Oasis School Science and Technology -5 147 3. Tick ( √ ) the true statements and cross (x) the false ones. a. Matter does not occupy space. ( ) b. Volume is the total space occupied by a body. ( ) c. Water is a solid substance. ( ) d. Gases have a fixed shape and size. ( ) e) Liquids are hard and rigid. ( ) f. In solids, molecules are loosely held. ( ) g. Water vapour is a gas. ( ) 4. Match the following: A B • Solid Form a matter • Liquid Can spread everywhere • Gas Hard and rigid • Water vapour Flows from one place to another • Molecules No fixed shape and volume Gaseous form of water 5. Give very short answer to the following questions. a. What is matter made up of ? b. Which state of matter has fixed shape and volume? c. Which state of matter has fixed volume but takes the place of vessel it is kept? d. Which state of matter has neither fixed shape nor fixed volume? 6. Give reasons: a. Wood and stone are called solids. b. Gas does not have a fixed shape and volume. c. Water and milk are called liquids. d. Solids have a fixed shape and volume.
148 Oasis School Science and Technology -5 7. Differentiate between: a. Solid and Liquid b. Liquid and Gas c. Solid and Gas 8 Give short answers to the following questions. a. What is matter? Name three states of matter? b. What is volume? c. Write any two properties of matter. d. Name any two heavy and two light substances. e. What are solids? Give any three examples. f. What are liquids? Give any three examples. g. What are gases? Give any two examples. h. Write any two properties each of solid, liquid and gas. 9. Name any three solids, three liquids and two gases which are used in our daily life. 10. What conclusion can be drawn from the following figures? Write. 11. Classify the following substances into solid, liquid and gas. stone air book ink milk juice cocacola diesel pen ice oxygen wood table desk plastic paper rock oil
Oasis School Science and Technology -5 149 Key terms and terminologies 1. Heat : Heat is a form of energy which gives the sensation of warmth or coldness. 2. Sources of Heat : The object from which heat can be obtained is called the source of heat. 3. Bio-Fuel : The fuel obtained from firewood, bio-gas, straw, dried cow-dung, etc. is called bio-fuel. 4. Fossil Fuel : The fuel obtained from fossils is called fossil fuel. 5. Expansion : Process of increase in the volume of solid, liquid and gas on heating is called thermal expansion UNIT 6.2 EFFECTS OF HEAT ON MATTER Estimated teaching periods Theory 8 Practical 2 Effects of heat in state and volume of matter Advantages and disadvantages of effects of heat The Sequence of Curriculum Issued by CDC James Prescott Joule was an English physicist. He was born 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 honored after his name. About the Scientist James Prescott Joule
150 Oasis School Science and Technology -5 Introduction When we touch a piece of burning coal, we feel hot. When we stand in the sun or sit near a fire, we feel hot. Similarly, if we touch a piece of ice, we feel cold. A body becomes hot due to the presence of a form of energy known as heat energy. When heat flows into our body from a hot body, we get the sensation of warmth. When heat flows out of our body, we get the sensation of coldness. So, heat is a form of energy which gives the sensation of warmth or coldness. Heat is measured in joule (J), calorie (cal.), etc. In our daily life, we use heat for various purposes like cooking food, drying clothes, heating water, getting warm, running engine, etc. Heat is an important form of energy for living beings. Animals and plants cannot survive in very cold environment. Many plants get dried in cold season and many animals go for hibernation during winter. In our country, some people die due to excessive cold during the winter season. Similarly, we feel uneasy in very hot environment. So, the presence of too hot or too cold environment is not good for living beings. Heat is a form of energy which can be transformed into other forms of energy. Similarly, other forms of energy can also be transformed into heat energy. Sources of Heat The object from which heat can be obtained is called the source of heat. The major sources of heat energy are given below: i. Sun ii. Bio-fuel iiii. Fossil fuel iv. Electricity i. Sun The sun is the major source of heat energy. Living beings cannot survive in the absence of solar heat. We feel cold during winter as we get less heat Fig: Sunbathing
Oasis School Science and Technology -5 151 from the sun. Similarly, we feel cold if the weather is cloudy as we get less heat from the sun. Animals and plants get heat energy from the sun. The water cycle operates on the earth due to the heat of the sun. Now-a-days, solar heat is used to make solar cooker, solar water heater and solar battery. ii. Bio-fuel The fuel obtained from firewood, bio-gas, straw, dried cow-dung, etc. is called bio-fuel. We get heat energy by burning bio-fuel. In rural areas, bio-fuel is the main source of heat energy. People use bio-fuel for cooking food, making rooms warm, boiling water, etc. In rural areas, people dry the dung of cattle to make cakes which are used as a source of heat for cooking food. Similarly, people use animal dung for making biogas or gobar gas. It is used for cooking food and lighting rooms. Fig: Bio-fuel producing heat iii. Fossil fuel The fuel obtained from fossils is called fossil fuel. Fossils are the remain of plants and animals that are buried in the earth million of years ago. Petrol, diesel, kerosene, Fig: Fossil Fuels producing heat
152 Oasis School Science and Technology -5 natural gas, air turbine fuels, coal etc. are examples of fossil fuels. Fossil fuels are extracted from deep below the earth surface. Kerosene and natural gas (LP gas) are used for cooking food and making room warm. Fuels like petrol, diesel, etc. are used for running the engines of motorcycle, truck, bus, aeroplane, etc. The fuel used in engines also produces heat energy. Coal is also used for getting heat energy. Therefore, fossil fuel is also a main source of heat energy. We face energy crisis in the absence of fossil fuel. iv. Electricity We can also get heat energy from electricity. Electric heater is used to convert electrical energy into heat energy. In urban areas, people use electricity to cook food and to get heat. Nepal is rich in running water resources. So, we can produce hydroelectricity in a large scale. It can be used for getting heat and light. Similarly, hydroelectricity can be used in industries for various purposes. Therefore, electricity is also a main source of heat energy. It is a pollution-free source of heat energy. Fig: Electricity producing heat Effects of Heat Heat affects matter in different ways. The major effects of heat are as follows: Fact File Electricity obtained from the water is called hydroelectricity.
Oasis School Science and Technology -5 153 1. Heat changes the state of matter. 2. Heat changes the volume of matter. 3. Heat changes the temperatures of matter. 1. Heat changes the state of matter. Matter exists in three forms, viz. solid, liquid and gas. The physical state of a substance can be changed by heating or cooling. For example, water can be converted into steam (gas) by heating and steam can be converted into water (liquid) by cooling. On the other hand, water can be converted into ice (solid) by cooling and ice can be converted into water on heating. Change of a substance from one physical state to another is called change of state. Ice (Solid) Heat Heat Cool Water (Liquid) Cool Steam (gas) Metals like iron, copper, gold, silver, etc. melt on heating. Similarly, wax, plastic, butter, etc. also melt on heating. Conversely, the liquid state of those substances changes into solid on cooling. Activity 1 To demonstrate that solids melt on heating • Take an ice-cube and keep it on a plate. • Place the plate in the sun and observe. What happens? • Take a piece of wax and bring it near the flame of the burner. What happens? What can you conclude from these activities? Activity 2 To convert ice into water and water into vapour • Take some ice-cubes in a beaker. • Keep the beaker over the flame of the burner and observe the icecubes. The ice cubes melt and change into water. • Heat the beaker continuously Does water change into vapour? What is the conclusion of this activity?
154 Oasis School Science and Technology -5 2. Heat changes the volume of matter. Substances expand on heating and contract on cooling. Solid, liquid and gas all expand on heating. When an object absorbs more heat, its molecules vibrate with more energy These molecules require more space to vibrate. As a result, the object expands. Among three forms of matter, expansion is least in solids. Liquids expand less than gases and the substances in the gaseous state expand the most. The volume of solid, liquid and gas increases on heating. This process is called thermal expansion. 3. Heat changes the temperature of the matter Objects can absorb and release heat. When an object absorbs heat, it temperature increases. When an object releases heat, its temperature decreases. Thermometer measures the temperature of a matter. Expansion of Solids Solids have a definite shape and size. Stone, wood, brick, ice, wax, plastic, etc. are some examples of solids. When solids are heated, they show an increase in length, area and volume. It means that when solids are heated, they expand in all directions. When wax, ice, butter, plastic, etc. are heated, they melt into liquid. In the Himalayan region, snow and ice melt due to the heat of the sun and form water. Similarly, the telephone cables and electric cables fitted between the poles become loose during summer due to the heat of the sun. Have you observed the melting of ice or wax? What happens when ice and wax melt? When a solid is heated, it changes into liquid.
Oasis School Science and Technology -5 155 Activity 3 Bring a copper wire and slip an iron ring through the wire. Take two stands and stretch the wire between them as shown in the fig. (a). The wire should be straight when stretched tightly. copper wire I I metal ring stand Fig: (a) Copper wire before heating Bring a Bunsen burner and heat the copper wire for 5 - 10 minutes near the metal ring figure below. What happens to the wire after heating ? Observe carefully. Fig: (b) Copper wire after heating When the wire is heated for 5 - 10 minutes, it can be observed that the wire becomes loose as indicated by the metal ring. The length of the wire increases on heating and hence it becomes loose. This activity proves that solids expand on heating. Activity 4 Bring a candle and light it. Observe the burning candle and answer the following questions. • Is the thread of the candle burning? Is the wax of the candle melting? • Is the melted wax falling down? • What is the physical state of the wax that falls down after melting? • What can you conclude from this activity? Wax melting
156 Oasis School Science and Technology -5 Experiment Gravesend's Ball and Ring Experiment Object: To prove that solids expand on heating and contract on cooling Materials required: Stand, metallic ball and ring, Bunsen burner, thread, match box Procedure Bring a metallic ball and a metallic ring as shown in the figure below. Please note that the metallic ball is of the size that just passes through the ring at room temperature. Pass the ball through the ring as in figure below. Stand Thread Ring Metallic ball Metallic ball Fig: Before heating Fig: After heating Now, heat the ball for 10-15 minutes by a Bunsen burner and try to pass the ball through the ring as before. But, it can be observed that the heated ball does not pass through the ring. • The diameter of the ball increases so the size of the metal ball becomes greater than the size of the ring. As a result, the metal ball does not pass through the ring. This experiment also proves that solids expand on heating. • If the metal ball is allowed to cool down, it regains its original size. As a result, the metal ball can easily pass through the same ring. This experiment also proves that solids contract on cooling. Conclusion From this experiment, it can be concluded that solids expand on heating and contract on cooling.
Oasis School Science and Technology -5 157 Expansion of Liquids Like solids, liquids also expand on heating. Water, alcohol, milk, petrol, kerosene, etc. are some examples of liquids. When liquids are heated the free space and distance between particles increase. As a result, liquids expand more than solids. Experiment Object: To prove that liquids expand on heating and contract on cooling Materials required: Stand and clamp, round bottom flask, glass tube, cork, coloured water, Bunsen burner, tripod stand, wire gauze, marker Procedure • Bring a round bottom flask and fill it with coloured water. • Put a glass tube in the flask and fit the cork on the mouth of the flask. • Keep the flask on the wire gauze kept on the tripod stand and set the apparatus as shown in the figure below. • Mark the initial level ‘P’ in the glass tube and heat the flask with a Bunsen burner. What do you observe? • Remove the Bunsen burner and allow the liquid to cool down. What do you observe? Observation When the flask is heated, it is observed that the level of water at first falls slightly to ‘Q’. It is because the round bottom flask expands before the water kept inside it as the flame of the burner is in direct contact with the flask.
158 Oasis School Science and Technology -5 Glasst ube Cork R( Finall evel) P( Initiall evel) Q( levelf alls in the beginning) Coloured water Stand Round bottom flask Wire gauze Tripods tand Bunsen burner Fig: Experiment showing thermal expansion of gas After heating for some time, the level of water starts rising and the water level rises steadily upto point R in the glass tube. On further heating, the heat is transferred from the flask to the liquid (water). The liquid expands on heating and the level of water rises to level ‘R’ which is above the level P. It not only shows liquid expands on heating but also that liquid expands much more than the container. When the burner is removed and the liquid is allowed to cool down, the level of the liquid again comes back to its original level ‘P’. The liquid contracts on cooling and regains its previous level. It shows that liquid contracts on cooling. Conclusion From this experiment, it can be concluded that liquids expand on heating and contract on cooling. Expansion of Gases Air, nitrogen, oxygen, carbon dioxide, water vapour, etc. are gases. Gases are generally colourless and invisible. Like solids and liquids, gases also expand on heating. In gases, molecules are free to move and the force of attraction among the gas molecules is almost zero. Therefore, gases expand the most.
Oasis School Science and Technology -5 159 Experiment Object: To prove that gases expand on heating Materials required: Glass bottle, balloon, thread, water trough, hot water Procedure • Bring an empty glass bottle and fit a balloon to its neck as shown in the figure below. • Now, put the bottle in the water trough containing hot water. The hot water should cover at least two-thirds portion of the glass. Observe the balloon for a few minutes. What do you observe? • After a while the balloon is inflated. The empty bottle contains air and when it is kept in hot water, the air present inside the balloon gets heated and expands. The expanded air enters the balloon. As a result, the balloon gets inflated. Fig: Experiment showing thermal expansion of gas Conclusion This experiment proves that gases expand on heating. Absorption of Heat When we stand in the sun for a while we feel hot. If we touch our hair, it feels warm. If we touch our clothes, they also become hot. All types of Fact File Black objects absorb heat effectively than that of light coloured objects.
160 Oasis School Science and Technology -5 substances absorb heat. When a body absorbs heat, it becomes hot and when a body loses heat it becomes cold. Some objects absorb heat fast while others absorb heat slowly. It depends on the nature and colour of the object that absorbs heat. For example, the substances having black colour absorb heat faster than the substances having white colour. Activity 5 To demonstrate the absorption of heat • Take card board papers of black, white, green, red and blue colour. Make a small bag of each of the papers. • Take five thermometers and insert the bulb of the thermometer in each of the paper bags. • Now, keep all the paper bags on a table in the sun. • Record initial reading of each thermometer and note it down. Now, record the rise in temperature after every five minutes and fill in the given table. S.No. Paper bag Initial temp. Rise in temperature after 5 min. 10 min. 15 min. 20 min. 1. Black 2. White 3. Green 4. Red 5. Blue Which paper bag has the maximum temperature? What can you conclude from this activity? Advantages of Heating Effect Effect of heat over matters have different advantages in our daily life. Some of the advantages are mentioned below. i. It helps the food cooked properly. ii. Stopper of jammed bottle can be expanded using hot water and removed. iii. We can measure the temperature of any object using thermometer.
Oasis School Science and Technology -5 161 iv. Travelling on hot air balloon is possible. v. It helps fixing iron rim with the wooden wheel. vi. Smoke moves upward in the sky. vii Water cycle occurs due to this effect. viii.Metals can be shaped according to our need. Disadvantages of Heating Effect Effect of heat over matters is always not beneficial to us. Some of the disadvantages of heating effect are: i. Overflow of milk and other fluids while heating causes loss. ii. We need refrigerator to avoid change of ice to water. iii. It causes change in the composition of matter by resulting chemical change in them. iv. Rubber expansion joints are to be used in bridges to avoid expansion. v. Cracking of a thick glass tumbler due to hot water. vi. Heat can cause the electric wires in electric poles to sag during summer season. Utilities/Uses of Heat Heat is an important part of our lives. Human beings, plants and animals need heat or warmth to live. We use heat for various purposes. Some of the major utilities of heat are mentioned below: 1. Heat is used for making our body warm. We feel very cold in winter. Our body loses heat energy during winter and we feel cold. So, heat is used to keep our body warm. In rural areas, people obtain heat by burning substances like firewood, charcoal, kerosene and LP gas to keep their body warm. In urban areas, people use electric heaters and gas heaters to keep their body warm. Similarly,we go in the sun in the winter for making body warm
162 Oasis School Science and Technology -5 2. Heat is used for cooking food. Food cannot be cooked without heat energy. We get heat from firewood, coal, kerosene, bio-gas, LP gas, etc. for cooking food. Cooked foods are tasty and easy to digest. Most of the foods are cooked except fruits. 3. Heat is used for drying clothes. The heat energy of the sun is used for drying wet clothes. The water in the wet clothes changes into vapour due to the heat of the sun. As a result, the wet clothes become dry. Clothes dry faster in a sunny day than in a cloudy day. 4. Heat is used in industries to produce various substances. In industries, heat is used to produce different substances like cement, iron rods, plastic, biscuit, chocolate, etc. In industries, heat is obtained from electricity, coal, firewood, LP gas, etc. 5. Heat is used to purify water. Natural water may contain germs. So water is boiled by heating to kill germs. 6. Heat is used to dry cereals, pulses, fish and meat. The heat of the sun is utilized to dry various food items like cereals, pulses, fish and meat before storing them. Fig: Sun drying of clothes
Oasis School Science and Technology -5 163 Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. Which is the source of energy that helps to produce other sources of energy? a. Sun b. Electricity c. Fire d. Fossil fuel Answer: The sun is the source of energy that helps to produce other sources of energy. 2. Define the term thermal expansion? The process of increase in the volume of the substances on heating it is called thermal expansion. 3. Identify which of the following statements are true. a. Heat expands the volume of gases. b. Liquid can change into gases but not to solids. c. Fossil fuels are obtained from hydro-electric stations. d. Fuel-wood is an example of bio-fuel. e. Temperature of a body increases on heating. Answer: a and e 4. List out three major effects of heat. Three major effects of heat are: a. Heat changes the state of matter. b. Heat changes the volume of matter. c. Heat increases the temperature of matter. 5. Why do gas expand most on heating? Molecules of gases have very weak force of attraction and are free to move. Heat provide energy to them to move farther. Due to this reason gas expands most than other matters. 6. Mention any three differences between fossil fuel and hydroelectricity. Three differences between fossil fuel and hydro-electricity are given below.
164 Oasis School Science and Technology -5 Fossil Fuel Hydro-electricity a. It is obtained from fossils. a. It is produced from moving water. b. Fossil fuels on burning provide heat energy. b. Electrical appliances like heater should be used to convert electricity into heat energy. c. It is natural energy source. c. It is artificial energy source. Exercises 1. Choose the best answer from the given alternatives. a. The form of energy which gives us the sensation of warmth is called ____________. i. Light ii. Heat iii. Temperature iv. Electricity b. Which of the following is the main source of heat energy? i. Sun ii. Electricity iii. Fire iv. Fossil fuel c. Which of the following is the bio-fuel energy? i. Petrol ii. Firewood iii. LP gas iv. Coal d. Which of the following is the pollution-free source of heat energy? i. Firewood ii. Coal iii. Kerosene iv. Hydroelectricity e. Which of the following is not a source of heat? i. Sun ii. Moon iii. Coal iv. Firewood
Oasis School Science and Technology -5 165 f. Natural gas is obtained form _________. i. Animal dung ii. Blowing wind iii. Petroleum mines iv. Firewood 2. State which of the following statements are true and which are false. a. Electricity is the major source of heat energy. b. Bio-fuel is obtained from cow dung. c. Coal and petrol are called fossil fuels. d. Heat cannot change the states of matter. e. Water changes into steam on heating. f. Heat is used for cooking food and drying clothes. 3. Fill in the blanks with appropriate words. a. The sun is the main source of ………… and …… energy . b. Heat is measured in …… and …… c. Heat can be …… from one form to another. d. Sun, bio-fuel and fossil fuel are …… of heat e. Heat changes ……… and ……… of matter. f. The volume of solid, liquid and gas …… on heating. g. Water changes into ice on ……… 4. Give very short answers to the following questions. a. Which energy is needed for thermal expansion of matter? b. Name any two fossil fuels. c. List any four sources of heat energy. d. Which form of matter expanse more among soilds, liquids and gases? e. Name two devices that convert electricity energy into heat energy.
166 Oasis School Science and Technology -5 f. What happens when: i. Water is heated ii. Water is cooled iii. Ice is heated 5. Give reasons. a. Wood is an example of bio-fuel. b. People prefer white clothes in summer and black clothes in winter. c. Jammed stopper of a bottle is dipped into hot water. 6. Differentiate between : a. Bio-fuel and fossil fuel b. Thermal expansion of soilds and gases 7. Answer the following questions in short. a. What is heat? In which units is it measured? b. What do you mean by sources of heat? Name any four sources. c. Define fossil fuels with three examples. d. State the meaning of bio-fuel with two examples. e. List any two major effects of heat. f. Illustrate the need of heat in three points. 8. Answer the following questions in short. a. Demonstrate that the solids expands on heating. b. Discuss an experiment showing gas expands on heating. 9. Draw a schematic diagram of showing change in state of water on heating and cooling.
Oasis School Science and Technology -5 167 Key terms and terminologies 1. Mixture : Mixture is a mass which is obtained by mixing two or more substances in any proportion by weight. 2. Homogeneous mixture: The mixture in which mixing components are distributed uniformly and they cannot be identified by naked eyes is called homogeneous mixture. 3. Heterogeneous mixture: The mixture in which mixing components are not distributed uniformly and they can be identified by naked eyes is called heterogeneous mixture. UNIT 6.3 MIXTURE Estimated teaching periods Theory 8 Practical 2 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) The Sequence of Curriculum Issued by CDC 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 atom lasers, atomic clocks and gravitational, rotational or magnetic sensors with excellent sensitivity. About the Scientist Satyendra Nath Bose
168 Oasis School Science and Technology -5 4. Separation of mixture: The process by which the components of a mixture are separated from each other is called separation of mixture. 5. Components of mixture: The substances which are mixed together to make a mixture are called components of a mixture. 6. Sedimentation : The process of settling down of heavier components of the mixture at the bottom of the vessel is called sedimentation. 7. Decantation : The process in which the clear liquid is poured into another vessel without disturbing the sediment is called decantation. 8. Residue : The clear liquid collected after filtration is called filtrate and the solid particles collected in filter paper is called residue. 9. Winnowing : The method of separating the mixture of light and heavy solid particles with the help of air is called winnowing. 10. Sieving : The method of separating the mixture of solid particles of different size by using a sieve is called sieving. 11. 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 coats in rice, sand in rice, sand in lime, dust particles in air, etc. are some examples of mixture. So, a mixture is a mass which is obtained by mixing two or more substances in any proportion by weight.
Oasis School Science and Technology -5 169 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 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 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: i. Homogeneous mixture ii. Heterogeneous mixture i. Homogeneous mixture The mixture in which mixing components are distributed uniformly and they cannot be identified by naked eyes is called homogeneous mixture. For example, sugar solution, salt solution, etc. In sugar solution, sugar particles are distributed uniformly throughout the water. Similarly, in salt solution, salt is uniformly distributed in water. Fig: Sugar solution
170 Oasis School Science and Technology -5 ii. Heterogeneous mixture The mixture in which mixing components are not distributed uniformly and they can be identified by naked eyes is called heterogeneous mixture. Rice coats in rice, sand in rice, muddy water are some examples of heterogeneous mixtures. Differences between Homogeneous and Heterogeneous mixture S.N. Homogeneous mixture S.N. Heterogeneous mixture a. In this mixture, mixing components are distributed uniformly. a. In this mixture, mixing components are not distributed uniformly. b. We cannot see all the mixing components. For example, salt solution, brass, etc. b. We can see the mixing components. For example, muddy water, stones in rice, etc. Importance of mixture Mixtures play a significant role in our daily life as they are prepared for various purposes. The importance of mixture is given below: 1. Mixture of tea leaves, sugar, milk and water is made to prepare tea. 2. Mixture of glucose and water is made for drinking. 3. Mixture of different colours is used in painting. 4. Mixture of cement, sand, water and gravel is used for construction works. 5. Medicines are made by mixing various chemicals. 6. Plants absorb various nutrients from the soil in the form of mixture. Fig: Sandy water
Oasis School Science and Technology -5 171 Methods of separating of mixtures Mixture is formed by combination of two or more substances at any ratio by weight. The substances which are mixed to form a mixture are called components of the mixture. The process by which the components of a mixture are separated from each other is called separation of mixture. 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, we will learn some common methods of separating mixtures, viz. sedimentation and decantation, filtration, winnowing, sieving and magnetic separation. 1. 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 sediments settle at the bottom of the container. Then the clear liquid is gently poured into another vessel without disturbing the sediments. This method is also applied to separate the mixture of two liquids having different density. The process of settling down of heavier components of the mixture at the bottom of the vessel is called sedimentation. The heavier and insoluble particles of a mixture are called sediments. The process in which the clear liquid is poured into another vessel without disturbing the sediment is called decantation. Fact File Sedimentation and decantation can only be used for mixtures in which component of mixtures settle in the layers.
172 Oasis School Science and Technology -5 Activity 1 Objective: To separate sand and water from their mixture Materials required: Two beakers, a glass rod, sand, water Procedure • Prepare a mixture of sand and water by mixing them at any ratio. • Leave the mixture undisturbed for some time. • Pour the clean water into another vessel gently using a glass rod without disturbing the sediment. Fig: Sedimentation and Decantation 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 sediments. Conclusion: Sediment, i.e. sand is left in one beaker and clear liquid is collected in another beaker. In this way, components of the mixture are separated by sedimentation and decantation. 2. 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 mixture in which the components of the mixture are separated by using 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 Fig: Filtering tea
Oasis School Science and Technology -5 173 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 particles collected in filter paper is called residue. Generally, filter paper is used in filtration process in laboratory. Before using the filter paper, it is folded to make a cone as shown in the following figure. Fig: Steps of folding a filer paper Activity 2 Objective: To separate mud and water from muddy water Materials required: Two beakers, glass rod, stand, funnel, filter paper, mud, and water Procedure • Prepare a mixture of mud and water in a beaker. • Fold the filter paper into a cone. • Put the cone shaped filter paper in the funnel and arrange the apparatus as shown in the given diagram. • Pour the mixture in the funnel gently with the help of a glass rod. Observation You will see the clear droplets of water falling down from the lower part of funnel into the beaker. The solid particles or residue remains on the filter paper. Conclusion The mixture of mud and water can be separated by filtration method. As a result, the clear liquid is collected in one vessel and solid particles, i.e. mud on the filter paper. Muddy water Filter paper Funnel Residue Stand Filtrate Fig: Filtration Fact File Filtration cannot separate components of mixture in a homogeneous solution.
174 Oasis School Science and Technology -5 3. Winnowing The method of separating the mixture of light and heavy solid particles with the help of air is called winnowing. Husk from rice, rice coats from rice, stone particles from rice, etc. can be separated by this method. Winnowing is used to separate lighter and heavier components of a heterogeneous mixture. For example, husk in rice. In the above example, husk is a lighter component and rice is a heavier component. By using winnowing method farmers separate husk from rice in rural areas. 4. Sieving In some mixtures, the size of mixing particles differs from each other. In this condition, sieving is used to separate the components of the mixture. The method of separating the mixture of solid particles of different size by using a sieve is called sieving. In sieving method, we use a special type of device called sieve. It contains a large number of pores. The size of all pores for one sieve is about the same. For sieving, we keep the mixture on the sieve and shake the sieve gently. The particles which are smaller than the size of pores of the sieve fall down from the sieve and the particles bigger than the size of the pores of the sieve remain on the sieve. This method is used to separate corn and millet, pebbles and sand, wheat and flour, etc. Fig: Winnowing Fig: Sieving
Oasis School Science and Technology -5 175 5. 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 non- magnetic substances and the magnetic substances can be separated from the mixture. Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. Which of the following is an example of heterogeneous mixture? a. Salt water b. Sugar water c. Mudywater d. Cocacola Answer: Mudywater is an example of heterogeneous mixture. 2. Define winnowing. What does it separate? The method of separating the mixture of light and heavy solid particles with the help of air is called winnowing. It separates rice grains from husks. 3. Which of the following statements is true? a. Components of mixture can be separated by naked eyes in homogeneous mixture. b. Magnetic separation separates wood dust from wood. c. Filter paper is used to filter tea leves from tea in home. d. Clear liquid collected after filtration is called filtrate. Sulphur Iron filings Magnet Mixture of iron and sulphur Fig: Magnetic separation
176 Oasis School Science and Technology -5 Answer: Clear liquid collected after filtration is called filtrate. 4. Why magnetic separation cannot be used to separate water and sand from their mixture? Magnetic separation cannot be used to separate water and sand from their mixture because both water and sand are non-magnetic substances. 5. Differentiate between sieving and winnowing. Differences between sieving and winnowing are given below. Sieving Winnowing a. It is the process of separating different sized solid particles from the mixture. a. It is the process of separating heavy and light solid particles from the mixture. b. Sieve of different pore sizes are used in this process. b. Wind or air current is used in this process. c. Example is separating pebbles from sand. c. Example is separating husk from rice grains. 6. Identify the methods for separating the following mixtures. a. Pebbles and water b. Iron particles from sand c. Coarse grain gravels and fine grain gravels Answer: a - Sedimentation and decantation b - Magnetic separation c - Sieving Exercises 1. Choose the best answer from the given alternatives. a. Which of the following is a homogeneous mixture? i. Salt and water ii. Sand and water iii. Soil and water iv. Sand and salt
Oasis School Science and Technology -5 177 b. Which of the following is a heterogeneous mixture? i. Milk 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. Seiving iv. Magnetic separation d. The mixture of iron filings and sand can be separated by ____. i. Sedimentation ii. Magnetic separation iii. Sieving iv. Filtration e. The method of separating husk from rice is called __________. i. Filtration ii. Sieving iii. Winnowing iv. Decantation 2. Fill in the blanks with appropriate words. a. The combination 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 non- magnetic substances. d. ………………….is used to separate bigger and smaller solid particles from the mixture. e. The solid substance collected in filter paper is called …………………... f. The process of pouring the clear liquid into another vessel without disturbing sediment is called ………………. 3. Write True or False at the end of each statements. a. The mass formed by mixing two or more substances in any ratio is called mixture. b. The mixture in which the components are uniformly distributed throughout the mixture is called homogeneous mixture.
178 Oasis School Science and Technology -5 c. Filtration is the process in which the heavier particles of mixture settle down at the bottom of the vessel. d. The clear liquid collected after filtration is called residue. e. The mixture of wheat and flour can be separated by winnowing. 4. Give very short answers to the following questions. a. What type of mixture have mixing components dissolved uniformly? b. What is the name of device with pores that is used for sieving? c. Which substance is needed to separate mixtures of sand and iron particles? d. What do you think which method is applicable to separate wood dust from wood chunks? 5. Name the methods of separating mixtures. a. b. 6. 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. Sedimentation and decantation make filtration easy and fast. 7. Write any two differences between: a. Homogeneous and Heterogeneous mixture b. Sieving and Filtration c. Sieve and Filter paper d. Magnetic separation and winnowing 8. Answer the following questions in short.
Oasis School Science and Technology -5 179 a. Define 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 a heterogeneous mixture? Write any two examples. e. Write any four importance of mixture. f. What are the components of a mixture? Explain with examples. g. Define filtration. Draw a well labelled diagram of filtration process. h. What is 'sedimentation and decantation'? Explain it with a well-labelled diagram. i. In which condition do we use winnowing method of separating mixture? j. What is a sieve? Why is it used? k. What are magnetic substances? Write any two examples. l. In which condition do we use magnetic separation? 9. Identify the method of separating the components of the following mixtures. a. Wheat and flour b. Muddy water c. Sand and iron filings d. Tea leaves and tea e. Husk and rice f. Sand and water 10. Answer the following questions. a. Define the process of separation of mud and water using filtration process. b. Explain magnetic separation of sand and iron particles. c. What could be the other mixture separating processes that we use in our home. Explain them in short. 11. Draw the correct sketch forfolding filter paper with explanation. 12. Draw the labelled schematic diagram of filtration process.
180 Oasis School Science and Technology -5 7 ENERGY UNIT
Oasis School Science and Technology -5 181 UNIT 7.1 LIGHT Estimated teaching periods Theory 6 Practical 2 Sources of light Luminous and non-luminous bodies Transparent, translucent and opaque objects Colours of light The Sequence of Curriculum Issued by CDC Antonie van Leeuwenhoek is a Dutch microscopist. He was born in 1632 and died in 1723 in The Netherlands. He invented simple microscope capable of studying microorganism, 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. About the Scientist Antonie van Leeuwenhoek Key terms and terminologies 1. Light : light is a form of energy which causes the sensation of vision. 2. Luminous objects : The objects having their own source of light for shining are called luminous objects. 3. Non-luminous objects: The objects which do not have their own source of light for shining are called non-luminous objects. 4. Transparent objects : The objects that allow light to pass through them are called transparent objects. 5. Translucent objects : The objects which allow only a part of light to pass through them are called translucent objects. 6. Opaque objects : The objects that do not allow the light to pass through them are called opaque objects.
182 Oasis School Science and Technology -5 Introduction We see various things around us during day but we cannot see things in a dark room even though we keep our eyes open. But every object in the room becomes visible as soon as we switch on a tube light. So, light is a form of energy which causes the sensation of vision. Light is essential for life on the earth. Green plants need sunlight to prepare food. Human beings depend on light energy for requirements of food, oxygen and fuel. Sources of Light Some objects like the sun, burning candle, lantern, glowing bulb, etc. emit light and make things visible. These objects are called sources of light. The objects that give out light are called sources of light. The major sources of light are given below: 1. Sun: The sun is the major natural source of light. Things are visible during the day due to the presence of sunlight. We cannot see things at night as sunlight is absent at night. No object gives light on the earth as much as the sun. Therefore, the sun is called the major source of light energy. 2. Electricity: Electricity is also the main source of light. Electric bulb, tube light and CFL convert electrical energy into light energy. We get light energy from electricity at night. It is easy and safe to obtain light from electricity. In cities and developed countries, light is obtained from electricity. 3. Lamp: Lantern, torchlight, candle, kerosene lamp, etc. are also the sources of light. These sources of light are mostly used in rural areas of Nepal. Fig: Sunlit room Fig: Light from electricity
Oasis School Science and Technology -5 183 Burning candle Kerosene lamp Lantern Torch light 4. Moon: The moon is the natural source of light at night of the bright half. The moon gives maximum light at full moon night. But the moon gives very less light than that given by the sun. The light given by the moon is not sufficient to read and write. However, we can walk easily in the moonlight. Luminous Objects Objects such as the sun, a burning candle, fire, etc. emit light of their own. These objects are called luminous objects. The objects having their own source of light for shining are called luminous objects. For example, sun, star, glowing bulb, etc. Non-luminous Objects Objects such as brick, table, chair, book, wood, etc. do not emit light themselves. These objects are called non-luminous objects. The objects which do not have their own source of light for shining are called nonluminous objects. For example, book, chair, glass, stone, ball, moon, earth, etc. The moon does not have its own source of light. So, it is called a nonluminous object. The light from the sun falls on the moon and the moon reflects the sunlight and becomes visible. Non-luminous objects are mainly of three types, viz. transparent, translucent and opaque objects. Fig: Light from the moon
184 Oasis School Science and Technology -5 Transparent, Translucent and Opaque Objects We are surrounded by numbers of objects. Some objects can pass light completely through it while some do not. On the basis of their ability to pass light through them, they are classified as transparent, translucent and opaque objects. Transparent objects Some objects like glass, air, water, etc. allow light to pass through them. These objects are called transparent objects. The objects that allow light to pass through them are called transparent objects. For example, glass, water, air, clean plastic, etc. Transparent objects are used in window, green house, showcase, lens, glasses utensils, etc. Translucent objects The objects which allow only a part of light to pass through them are called translucent objects. For example, tracing paper, ground glass, white paper immersed in oil, etc. Translucent objects form faint images. We cannot see things clearly while viewing through translucent objects. Translucent objects are used to control the passing of light usually in decorative glasses, bathroom window, room partitions, curtains, etc. Opaque objects The objects that do not allow the light to pass through them are called opaque objects. For example, book, table, wood, soil, stone, chair, brick, etc. Opaque objects form dark images as light does not pass through them. Fig: Light in transparent, translucent and opaque objects
Oasis School Science and Technology -5 185 Opaque objects are used for blocking lights. They are used in wooden windows, doors, wall, x-ray room, photographic room etc. Colours of Light Have you noticed the curved faint colourful bands after rain during daytime? If yes, you have seen a rainbow. Can you name the colours seen in the rainbow? Do you know how the rainbow forms? A rainbow is made up of seven colours. They are red, organge, yellow, green, blue, indigo and violet. To see the rainbow in the horizon some conditions are necessary. i. The sun needs to be behind the viewer. ii. The sun needs to be low in the sky. iii. Rain, fog or some other source of water droplets must be in front of the viewer. From the above condition we can understand that the rainbow is the colour from sunlight. It forms when the water droplets in the air scatters sunlight. It means the sunlight is made up of seven different colours. Have you seen the scattering of light elsewhere apart from rainbow. If yes share with your friends. Fig: Colours of rainbow Fact File The sunlight is the visible light which is also known as white light. It is made up of 7 colours voilet, indigo, blue, green, yellow, orange and red.
186 Oasis School Science and Technology -5 Activity 1 • Observe various objects in your surroundings and classify them in terms of luminous and non-luminous objects. Activity 2 • Collect various objects such as a piece of glass, plastic, wooden board, mirror, tracing paper, white paper, etc. • Keep those objects one by one in the sunlight and observe whether they form an image or not, which object allows light to pass through it and which does not. • On the basis of your observation, classify these objects in terms of transparent, translucent or opaque objects. Activity 3 Take a glass prism and white paper. Place the prism in any hand or paper in such way that one face faces the sunlight and another faces the white paper. What did you see in the paper? How many colour bands do you see? Name them. What is the conclusion of the activity? Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. What type of object is moon? a. Trasparent b. Translucent c. Luminous d. Non-luminous Answer: The moon is a non-luminous object. 2. What gives the sensation of vision? a. Heat b. Light c. Electricity d. Fire
Oasis School Science and Technology -5 187 Answer: Light gives the sensation of vision. 3. Define transparent objects with examples. The objects that allow light to pass through them are called transparent objects. Air, water, clear glass and plastic sheets are some examples of transparent objects. 4. Why stars are known as luminous objects? Stars are known as luminous objects because they can produce their own light. 5. Identify the following as transparent, translucent and opaque objects Woden wall, clear plastic sheet, muddy water, sugar solution, coloured glass, coloured plastic sheet, clean air, thick paper i. Transparent: clear plastic sheet, clean air, ii. Translucent : muddy water, iii. Opaque objects : Woden wall, thick paper 6. Differentiate between transparent and opaque objects. The differences between transparent and opaque object are given below. Transparent Object Opaque Object a. It allows passing of light through them. a. It blocks light completely. b. It does not form shadow. b. It forms dark shadow behind it. c. Examples are clean water, clean air, normal glass etc. c. Examples are book, wall, bag, etc.
188 Oasis School Science and Technology -5 Exercises 1. Choose the best answer from the given alternatives. a. Light is a form of energy which causes the ____________. i. sensation of vision ii. sensation of heat iii. sensation of sound iv. sensation of cold b. Which of the following is the major source of light? i. Electricity ii. Candle iii. Sun iv. Moon c. Which of the following is a luminous body? i. Sun ii. Star iii. Burning candle iv. All of these d. Which of the following is a non-luminous body? i. Moon ii. Burning candle iii. Firefly iv. Sun e. The object that allows light to pass through it is called ......................... i. luminous object ii. translucent object iii. opaque object iv. transparent object 2. Fill in the blanks with appropriate words. a. Light causes the sensation of ……… b. …… is the main natural source of light. c. The object that gives light is called the ……… of light. d. The object which allows light to pass through it is called ……… 3. Write True or False. a. The sun is the main source of light energy. b. The object having its own source of light is called non-luminous object. c. Moon is a luminous body. d. Glass and water are transparent objects. e. Brick and book are opaque objects. 4. Give very short answers to the following questions. a. Which energy provides us the sense of vision?
Oasis School Science and Technology -5 189 b. Which is luminous object between the sun, the earth and the moon? c. Which types of objects create dark shadow behind them? d. Which type of objects does not create shadow behind them? e. What type of object is the window in your classroom? 5. Give reasons. a. Moon shines but it is a non-luminous object. b. Wooden plank is an opaque object. c. Clean water is transparent. d. Sun is a luminous body. 6. Differentiate between: a. Luminous body and Non-luminous body b. Transparent object and Translucent object c. Translucent object and Opaque object 7. Answer the following questions in short. a. What is light? b. What is meant by the source of light? Give any two examples. c. What are luminous objects? Give any two examples. d. What are non-luminous objects? Give any three examples. e. Define transparent objects with any two examples. f. Define translucent objects with any two examples. g. What do you mean by opaque objects? Give two examples. 8. Identify the following objects as luminous and non-luminous objects. Stars, Ball, Candle, LED bulb, Shining plate, Mirror, Gold 9. Answer the following questions. a. All the sources of light may not be luminous objects. Justify this statement with a suitable example. b. Make the list of transparent, translucent and opaque objects available in your home.
190 Oasis School Science and Technology -5 Key terms and terminologies 1. Sound : Sound is a form of energy which produces a sensation of hearing in the ears. 2. Musical sound : The sound that produces pleasing effect on our ears and mind is called a musical sound. 3. Noise : The sound that produces unpleasing effect on our ears and mind is called noise. 4. Pitch : The shrillness of a sound is called the pitch of the sound. 5. Loudness : Loudness is the characteristic of a musical sound by which a loud sound can be distinguished from a faint sound. 6. Wave : The disturbance in a medium that carries UNIT 7.2 SOUND Estimated teaching periods Theory 6 Practical 2 Introduction to sound Sources of sound Musical sound and noise, and conditions in which are produced Shrillness and loudness of sound, and conditions in which they are produced Effects of noise and our activities to reduce noise The Sequence of Curriculum Issued by CDC 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. About the Scientist Alexander Graham Bell
Oasis School Science and Technology -5 191 energy without moving its particles is called wave. 7. Wave motion : Wave motion is a periodic disturbance travelling through a medium which is produced by a vibrating body. 8. Ripple : A small wave formed on the surface of liquid is called ripple. Introduction Every day we hear a variety of sounds like horn of vehicles, sound of school bell, barking of a dog, chirping of birds, sound of a teacher, sounds of musical instruments and so on. We produce sound while talking and communicating with others. All 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. Sources of Sound Sound is produced due to the vibration of the solid, liquid and gas. A vibration is a rapid back and forth motion of a particle about its mean position. Every vibrating body is a source of sound. A vibrating body which produces sound is called a source of sound. Temple bell, radio, cassette player, television, horn of vehicles, musical instruments, etc. are some sources of sound. Sound travels in all directions and needs a medium for propagation. Bell Radio Drum Set Fig: Sources of sound
192 Oasis School Science and Technology -5 Activity 1 • Press your throat with your fingers and sing a song or speak for 10-15 seconds. What do you feel on your fingers? You will feel the vibration in your fingers. • Now, stop singing or speaking for 5-10 seconds. Can you feel vibration? • When there is vibration, sound is produced and when vibration stops, the sound also stops. So we can produce sound by vibrating our vocal cord. Activity 2 • Bring a 'madal' and keep it in the vertical position so that its leather surface remains horizontal. • Now, place some powder over the surface of the leather and bang lightly on the leather. What do you observe? • You will observe that the powder vibrates due to the vibration of the leather and the vibration of the leather produces sound. Fig: Madal Activity 3 • Bring a plastic whistle and observe it carefully. You can see a small ball inside it. • Now, blow the whistle. You will hear the sound produced by the whistle. This sound is produced due to the vibration of the ball of the whistle. When the ball of the whistle stops vibrating, the sound also stops. Fig: Blowing a whistle
Oasis School Science and Technology -5 193 Characteristics of Sound All sounds that produce the sensation of hearing are mainly divided into two types. They are: i. Musical sound ii. Noise i. Musical sound The sound that produces pleasing effect on our ears and mind is called a musical sound. It is continuous and uniform. For example, the sounds produced by musical instruments like guitar, piano, flute, madal, violin, etc. (a) (b) Fig: Musical sound ii. Noise The sound that produces unpleasing effect on our ears and mind is called noise. It is discontinuous and non uniform. For example, the sound produced by horn of vehicles, machines in a factory, sounds of people in a crowd, etc. Characteristics of Musical Sound A musical sound possesses the following characteristics: i. Pitch ii. Loudness i. Pitch of sound The voice of children and ladies is sharp as compared to the voice of men. Similarly, the voice of a girl is shrill as compared to that Fig: Sound pollution
194 Oasis School Science and Technology -5 of a boy. The shrillness of a sound is called the pitch of the sound. Pitch is the characteristic of a musical sound by which we can distinguish a shrill sound from a hoarse (grave) sound. The pitch of a sound cannot be measured but it can be felt. The sound produced by a vibrating object with a high frequency (i.e. number of vibrations per second) is called shrill or high-pitched. For example, the sound of a girl, the sound produced by thin strings of a guitar, the sound produced by wings of a mosquito, etc. Similarly, the sound produced by a vibrating object with a low frequency is called flat or low-pitched. For example, the sound of men, the sound produced by thick strings of a guitar, sound produced by leather of tabala when strings are loose, etc. Activity 4 • Take a bicycle and place it upside down as shown in the figure. • Turn the paddle with your hand slowly to rotate the wheel. • Now, take a cardboard and hold it between the rotating spokes. • Now, listen to the sound produced due to the vibration of the cardboard. • Increase the speed of rotation and listen to the sound produced. Fig: Bicycle upside down What do you observe? You will notice that higher the speed of rotation, higher is the frequency of vibration and higher is the pitch. The pitch of sound depends on the frequency of vibration. The higher the frequency, the more shrill is the sound.
Oasis School Science and Technology -5 195 Activity 5 • Take a cardboard box or tin box. Affix the rubber bands of different thickness as shown in the figure. • Now, pluck all the rubber bands one by one and listen to the sound produced. Which rubber band produces the sound with the highest pitch? • What can you conclude from this activity? Rubber bands Fig: Rubber bands on cardboard ii. Loudness of Sound If we strike a drum softly, its skin vibrates and produces a soft sound. On the other hand, a louder sound is produced when we strike the drum hard. When we shout, we use more energy and hence produce a louder sound. Similarly, when we whisper, we use less energy and hence produce a lower faint sound. Loudness is the characteristic of a musical sound by which a loud sound can be distinguished from a faint sound. Fig: Sources of sound with large vibrating area Loudness of sound depends on the energy that a wave carries. The greater the energy carried by the wave, the louder is the sound produced. The loudness of sound increases with an increase in the area of the vibrating body. For example, a large temple bell
196 Oasis School Science and Technology -5 produces a louder sound than a small one. Similarly, loudness of sound depends on the distance between the source of sound and the listener. The lesser the distance between the listener and the source, the louder is the sound heard by the listener. Activity 6 • Take a drum and strike its skin softly and listen to the sound. • Now, strike the skin hard and listen to the sound produced. In which condition is the sound louder? Is the pitch of the both sounds the same? What can you conclude from this activity? Activity 7 • Take the school bell and the hammer and go to the school ground with your friends. • Stand at a place and hold the bell. • Ask your friends to stand at a distance of 10 m each from the bell as shown in the figure. Fig: Activity for loudness of sound • Now, hit the bell softly and ask your friends to raise their hands if they hear the sound of the bell. • Hit the bell hard and observe how far the sound of the bell can be heard. • Write down the conclusion of this activity.