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Understanding Heat: Conduction, Convection, and Radiation

Learn about heat as a form of energy, conductors vs. insulators, temperature measurements, changes of state, and methods of heat transfer in this comprehensive unit.

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Understanding Heat: Conduction, Convection, and Radiation

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  1. At the end of this unit you should: 1. Be able to show that heat is a form of energy and that it can be converted into other forms of energy. 2. Be able to identify good and bad conductors of heat and compare the insulating ability of different materials. 3. Be able to describe the difference between an insulator and a conductor. 4. Know how to investigate and explain why matter expands when heated and contracts when cooled. 5. Be able to explain why water expands on freezing.

  2. At the end of this unit you should: 6. Be able to measure the temperature of various solids and liquids at, above and below room temperature. 7. Understand the difference between heat and temperature. 8. Know how to carry out experiments that involve changes of state from: • solid to liquid and liquid to solid • liquid to gas and gas to liquid. 9. Be able to plot a cooling curve/heating curve and use latent heat to explain the shape of the curve.

  3. bimetallic strip conduction conductor convection convection current energy expansion heat insulator joules latent heat radiation specific heat capacity temperature thermometer vacuum

  4. LIGHTBULB QUESTION Fire, warm, heating things up, cooking, temperature or objects being hot.

  5. Heat: A form of energy. Unit: the joule (J).

  6. (a) Looking at Fig. 11.02.01, can you list the objects where you think heat is being given out. • Radiator, TV, fireplace, wall lamps.

  7. (b) Suggest a reason as to why you feel the heat from a fire in a room. • Heat has energy and it is the energy we can feel.

  8. Conduction: The transfer of heat energy through a solid by the vibration of particles.

  9. (a) Define heat. • Heat is a form of energy. (b) What is the unit of heat? • The unit of heat energy is the joule (J). (c) Complete the sentence, ‘Heat is a form of_______’. • energy

  10. (d) Why, when we put a poker into a fire, does the poker burn our hands? • It is made of a metal, which is a poor conductor or heat.

  11. Investigation 11.02.01: Good and bad conductors Equipment: Wax, some metal rods (copper, aluminium, brass, nickel and steel), some identical nails, Bunsen burner, tripod, drawing pin and wire gauze.

  12. Investigation 11.02.01: Good and bad conductors Instructions: 1. Align all rods so that at one end, the rods are touching, with the other ends spread away from each other. 2. Place some Vaseline or wax at the spread end of the rod and attach a drawing pin to each, facing down. 3. Now place the Bunsen burner under the end of the rods that are touching and heat up the rods. 4. Take note of which drawing pins drop first.

  13. 1. Compare which metal was the best conductor and which was the worst. • This depends on the metals you use. If copper is used, it will be the first to see the nail/drawing pin fall off. • 2. How did you ensure this was a fair test? • Same length and thickness was kept for all the metals. All were heated evenly and the same amount of wax was used for each nail/drawing pin. • 3. What other substances could you have used instead of wax? • Parafilm, Vaseline or any other suitable substitute.

  14. Conductor: Allows heat energy to transfer through it easily.

  15. Insulator: Does not allow heat energy to transfer through it easily.

  16. Convection: The transfer of heat through a liquid or gas.

  17. LIGHTBULB QUESTION Warm air rises. Birds can use this effect to glide/hover in the air, conserving their energy while looking for prey. This use of convection currents is most commonly seen in eagles.

  18. (a) Put your hand over a warm radiator. What do you feel? That heat rises from the radiator. (b) Where does the steam come from when a kettle of water boils? The steam comes from the boiling of water inside the kettle.

  19. DEMONSTRATION Demonstration 11.02.01 – Showing a convection current Equipment: Spatula-tip of potassium permanganate crystals, water, beaker, tripod stand, wire gauze, Bunsen burner/hot plate.

  20. DEMONSTRATION Instructions: 1. Fill a beaker with water. 2. Gently place some potassium permanganate crystals into the bottom left of the beaker. 3. Allow some time for the crystals to settle. 4. Heat the bottom of the beaker where you have placed the crystals. 5. Watch as the convection currents form.

  21. Vacuum: A region of space where all atoms have been removed. Radiation: The transfer of heat energy from a hot object without particles.

  22. LIGHTBULB QUESTION White-coloured clothing reflects the heat, dark-coloured clothing absorbs the heat. So by that logic one should wear light-coloured clothing in the summer and dark colours in the winter. However, people who live in desert areas generally wear black, loose-fitting clothing. This is because the black absorbs the light, preventing it from reaching the skin. As the fabric heats up, the hot air rises, with cold air rising up from the feet, effectively creating a fan inside the robe. So the answer isn’t as black and white as it seems!

  23. How many methods of heat transfer are there? Name these methods. Three: Conduction, convection and radiation. (b) ‘All metals are good conductors of heat.’ Give your own opinion on this statement and back it up with evidence. All metals can conduct heat. However, some of them are not good conductors. For example, the metal used in a fire poker is an example of an insulator; if it were a good conductor of heat, it would burn the hand of the user.

  24. (c) ‘If you want to heat up your house, your radiators should be made of insulating material.’ State your opinion on this theory and give evidence for your opinion. If radiators were made of insulating material, they would not allow the heat to escape. This is why radiators are made of aluminium. The standard hot-water radiator works via convection.

  25. Investigation 11.02.02: The heating effect on a metal Equipment: Ball and ring apparatus, Bunsen burner.

  26. Investigation 11.02.02: The heating effect on a metal Instructions: 1. Using the ball and ring apparatus, try to place the ball through the ring and note what happens. 2. Heat the ball using the Bunsen burner. 3. Try to place the ball through the ring and note what happens.

  27. 1. What did you observe in your investigation? • When cool, the ball would fit through the ring. When the ball was heated it no longer fitted through the ring. • 2. What would you need to do if you wanted to repeat this investigation multiple times? • The ball would need to be cooled back to room temperature. This can be achieved by putting it in water. • 3. What safety precautions did you take when conducting this investigation? • Heat-resistant gloves were worn when heating and handling the ball and ring apparatus. Full PPE was also worn.

  28. Explain how a bimetallic strip works and name the two metals used. Two metals, usually iron and copper, are welded together. Copper will conduct heat energy faster than iron and therefore expand more. This expansion causes the strip to bend a certain way, depending on where the copper is placed.

  29. Temperature: The measure of how hot or cold an object is.

  30. LIGHTBULB QUESTION Getting burnt by steam at 100˚C is worse than getting burnt by water at 100˚C. This is because the steam has more energy in it due to the latent heat. Therefore, the gas (steam) must first change its state from gas to liquid at 100˚C. Then the liquid needs to cool down. Water at 100˚C can start to cool down straight away as there is no change in state.

  31. Specific Heat Capacity: The amount of energy needed to change the temperature of a 1 kg substance by 1oC. Latent Heat: The heat energy required to change a substance from one state to another without a change in temperature.

  32. Investigation 11.02.03: The effects of heat on ice Equipment: Bunsen burner/hot plate, ice cubes, beaker, tripod, wire gauze and thermometer.

  33. Investigation 11.02.03: The effects of heat on ice Instructions: 1. Set up the equipment as shown. 2. Take the ice out of the freezer and dry it by patting it lightly with laboratory paper, and then crush it slightly. 3. Place the ice into a beaker along with a thermometer. 4. Allow the ice to melt and take measurements of the temperature every 1–2 minutes. 5. Once the ice has melted, allow additional time for the temperature to settle above 0 degrees. 6. Now heat the beaker up using a Bunsen burner. Take note of the temperature every minute. 7. Continue to take measurements until most of the water has been evaporated.

  34. 1. How did you ensure this was a fair test? • By ensuring the ice was dry, the water was stirred throughout the experiment and measurements were taken at regular intervals. • 2. Is your graph similar to Fig. 11.02.11? If so, tell the story of this graph. If not, explain the story of your graph and suggest possible reasons why your graph is different. • Possible reasons for difference in graphs: water was not stirred between measurements; not enough time given between changes in state.

  35. 3. Does your graph show latent heat? Justify your answer. • Graph should show a horizontal line at 0 and 100 degrees as this is the change in state with no change in temperature. • Example:

  36. Copy and Complete In this unit I learned that heat is a form of energy. There are threemethods for heat transfer. Conduction is the transfer of heat through a solid via the vibration of molecules. Convection is transfer of heat through a liquid via the movement of particles through a convectioncurrent. Radiation is the transfer of heat through a vacuum via electromagnetic radiation. If an object allows heat to pass through it easily it is called a conductor. If it does not allow heat to pass through it easily it is called an insulator. When heated, solids, liquids and gases all expand. Similarly when cooled, solids, liquidand gases all contract. Temperature is the measure of how hot or colda body is. I must remember that temperature is not the same as heat.

  37. 1. Explain temperature. The degree of heat present in a substance or object. 2. Distinguish between temperature and heat. Heat is a form of energy. Temperature is the measure of how hot or cold an object/substance is. 3. Define latent heat. The heat energy required to change a substance from one state to another without a change in temperature. 4. What are the four states of matter? Solid, liquid, gas and plasma.

  38. 5. Using diagrams to justify your explanation, describe how much energy particles have in the three states of matter.

  39. 6. Describe how to calibrate an alcohol thermometer. To calibrate a thermometer (mark it with a standard scale to read it), we only need two measurements: 100˚C and 0˚C, both of which are easy to determine. When a thermometer is made, it is placed in boiling water. This is because water boils at 100˚C. A mark is made when the liquid reaches its reading for this temperature. Next the water is placed in ice water because ice water is 0˚C. This point is also marked. Then, marks are made at intervals of 1˚C.

  40. 7. Latent heat changes the state of the substance without changing the temperature. Using your knowledge of bonding, can you suggest the reason why there is no increase in temperature? Take ice for example. Ice is solid water. This means the particles are all compact and tight together. As we pump energy into the ice, it begins to melt. This is due to the particles gaining energy and their vibrations intensifying. Once we hit the latent heat phase of this process, all the energy being pumped into the molecules is actually being used to break these bonds, i.e. free the molecules from the solid, so no energy is being given to increase its temperature. Once all the molecules are free, they become a liquid and the heat energy is now used to increase the temperature of the molecules.

  41. 8. Peter is working on repairs to an old house. He has left a bottle of water, some metal nails and a piece of timber inside the boot of his car. After the car has been out in the sun for three hours, the temperature inside the car reaches about 40oC. What happens to the objects in the car? Copy and complete Table 11.02.01 by answering ‘Yes’ or ‘No’ for each statement, and give your reasons.

  42. 8. Peter is working on repairs to an old house. He has left a bottle of water, some metal nails and a piece of timber inside the boot of his car. After the car has been out in the sun for three hours, the temperature inside the car reaches about 40oC. What happens to the objects in the car? Copy and complete Table 11.02.01 by answering ‘Yes’ or ‘No’ for each statement, and give your reasons.

  43. 9. Table 11.02.02 shows the data collected for the cooling curve of chocolate. (i) Draw the cooling curve for the data contained in Table 11.02.02.

  44. (i) Draw the cooling curve for the data contained in Table 11.02.02.

  45. (ii) Which state of matter describes the chocolate when it is at 30˚C? Liquid.

  46. (iii) Which state of matter describes the chocolate when it is at 10˚C? Solid.

  47. (iv) In terms of heat loss or heat gain, describe and explain what happens to the chocolate between position A and position B in Fig. 11.02.12. (2014 JC HL) The distance between these points represent latent heat, so no change in temperature occurs but a change in state occurs.

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