Beat the heat

1. Beat the heat Just feel the effects of heat By Bergin.G Based on 10th standard Tamilnadu State Board Syllabus

2. Contents

3. Learning objectives • Students understand, • Transfer of Heat Energy. • Specific heat capacity. • Principle of the method of mixtures. • The issues involved in Thermal expansion. • Effect of cooling in evaporation. • The principle and working of refrigerator. • The concept of latent heat. home

4. The Transfer of Heat Energy EXIT • If heat is removed, temperature of the water will decrease and the heat is transferred to the surrounding until both are at the same temperature. That is around 32o C When water is heated its temperature rises. Let us assume that its temperature be around 80oC and surrounding temperature is around 32oC. EXIT Click to view principle, and types of heat transfer

5. Conduction What is conduction ? • Conduction is the transfer of energy through matter from particle to particle. It can occur in solids. Every atom is physically bonded to its neighbours in some way. If heat energy is supplied to one part of a solid, the atoms vibrate faster. As they vibrate more, the bonds between atoms are shaken more. This passes vibrations on to the next atom, and so on. Eventually the energy spreads throughout the solid. The overall temperature has increased. EXIT Click to view what is conduction

6. Conduction Fun to do Direction of heat transfer Click on the below steps Clamp a brass rod as shown in the figure Attach some iron nails to the rod with the help of wax. Heat one end of the rod using a burner. What do you observe ? Discuss with your teacher.

7. Good and bad conductors THINK QUEST -1 THINK QUEST -2 THINK QUEST -3 THINK QUEST -4 Handles of cooking vessels and kettles are made of wood or plastic. Why? Cooking vessels are made up of metals. Why? Why we use woolen clothes in winter ? Copper tubes are used in automobile radiators ? Click here to get the hint Click here to get the hint Click here to get the hint Click here to get the hint wood or plastics are bad conductors Metals are good conductors of heat. Copper readily absorbs and conduct away heat from the hot water coming from the engine. The pores in the woolen clothes filled with air which is a bad conductor.. EXIT EXIT EXIT EXIT THINK QUEST - 5 Why ice boxes are double – walled conductors? Click here to get the hint Air in between the double wall is a bad conductor. EXIT

8. Convection in fluids What is convection? Convection is the mode of transfer of heat in fluids where the molecules actually move from one part of the fluid to the other. EXIT Convection in air Convection in water Click to view what is convection

9. Convection in fluids

10. Convection in fluids FACT FILE As molecules in solids are tightly packed actual moment of molecules is not possible in solids. Hence convection is not possible in solids. THINK QUEST -1 THINK QUEST -2 Why ventilators are constructed in a room ? Why chimneys are fitted in the factories ? EXIT Click here to get the hint EXIT Click here to get the hint EXIT To maintain fresh flow of air by convection current. The hot air took the smoke and poisonous gas from the factory and moves up. Do you Know? EXIT Click to view fact file , Do you know

11. Radiation I feel very hot EXIT Water man in front of a campfire feel hotness. Do you think this heat energy is by conduction or convection?. No, heat requires no medium to reach him from campfire. This mode of transfer of heat is called radiation Click to view what is radiation?

12. Radiation Some time heat energy is forcefully made to flow from a region of lower temperature to a region of higher temperature. To do this we need to supply energy to the system from outside. This outside source of energy is electrical energy. This concept is used in air conditioners and refrigerators. Let us imagine you are on the top of the earth I am throwing ozone particles to minimize radiation I want to minimize heat radiation reaching to earth surface. FACT FILE EXIT Click to view the fact file home

13. Specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of the substance through 1o C. Specific heat capacity Fun to do Click on the given steps Take 1 kg of water in a beaker Measure the temperature Water – 1kg Heat the water till the temperature raises through 1o C The amount of heat required to raise the temperature of the 1 kg of water through 1o c is called specific heat capacity of water

14. Specific heat capacity Water – 1kg Coconut oil – 1kg Take equal mass of water and coconut oil. Note their initial temperatures. Using the same burner heat the two beakers for five minutes. Observe that the rise in temperature is different for different liquids. The rise in temperature for two liquids are different. Why? Discus your observation with your teacher.

15. Specific heat capacity FACT FILE Amount of heat energy absorbed Among the liquids, the specific heat capacity is maximum for water and minimum for mercury. Hence water is used as a coolant in radiators of automobile engines and mercury is used as a thermometric liquid. THINK QUEST When a substance is heated the amount of heat energy absorbed (Q) by the substance is directly proportional to Mass of the substance (m) Specific heat capacity which is constant for a particular substance (s) Change in temperature (T) Q = m X s X T Why does a piece of water melon stay cool for a longer time than sandwiches when both are taken out from refrigerator on a hot day ? EXIT Click to view fact file home

16. Heat lost or gained by method of mixtures Click on the given steps Take some water in a beaker. Let m1 be mass of water and s1 be specific heat capacity of water. water m1 – mass S1 - specific heat capacity Take a metal ball. Let m2 be mass of metal ball and s2 be specific heat capacity of the metal Measure the temperature of water as t1. • Metal ball • m2 – mass S2- specific heat capacity • Metal ball • m2 – mass S2- specific heat capacity water m1 – mass S1 - specific heat capacity water m1 – mass S1 - specific heat capacity Heat the metal ball. • Metal ball • m2 – mass S2- specific heat capacity • Metal ball • m2 – mass S2- specific heat capacity Metal ball m2 – mass S2- specific heat capacity Now temperature be t2 Put the ball inside the water. Heat lost by the ball = m1 s1(t1 – t2) Heat gained by the water = m2 s2(t2 –t1) Heat lost by the ball = Heat gained by the water m1 s1(t1 – t2 ) = m2 s2(t2 – t1 ) home

17. Heat lost or gained by method of mixtures Amount of heat energy absorbed When two substances at different temperatures are mixed, heat flows from hot substance to cold substance, till both attain the same temperature. Provided no heat is received from or given to the surroundings and also if there is no chemical action in the mixture. When ice is mixed with water , ice absorb heat from water. When heated metal ball is put in a cold water , water absorb heat from the hot metal ball. Amount of heat gained by the ice = amount of heat lost by water Amount of heat gained by the water = amount of heat lost by metal ball Using principle of mixture we can measure the specific heat capacity of the solids.

18. Thermal Expansion • Three types of thermal expansion • Linear expansion. • Superficial expansion. • Volume expansion. Thermal expansion - video Thermal expansion : The expansion of a substance on heating is called thermal expansion.

19. Thermal Expansion Linear expansion Increase in length due to heating is called linear expansion. Change in length = ∆x x superficial expansion Increase in area due to heating is called superficial expansion. Change in area = = ∆ y ∆ x ∆ A ∆ X ∆ Y x ∆x

20. Thermal Expansion Volume expansion Increase in volume due to heating is called volume expansion. Initial volume = V Final Volume = V + Change in volume = ∆V ∆V Examples Linear expansion Volume expansion (video) Superficial expansion home

21. Change of state Matter exists in three states 1. solid 2. liquid and 3. gas.

22. Change of state Melting Freezing Vapourisation. The process in which a solid changes into liquid on heating is called melting. The change of a liquid into a solid on cooling is known as freezing. The process in which a liquid changes into vapour on heating is called vapourisation. example EXIT example example EXIT EXIT Ice changes into water Water changes into ice Water changes into steam Do you Know? Some materials may change directly from a solid to a gas. This is called sublimation. Example : Naphthalene,  CO2 (dry ice) EXIT Click to view Do you know?

23. Change of state Heat energy taken from the environment Sublimation MELTING Evaporation Freezing Condensation Deposition Heat energy released to the environment home

24. Latent heat If water is heated its temperature rises till it reaches 100oC.If water is heated more than 100o Cits temperature remains constant for some time. During this time it changes its phase from liquids to gas. If ice is heated its temperature rises till it reaches 0oC. If ice is heated more than 0o C its temperature remains constant for some time. During this time it changes its phase from Solid to liquid. The latent heat of a substance is defined as the amount of heat absorbed by a unit mass of the substance to change its state without Change of temperature. home

25. Cooling due to evaporation FACT FILE On a rainy day, wet clothes take longer time to dry, because large amount of vapour already present in the air, slows down the evaporation. I feel too cool Dogs keep their tongue usually out in summer. Water evaporates from the tongue and keeps it cool. EXIT Water comes out of the pores of the vessel and evaporates. Therefore water remains cool in an earthen vessel by evaporation. Click to view the fact file home

26. Working principle of refrigerator When a liquid evaporates it takes in heat energy and cools its surroundings. When the gas condenses back to a liquid, the latent heat is released. This principle is used to take heat from inside a fridge, and release it outside. By compressing gases, we make them hotter. Letting them expand, we make them cooler.

27. Working principle of refrigerator Evaporator coil (heat exchange pipe) Condenser coil = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Expansion valve (heat exchange pipe) = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Compressor = = = = = = = = = = = = = = = = home

28. Latent heat Latent heat of vapourisationof a liquid is the amount of heat required to convert unit mass of a liquid at its normal boiling point into vapour at the same temperature. The latent heat of fusion of a substance is the quantity of heat required to convert unit mass of the solid at its melting point to the liquid state at the same temperture.

29. Phase transition graph Time Vs Temperature graph F 150 100 50 0 -50 Temperature ( o C) D E Time B C A to B - pure iceB to C - a mixture of water and ice all at 0 ºCC to D - pure waterD to E - a mixture of water and steam all at 100 ºCE to F - pure steam A home

30. Self evaluation • 1. Transfer of heat in fluids is due to • Conduction b) Convection • 2. When a liquid evaporates, its temperature • a) rises b)falls C) does not change • 3. The process of changing a solid into gas directly is called • a) melting b) freezing C) sublimation • 4. Evaporation occurs at • a) the surface of the liquid b) the bottom of the liquid • c) the middle of the liquid d) both at surface and bottom of a liquid • 5. When water solidifies to ice • a) heat is absorbed b) heat is released • b) temperature increases d) ) temperature decreases • 6. The volatile liquid used in refrigerator is • a) Freon b) water • c) helium d) acetone • 7. Total amount of heat required to melt the solid is • a) H = m s T b) m s c) T s d) L T

31. Self evaluation • 1. Mercury is used as a thermometric liquid. Why ? • 2. Define specific heat capacity of a substance. • 3. Define heat capacity of a substance. • 4. Why gaps are left in bridges, railway lines and concrete highways ?

32. PRESENTED BY BERGIN .G MEDIA DOCUMENTATION OFFICER SHARVA SHIKSHA ABHIYAN KANYAKUMARI DISTRICT TAMIL NADU EMAIL : berging76@gmail.com Please visit http://berging76.edu.glogster.com/ http://scienceoftheday.blogspot.com/ http://bergin-digitalclassroom.blogspot.com/ THANK YOU Background voice by M.A.Adarshana EXCEL central school,Thiruvattar R.Ashick Rajah EXCEL central school,Thiruvattar

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