1. P.1 Book 1 Section 2.2 Heat and energy transfer Hot spring Heat Power Check-point 2 2.2Heat and energy transfer

2. P.2 Book 1 Section 2.2 Heat and energy transfer Hot spring Wow! It’s so comfortable! I feel much warmer in a hot spring. Hot spring can warm us up. Why can’t a pool of cold water do so? Energy transfer?

3. P.3 Book 1 Section 2.2 Heat and energy transfer How does energy flow between two bodies? Is that related to the temperatures of the two bodies? Hot spring

4. P.4 Book 1 Section 2.2 Heat and energy transfer 1 Heat A glass of hot tea in a cold water bath: Hot tea: Cold water: Temp , Temp , Internal energy  Internal energy  thermometers glass hot tea cold water bath

5. P.5 Book 1 Section 2.2 Heat and energy transfer 1 Heat Heat is the energy transferred from one body to another as a result of a temperature difference. Symbol: Q, unit: joule Energy can be transferred by heating or doing work.

6. P.6 Book 1 Section 2.2 Heat and energy transfer 2 Power Power= Energy transferred Time Q t P = Unit: watt (W) 1 W = 1 J s -1 Larger units of power:  kilowatt (kW) = 10 3 W  megawatt (MW) = 10 6 W

7. P.7 Book 1 Section 2.2 Heat and energy transfer 2 Power Example 1 Energy transferred

8. P.8 Book 1 Section 2.2 Heat and energy transfer Example 1 Energy transferred A 2-kW electric kettle is switched on for 1 h. Energy transferred = ? = Pt = 2000  3600 = 7 200 000 J = 7.2 MJ Energy transferred Q

9. P.9 Book 1 Section 2.2 Heat and energy transfer 2 Power kilowatt-hour (kW h): unit for calculating the cost of electricity amount of electrical energy used by a 1-kW electrical appliance in 1 h 1 kW h = (1000 J s -1 )(3600 s) = 3 600 000 J = 3.6  10 6 J

10. P.10 Book 1 Section 2.2 Heat and energy transfer 2 Power joulemeter kilowatt-hour meter Measure the energy supplied to electrical appliances Choice of meters depends on the amount of energy to be measured

11. P.11 Book 1 Section 2.2 Heat and energy transfer Check-point 2 – Q1 A light bulb is connected to a joulemeter. The light bulb is on and the joulemeter reading changes. What does the joulemeter measure? AHeat given off by the light bulb BInternal energy of the light bulb CTemperature of the light bulb DEnergy used by the light bulb

12. P.12 Book 1 Section 2.2 Heat and energy transfer Check-point 2 – Q2 When some ice is put in water, what is transferred from the water to the ice? A Heat B Temperature C Internal energy D Power

13. P.13 Book 1 Section 2.2 Heat and energy transfer Check-point 2 – Q3 A kettle transfers 540 000 J of energy to boil some water in 5 mins. Its power = A 1080 W B 1800 W C 9000 W D 108 000 W

14. P.14 Book 1 Section 2.2 Heat and energy transfer Check-point 2 – Q4 What is the energy consumed by a 2-kW heater in 30 mins? Energy consumed by the heater = Pt = 2000  60  30 = 3 600 000 J = 3.6 MJ

15. P.15 Book 1 Section 2.2 Heat and energy transfer Check-point 2 – Q5 An immersion heater rated at 50 W heats water in a polystyrene cup. How long does it take to transfer 15 000 J of energy to the water? By P =, Q t t = 15 000 50 = 300 s = 5 mins

16. P.16 Book 1 Section 2.2 Heat and energy transfer The End