<p> St. Anthony's Canossian Secondary School Sec 3E Science (Physics) Chapter 9 Transfer of Thermal Energy Name: ______( ) Class: Sec ______Date: ______</p><p>Candidates should be able to: (a) show understanding that thermal energy is transferred from a region of higher temperature to a region of lower temperature (b) describe, in molecular terms, how energy transfer occurs in solids (c) describe, in terms of density changes, convection in fluids (d) explain that energy transfer of a body by radiation does not require a material medium (e) explain that the factors that affect the rate of thermal energy transferred by rafiation include: (i) colour and texture of the surface (ii) surface temperature (iii) surface area (f) apply the concept of thermal energy transfer to everyday applications</p><p>CONDUCTION</p><p>1. What is heat? Heat is a form of ______which flows from a region of ______temperature to a region of ______temperature.</p><p>2. How is heat transferred from a region of higher temperature to lower temperature? Heat can be transferred in THREE ways: a. Conduction b. Convection c. Radiation - Takes place mainly in - Takes place mainly in Can take place in solid, ______and ______liquid, gas and also - Slowly in ______- ______</p><p>3. How do we explain conduction in molecular terms? </p><p>When one end of the rod is heated, 1</p><p> The solid particles gain ______and ______faster.  As they vibrate more vigorously, they ______with their less energetic neighbouring particles and transfer some of their energy to them. The process continues until the end of the rod is heated.  In this way, heat is conducted from the ______end to the______end. </p><p>4. What is the definition of conduction? Conduction is the transfer of heat in which energy from the particles in the warmer region is passed on to the particles in the cooler region without ______of the medium (solid). </p><p>5. Do different materials conduct heat differently? Materials which allow heat to flow through it quickly are called ______. Materials which do not allow heat to flow through quickly are called ______. </p><p>Good conductors  Poor conductors  Worst conductor Solid Liquid, Gas Vacuum</p><p>Metal Non metals</p><p>6. Why are solids better heat conductors than gases? The particles in solids are ______than those in gases. The ______of the particles is therefore passed on to neighbouring particles faster in solids than in gases. Hence solids are better heat conductors than gases.</p><p>7. Why are metals good conductors of heat? Metals have vibrating atoms and ______. When these free electrons gain ______, they ______around faster and ______more with neighbouring electrons and atoms.They help to pass on the energy more quickly than vibrating atoms.</p><p>Applications of heat conduction 8. What are some applications in which heat conduction is increased? </p><p>2</p><p>Pots, pans and base of electric irons are made of ______to transfer heat quickly by conduction. However, their ladles are made of heat ______such as plastic or wood. </p><p>9. What are some applications in which heat conduction is reduced? Good ______reduce heat transfer by conduction. For example, Styrofoam cup Able to keep a drink hot for a long time because Styrofoam is a good ______, and it ______heat transfer from the hot drink to the surroundings. Cork mat The cork mat is a good ______and it reduces heat transfer from the hot coffee to the table by conduction.</p><p>Fibre glass Fibreglass is used as an insulating material in ______to reduce heat loss during winter and heat gain during summer. </p><p>10. Why do people wear wollen clothings to keep themselves warm? Wool traps air and ______is a good insulator of heat. Hence it reduces the transfer of heat from our body to the surroundings by conduction. Fur and feathers of animals trap air and ______. </p><p>CHECKPOINT</p><p>1. Explain why a saucepan has a body usually made of copper.</p><p>2. Explain why a saucepan has a handle usually made of plastic?</p><p>3. The diagram shows a styrofoam box. ICE BOX styrofoam 3</p><p>Explain why Styrofoam is used instead of metal and how the Styrofoam box helps to prevent a block of ice placed inside it from melting..</p><p>CONVECTION</p><p>10. How does water in a kettle get evenly heated when it is heated at the bottom?</p><p> When water at the bottom of a pot gains ______, it ______, becomes ______and ______to the top.  The cooler water at the top is denser and hence ______to the bottom.  The cooler water is heated by the heat source when it reaches the bottom and it rises again. .  The cycle continues and this circulation of water is called ______. It enables heat to be transferred rapidly from the bottom to the top of a fluid.</p><p>11. Definition of convection Convection is the transfer of heat by the ______of currents from one region to another in a ______or a ______.</p><p> flask 12. How to draw convection currents?</p><p> water</p><p> potassium manganate (VII) crystals</p><p> small flame</p><p>13. Why are air conditioners positioned near the ceiling of a room? 4</p><p> Cold air, which is ______, sinks.  Warm air which is ______, rises to be cooled by the air conditioner.  Cycle repeats until the room is evenly cooled. (The same concept is applied in a refrigerator where the cooling unit is placed at the top)</p><p>Think! What happens if the air-con is placed near the floor?</p><p>______</p><p>14. Natural ventilation at home Look around your class, locate the ventilation outlets in the class. Explain why they are placed in those positions ______</p><p>Checkpoint 2</p><p>1. The diagram shows some rice being boiled in a pan.</p><p> boiling water plastic aluminium rice handle pan</p><p> heat (a) Name the process by which heat passes through the bottom of the pan.</p><p>(b) Name the process that heats up the water evenly.</p><p>(c) Explain how the water at the top of the pan gets hot.</p><p>RADIATION</p><p>16. What is radiation?</p><p>5</p><p>Radiation is the transfer of heat by a component of the ______waves known as ______radiation. All objects emits radiation. The hotter the object, the ______the amount of energy radiated</p><p>17. What’s so special about radiation? Radiation is the only thermal energy transfer method that does not require a medium, it can take place in a ______. Radiation is the process which transfers the sun’s heat to us on earth because conduction and convection cannot travel through the layer of vacuum that is between the sun and the earth. </p><p>18. Why can’t conduction and convection take place in a vacuum?</p><p>19. How fast an object radiate heat depends on: 1. ______</p><p>2. ______</p><p>3. ______</p><p>4. ______</p><p> The hotter the object,  Black, dull surfaces are good  The greater the surface the ______energy ______and area, the ______it radiates per unit time. ______of thermal energy. energy it radiates per  Silver, smooth surfaces are poor unit time. ______and ______of thermal energy.  Silver surfaces are also good ______of thermal energy.</p><p>20. A black and white container of the same size and material both contains hot water.</p><p>6</p><p>The water in which container will be at a higher temperature after a few minutes? Explain your answer. </p><p>21. A black and white container of the same size and material both contains ice. The ice in which container will melt first? Explain your answer. </p><p>22. Explain why tanks that are used to store flammable liquids are highly polished and silver in colour?</p><p>23. Suggest a suitable colour for the solar heating panels be. Explain your answer? </p><p>24. Why are the cooling fins of the refrigerators painted dull black?</p><p>25. What is a suitable material, colour and texture for a teapot if it is used to keep hot tea warm for a long period of time?</p><p>26. When you place your hand at the top and at the side of the camp fire, will there be a difference in temperature? Explain your answer. </p><p>7</p><p>Vacuum Flask A vacuum flask is designed to keep hot liquids hot, and cold liquids cold. Transfer of thermal energy is ______by conduction, convection and radiation. </p><p>The plastic cap reduce heat transfer via ______because ______. It stops ______and ______. </p><p>Vacuum reduce heat transfer via ______and ______because ______</p><p>The inner silvered surface reduce heat transfer via ______because ______</p><p>The outer silvered surface reduce heat transfer via ______because ______</p><p>The foam plastic reduce heat transfer via ______because ______</p><p>8 </p>