opaque object because it does not allow the light to pass through and blocks 100% light. ACTIVITY 3 OBJECTIVE : To distinguish transparent, translucent and opaque objects. Take a survey around you, your home and your school. Make a list of 20 objects which are available there. Then, divide them in the group of transparent, translucent and opaque objects. Make a similar type of table to fill them. Transparent objects Translucent objects Opaque objects 1. Window glass 1. Tracing paper 1. Brick A white paper is an opaque body but it becomes translucent when it is immersed in oil. MEMORY TIPS

Modern Concept Science and Technology Book 5 183 Colour of light Have you seen rainbow in the sky? Do you know when does we see it? Can you name the colours in the rainbow? Of course, we see rainbow after rainfall or when the air has water droplets in it. Rainbow forms when the water droplets scatter the sunlight. It means the colour we see in the rainbow is the colour of the light. The light is made up of seven different colours. They are violet, indigo, blue, green, yellow, orange and red. When we rotate a disk coated with different colours of sunlight in equal portion in high speed, the coloured disk looks white. It means we can conclude that the sunlight is white in colour. Look below in the figure, how glass prism scatters sunlight into different colour bands. Look which colour is at the top of the band and which is at the bottom. Fig: Glass prism scattering light Fig: Disc coloured with all 7 colours of light Propagation of Light Light travels from one place to another place in the form of a wave. Its speed is very high. It is about three hundred thousands kilometre in one second. So, the transmission of light from one place to another place is called propagation of light. It always travels in a straight line unless other substances or medium come in its way. This is called rectilinear propagation In one medium light also does not travel in a straight path if density of the medium goes on changing. MEMORY TIPS Fig: Rainbow

184 Modern Concept Science and Technology Book 5 of light. Thus, the propagation of light in a straight path through a transparent homogeneous medium is called rectilinear propagation of light. Light passing through a straight pipe Light doesn’t pass through a curved pipe FACTS WITH REASONS We cannot see beyond a wall, why? Light always travels in a straight line and the opaque wall blocks it completely. So, we cannot see beyond the opaque wall. ACTIVITY 4 Objective : To show the rectilinear propagation of light. Requirement : Three cardboards of equal size, candle, matchbox, stand, etc. Methods : Take three equal sized cardboards and make a hole in each of them. Stand the cardboards vertically so that all the holes lie in a straight line. Lit a candle and put at one side and observe from other side. Now, slightly change the position of the central cardboard and observe again. What do you observe? Observation : When all the holes of cardboards are in a straight line, we can see the flame of the candle. After changing the position of the central cardboard the holes do not lie in a straight line. So we cannot see the flame of the candle. Conclusion : From the above activity, it is clear that light always propagates in a straight line. Ray and beam of light A very narrow path of light is called a ray of light. It is a single wave of light. It is represented by a straight line with an arrowhead. An arrowhead drawn upon the ray of light indicates the direction of propagation of light. A ray of light is almost invisible to our eyes. The collection of many rays of light is called a beam of light. A beam of

Modern Concept Science and Technology Book 5 185 light can be produced when light is passed through a pin hole. Actually what we see in the source of light is a beam, it is not a ray. The beam of light may be parallel, divergent or convergent. Parallel beam Divergent beam Convergent beam Differences between ray of light and beam of light S.N. Ray of light S.N. Beam of light 1. A very narrow path of light is called ray of light. 1. Collection of many rays of light is called beam of light. 2. A ray of light is represented by a straight line with an arrowhead. 2. A beam of light is represented by two or more parallel rays with arrow heads. Shadow Light always travels in a straight line. When the path of light is blocked by an opaque object, we can see the dark picture of the blocking object at its back. This dark space is called a shadow. Thus, the dark space formed behind an opaque object when it is kept in the path of light is called shadow. HOT SKILL HIGHER ORDER THINKING SKILL 1. Define light energy. Give any two examples of natural sources of light. Light is a form of energy which causes a sensation of vision in our eyes. Two natural sources of light are: sun and stars. 2. Give any four examples of artificial sources of light. Four artificial sources of light are: i. Kerosene lamp ii. Bulb iii. Table lamp iv. Torch light 3. What are luminous bodies? Give any two examples. The bodies which are able to emit light themselves are called luminous bodies. Examples: Sun, glowing bulb. Shadow

186 Modern Concept Science and Technology Book 5 4. Differentiate between transparent objects and opaque objects with examples. Differences between transparent objects and opaque objects are: S.N. Transparent objects S.N. Opaque objects 1 The bodies which allow light to pass through them are called transparent objects. 1 The bodies which do not allow light to pass through them are called opaque objects. 2 Transparent objects do not make a shadow. 2 Opaque objects make a shadow. 5. What is the term used for objects which partially blocks light? The term used for the objects which blocks light partially is called a translucent object. 6. What is a shadow? How is it formed? The dark space formed behind an opaque object when it is kept in the path of light is called a shadow. Shadow is formed when the light is blocked by any object. 33 STEPS STEPS EXERCISE EXERCISE STEP1 1. Fill in the blanks with appropriate words. a. Light causes a sensation of _________________ . b. The objects which __________ light are called opaque. c. A __________ object can produce light of its own. d. Light travels in __________path. e. Electric bulbs are __________ of light. 2. Write True for the correct and False for the incorrect statements. a. The sun is the major source of light on earth. b. The earth is a luminous object. c. Water is an opaque body. d. The collection of beam of light is called a ray of light. e. Light travels in a straight path.

Modern Concept Science and Technology Book 5 187 3. Select the best answer from the given alternatives. a. Light is a form of: i. force ii. power iii. energy iv. speed b. Which one is a non-luminous body? i. moon ii. stars iii. fire fly iv. candle c. Which one among these is a transparent medium? i. tracing paper ii. water iii. wall iv. atmosphere d. The sun is a source of light because: i. It is far away ii. It is hot iii. It produces light iv. It sets during the night 4. Match the following. a. The sun i. Tracing paper b. Moon ii. Luminous object c. Transparent iii. Book d. Translucent iv. Non-luminous object e. Opaque v. Glass STEP2 5. Answer the following questions in one word. a. Give one example of an artificial source of light energy. b. What type of source of light is the sun? c. Is the moon a luminous object? d. What kind of objects cannot cast the shadow? e. What is the term used for a dark spot formed when the light is blocked? 6. Give reasons. a. The sun is called the major natural source of light on the earth. b. A brick is called an opaque object. c. The moon is not a luminous object. d. Glass cannot cast a shadow. e. We cannot see beyond an opaque wall.

188 Modern Concept Science and Technology Book 5 7. Write down the name of following objects and mention one use of each. a. b. c. translucent screen light shield pinhole black paper d. e. f. STEP3 8. Answer the following questions. a. Define light energy. b. What do you mean by a source of light? Give two examples. c. Define luminous object and non-luminous object with an example of each. d. What is ray of light? Show in a diagram. e. Define beam of light and show in a diagram. f. Give any four examples each of the artificial sources of light and natural sources of light. g. How does a shadow form? Write in short. h. Define rectilinear propagation of light with the help of a diagram. i. What is a transparent object? Give any two examples. j. Define translucent object and opaque object with an example of each. k. When does rainbow occur in the sky? Illustrate the conditions for rainbow formation. 9. Identify luminous and non-luminous objects: a. star b. moon c. earth d. candle e. electric bulb f. mirror

Modern Concept Science and Technology Book 5 189 Key terms and terminologies of the unit 1. Sound: Sound is a form of energy which produces a sensation of hearing in the ears. 2. Sources of sound: The vibrating bodies which produce sound are called sources of sound. 3. Musical sound: The sound which has a pleasing effect on our ears and mind is called a musical sound. 4. Noise: The sound which has unpleasing effect on our ears and mind is called noise. 5. Pitch: The shrillness of a sound is called the pitch. 6. Loudness: Loudness is a characteristics of sound by which a loud sound can be distinguished from a faint sound. 7. Waves: Wave is a path of energy which is produced due to the disturbance in a medium. 8. Transverse wave: The waves in which vibration of the medium particles and the direction of the wave propagation are perpendicular to each other are called transverse waves. Sequence of Curriculum Issued by CDC  Introduction to sound  Sources of sound  Musical sound and noise, and conditions in which they are produced  Shrillness and loudness of sound, and conditions in which they are produced  Effects of noise and our activities to reduce noise UNIT Sound 7.2 Estimated teaching periods Theory Practical 6 2 Alexander Graham Bell was a Scottish-born American inventor, scientist, and teacher of the deaf. He was born in 1847 in Scotland and died in 1922, in Canada. His important accomplishments were the invention of the telephone in 1876 and the refinement of the phonograph (record player) in 1886. Alexander Graham Bell About the Scientist

190 Modern Concept Science and Technology Book 5 9. Longitudinal waves: The waves in which vibration of the medium particles and the direction of the wave propagation are parallel to each other are called longitudinal waves. 10. Propagation of sound waves: The transmission of sound waves from one place to another is called propagation of sound waves. Introduction We hear different types of sounds every day. The blowing horn, sound of school bell, lecture of teachers, speech of a leader, barking of a dog, chirping of birds, sound of vehicles, music in radio, TV, etc. are some common examples of sound we hear every day. Sounds produce a sensation of hearing in our ears. So, sound is a form of energy which produces a sensation of hearing in the ears. All kinds of sounds are produced due to vibration of the substances. When we speak, our throat vibrates which produces a sound. We hear a sound by our ears. Sources of Sounds The vibrating bodies which produce sound are called sources of sound. Musical instruments like sarangi, madal, guitar, drum set, the horn of a vehicle, whistle, barking dog, radio, cassette player, television, temple bell, etc. are some examples of sources of sound. In the sources of sound, the whole body or a part of the body vibrates to produce the sound. When you play a radio, its speaker vibrates to produce the sound. Similarly, string in sarangi vibrates to produce the sound. Different sources of sound produce different kinds of sound. So, we can identify objects even by their sound. We can easily distinguish a dog’s barking from the sound of the bird’s chirping even without seeing them. Bell Madal Tuning fork Whistle Fig: Sources of sound We cannot hear all kinds of sounds. For example, infrasound and ultrasound. MEMORY TIPS

Modern Concept Science and Technology Book 5 191 FACTS WITH REASONS Why do different people have different voices? Different people have different voices because of a difference in the size of their vocal cord. ACTIVITY 1 Objective : To observe the vibration in a source of sound. Requirement : A madal, some wheat flour Methods : 1. Take a madal and keep it vertically as shown in figure. 2. Hit its upper skin and put some wheat flour immediately. You will see flour vibrating until you hear sound of the madal. The vibration of flour will cease as soon as the sound stops. Conclusion : This activity proves that the vibration in an object produces sound. Types of Sound We hear different types of sounds every day. Some of the sounds like song, music, etc. have a pleasant effect while the sound of quarreling people is very disturbing to our mind. So, on the basis of effect of sound upon us, we can divide sounds into two groups. They are: a. Musical sound b. Noise a. Musical sound We feel very comfortable and relaxed when we hear a melody music. The sound which has pleasing effect to our ears and mind is called a musical sound. It is harmonious and tolerable. For example, sound of songs, birds and sound of musical instruments like guitar, piano, flute, madal, violin, etc. Flute Guitar Madal Fig: Sources of musical sound Tuning fork is a U-shaped metal piece with a stem. It is used in the laboratory to perform laboratory activities of sound. MEMORY TIPS

192 Modern Concept Science and Technology Book 5 b. Noise The blow of horn, barking dog, random shouting of people, thunderstorm, sound of industry and factory, etc. are very irritating. We do not want to hear these kinds of sounds. They are called noise. Thus, the sound which has an unpleasing effect to our ears and mind is called noise. It should be noted that the musical sound to someone can be a noise to others. For example, when you listen fast and rap songs your grandmother could say that what a quarreling sound it is. Differences between music and noise S.N. Music S.N. Noise 1 The sound which has a pleasing effect to our ears and mind is called a musical sound. 1 The sound which has an unpleasing effect to our ears and mind is called noise. 2 Music is a harmonious and tolerable sound. 2 Noise is a non-harmonious and intolerable sound. ACTIVITY 2 OBJECTIVE : To distinguish a musical sound and noise. Identify the different sources of sound around you and list in the following table. Also classify sounds produced by them into musical sound and noise. S.N. Sources of sound Musical sound or noise 1. Radio Musical sound Characteristics of Musical Sound The pleasant sound has mainly two characteristics. They are: a. Pitch b. Loudness a. Pitch The voice of children and girls is shriller than the voice of adults and boys. So, the shrillness of a sound is called the pitch. The pitch of sound cannot be measured but it can be felt. We can distinguish shrill sound and hoarse sound with the help of The number of vibrations produced per second is called a frequency. MEMORY TIPS Loudness and sharpness of a sound are different things. For example, the sound produced by a buffalo is loud but not sharp. Similarly, the sound produced by mosquito wings is sharp but not loud. MEMORY TIPS

Modern Concept Science and Technology Book 5 193 its pitch. The sound with high frequency of the vibration has high pitch and the sound with low frequency of the vibration has low pitch. ACTIVITY 3 Objective : To show that the sharpness of a sound is more if there is high frequency Requirement : Rubber band and knife Methods : 1. Take a rubber band and fix its one end at a rigid support and stretch it from the other end with your hand. Pluck the rubber band with another hand. Listen the sound produced. 2. Stretch the rubber band more and pluck it again. 3. Now, cut the rubber band into two halves. Take one piece and repeat the same process again. Observation : In the first case the sound is dull and in the second case the sound is sharp. In the third case the sound heard is sharper than that from the first and second case. Conclusion : The above activity shows that, the stretched rubber has high frequency and produces a sharp sound. Similarly, the sound from a short rubber band has high frequency than that from the long one. So, it produces sharper sound. FACTS WITH REASONS Why is the sound of a girl sharper than that of an adult man? Sound of a girl is sharper than that of an adult man because girl’s vocal cord is smaller than the vocal cord of an adult man. Which produces high frequency sound with high pitch. b. Loudness The sound produced by a big bell is louder than the sound by a small bell. Similarly, the sound produced by a thick string of a guitar is louder than that from the thin string. So, loudness of a sound depends upon the size of the vibrating body and the degree of vibrations. The sound produced by a big body carries more energy than the sound produced by a small body. Likewise, a louder sound propagates up to a longer distance than the faint sound. Therefore, loudness is a characteristics of a sound by which a loud sound can be distinguished from a faint sound. Loudness of a sound increases with the force of vibration. When vibrating molecule is displaced more, there is increase in the loudness of the sound.

194 Modern Concept Science and Technology Book 5 Beating of a drum, explosions etc. produce loud sounds. Big animals have a big sized sound producing organ. So, the sound produced by them is louder and can be heard over a long distance. Similarly, small animals have a small sound producing organ and it produces a sharp sound. Sharp sounds cannot be heard over a long distance. FACTS WITH REASONS Sound of the big bell in a temple is louder and can be heard at a long distance than that from the bell hanged in dog’s neck. Why? Loudness of a sound depends upon size of the source of sound. Temple bells are bigger than the bell in dog's neck. So the temple bells produce a louder sound that travels farther. ACTIVITY 4 Objective : To show that loudness of sound depends upon the degree of vibration. Requirement : A guitar and a piece of paper Method : Make a small ring of paper and adjust it in the guitar’s string. Pluck the string of guitar softly and observe the paper. Now, pluck the string of guitar hardly and observe the paper again. Observation : When the string is plucked softly, a soft sound is heard and the paper vibrates slowly. But when the string is plucked hardly, a loud sound is heard and the paper vibrates violently. Conclusion : The above activity shows that the loudness of sound increases with the increase in vibration of the body. Introduction to Wave Motion Take a piece of stone and throw it into a pond. It produces ripples on the water surface. Similarly, take a soft spring and compress it in between your hands vertically. Now, release the spring from the lower hand and observe the motion. The spring moves up and down continuously for some time. The ripples in the pond and up-down motion of the spring are called waves. Therefore, a wave is the path of energy which is produced due to the disturbance in a medium. In wave motion, the medium particles do not move from one place to another. They just vibrate up and down or to and fro and transfer energy to the nearby molecules. For example, when we drop a piece of stone into a pond, the water molecules near the stone get energy from the stone and start to vibrate up and down. These vibrating water molecules transfer

Modern Concept Science and Technology Book 5 195 energy to the nearby water molecules. The process of transferring energy continues to the water molecules of the edge. Thus, in wave motion, there occurs transfer of energy but does not occur transfer of medium particles. There are two types of waves. They are: a. Transverse waves b. Longitudinal waves a. Transverse waves The waves in which vibration of the medium particles and the direction of the wave propagation are perpendicular to each other are called transverse waves. For example, waves in water, waves in string, etc. Transverse waves move by making crest and trough. b. Longitudinal waves The waves in which vibration of the medium particles and the direction of the wave propagation are parallel to each other are called longitudinal waves. For example, sound waves, waves in a spring, etc. Longitudinal waves move by making compression and rarefaction. Differences between transverse wave and longitudinal wave: S.N. Transverse wave S.N. Longitudinal wave 1 The waves in which vibration of the medium particles and the direction of the wave propagation are perpendicular to each other are called transverse waves. 1 The waves in which vibration of the medium particles and the direction of the wave propagation are parallel to each other are called longitudinal waves. 2 Transverse waves move by making crest and trough. Example: light wave 2 Longitudinal waves move by making compression and rarefaction. Example: sound wave The circular waves in water which move towards the edge are called ripples. MEMORY TIPS Fig: Transverse wave (a wave in water) The phenomenon by which sound travels from one place to another place is called transmission of sound. MEMORY TIPS

196 Modern Concept Science and Technology Book 5 ACTIVITY 5 1. Visit a nearby pond and drop a piece of stone into water at center of the pond. 2. Observe the surface of water. Do ripples produce on the surface of water? 3. Let the water be calm and drop a big stone in this case. 4. Observe and compare the ripples produced before and now. 5. Now, throw a piece of paper or a leaf on the surface of water and observe its motion. 6. Write down the conclusion of this activity in your exercise book. Propagation of sound wave Sound waves are the longitudinal waves. They move from one point to another by making compression and rarefaction of the medium particles. Thus, the transmission of sound waves from one place to another place is called propagation of sound waves. The sound waves produced by a vibrating body propagate in air and reach to our ears. This causes a sensation of hearing to our ears. Sound waves are also called mechanical waves because they need a material medium to propagate. Thus, sound can propagate through solids, liquids and gases. But it cannot propagate through vacuum. FACTS WITH REASONS Sound is heard on the earth but it cannot be heard in space, why? Earth has air around it, which transfers sound from one place to another. But sound cannot be heard in space because there is no air to transfer sound. We know that air is a mixture of various gases, so sound can propagate through air. The speed of sound in air is about 332 m/s. Sound cannot propagate on the moon surface because there is no air. This is a reason why astronauts use special electronic devices to communicate on the surface of the moon. Sound can also propagate through a liquid medium. In water the speed of sound is about 1498m/s. Similarly, sound can propagate through solid medium. The speed of sound in solid is more than that in liquid and gas. The speed of sound is maximum in solids and minimum in gases. In liquids, speed of sound is more than that in gases but less than that in solids. MEMORY TIPS

Modern Concept Science and Technology Book 5 197 Thread Hi ! Hello ! Bell Bucket Hammer Water Propagation of sound in solid Propagation of sound in liquid Fig: Propagation of sound ACTIVITY 6 Objective To demonstrate that sound propagates through a solid. 1. Keep your head on a desk resting one ear on its side. 2. Ask to your friend to put a watch at the other end. 3. What do you feel? The sound is loud and heard very fast. 4. Now, remove your ear from the desk and again ask your friend to put a watch on the desk and listen the sound. 5. Compare the sounds you heard before and now. 6. Share your result with your teacher and friends. ACTIVITY 7 Objective : To demonstrate that sound propagates through a liquid medium. 1. Take a bucket full of water. 2. Take a bell and a hammer and dip them into the bucket. 3. Strike the bell inside water in the bucket. 4. Do you hear the sound outside? Yes. 5. This activity proves that sound can propagate through a liquid medium. Bell Bucket Hammer Water Effects of Noise and Measures to Reduce It Do you like to study in noisy environment? Of course not. In humans, noise cause loss to attention, anger and anxiety. Increase in blood pressure and headache are some common problems of noise. Loud noise of short-term result temporary hearing loss while long term exposure to large volume of sound causes deafness. Noise affects not only human beings but other

198 Modern Concept Science and Technology Book 5 organisms also. Noise forces wild creatures to leave their habitat and to search for new. It takes away the peace and calmness of places and minds. Measures to reduce noise There are a number of ways to reduce the effects from the noise. To reduce and control the effects from noise, some measures that we can follow are listed below. 1. Making the habit of speaking in soft and low volume. 2. Listening music and watching movies in small volume. 3. Using earplugs or headphones for listening music personally. 4. Avoiding unnecessary chatting in the class. 5. Planting trees and vegetations around the house as they absorb sound. 6. Avoiding conversation in high volume in public spaces like hospitals, buses, planes, schools, restaurants etc. 7. Keeping ourselves away from the noisy environment. HOT SKILL HIGHER ORDER THINKING SKILL 1. Define sound energy. Write the name of any four sources of sound energy. Sound is a form of energy which produces a sensation of hearing to the ears. Four sources of sound energy are: bell, running engine, clapping, loud speaker 2. What is a musical sound? Give any two examples. The sound which has a pleasing effect to our ears and mind is called a musical sound. Examples: chirping of birds, song, etc. 3. What is a wave? List out the types of waves on the basis of vibration of particles. A wave is the path of energy which is produced due to the disturbance in a medium. There are two types of waves. They are: i) Longitudinal wave and ii) Transverse wave 4. What is a longitudinal wave? Give two examples. The waves in which vibration of the medium particles and the direction of the wave propagation are parallel to each other are called longitudinal waves. Example: Sound wave, waves in springs. 5. Differentiate between light and sound. Differences between light and sound are: SN. Light SN. Sound 1. Light is the form of energy which produces a sensation of vision in the eyes. 1. Sound is a form of energy which produces a sensation of hearing to the ears. 2. Light is a transverse wave. 2. Sound is a longitudinal wave.

Modern Concept Science and Technology Book 5 199 6. Draw a diagram to show a transverse wave. 7. Which type of wave is the sound wave? Sound wave is a longitudinal wave. 8. What is the value of speed of sound in water and air? The speed of sound in water is 1498 m/s and in air is 332 m/s. 33 STEPS STEPS EXERCISE EXERCISE STEP1 1. Fill in the blanks with appropriate words. a. Sound is due to _______________of sounding body. b. Sound travels in a medium as a ______________wave. c. _________is the sound which has an unpleasing effect to our ear. d. Pitch of a sound depends on______________ . e. Chirping of bird is considered as a ______________ sound. 2. Write True for the correct and False for the incorrect statements. a. Sound is produced due to heating of a medium. b. Sound is a longitudinal wave. c. Speed of sound is greater in water than in air. d. Melodious sound of a flute is noise. e. Different people have different sounds.

200 Modern Concept Science and Technology Book 5 3. Select the best answer from the given alternatives. a. A vibrating body produces: i. sound ii. light iii. electricity iv. none of the above b. Song is a …….. sound. i. musical ii. noisy iii. melodious iv. sweet c. Sound wave is ………… of particles of medium. i. continuous flow ii. to and fro motion iii. random motion iv. dancing motion d. Speed of sound in air is …………m/s. i. 332 ii. 33.2 iii. 3.32 iv. 3320 e. Velocity of sound is maximum in a...... medium. i. solid ii. liquid iii. gas iv. fluid 4. Match the following. a. Sound i. Noise b. Light ii. Music c. Guitar iii. Transverse wave d. Rally iv. Longitudinal wave e. Wave v. A path of energy STEP2 5. Answer the following questions in one word. a. What is the term used for a sound that produces a pleasant effect to our ear?