1. 1 1.2 Heat and internal energy Hand warmer and cooling belt Heat Internal energy Power Check-point 2 1.2Heat and internal energy ?

2. 2 Have you ever used hand warmers in cold weather? Hand warmer and cooling belt Why can it warm you up?

3. 3 1.2 Heat and internal energy Hand warmer and cooling belt Have you ever used cooling belts when you have a fever? Why can it cool you down?

4. 4 1.2 Heat and internal energy 1Heat When two bodies of different temperatures touch each other, body of lower temp.  warmed up body of higher temp.  cooled down

5. 5 1.2 Heat and internal energy Energy is transferred between bodies of different temperatures until they reach the same temp. Such energy transferred is called heat. Heat A form of energy Unit: Joule (J) 1Heat

6. 6 1.2 Heat and internal energy In doing work, such as drilling a wood, chemical energy in our body  internal energy of the wood Energy is transferred from one body to another. 1Heat

7. 7 1.2 Heat and internal energy 2Internal energy aWhat is internal energy? Energy stored in a body Internal energy  when... –temp. of the body  ; –the body changes state: solid  liquid/liquid  gas Unit: Joule (J)

8. 8 1.2 Heat and internal energy bTemperature and internal energy E internal energy kinetic energy (KE) potential energy (PE) = + T ,  particles move faster  ave. KE  T ,  particles move faster  ave. KE  Solid  liquid/ Liquid  gas  particles further apart  PE  Solid  liquid/ Liquid  gas  particles further apart  PE 

9. 9 1.2 Heat and internal energy 3Power Unit: watt (W) / joule per second (J s –1 ) How long does it take to heat up an object or how fast is the work done?  rate of energy transfer

10. 10 1.2 Heat and internal energy 3Power Energy transferred = 1 kilowatt-hour (kW h) = 3.6 MJ = 1000 W  60  60 s unit for calculating the cost of electricity When 1-kW heater is switched on for 1 h...

11. 11 1.2 Heat and internal energy Joulemeter measures the energy supplied to low voltage (12 V a.c.) appliances 3Power Kilowatt-hour meter measures the energy supplied to appliances connected to the mains (220 V a.c.)

12. 12 1.2 Heat and internal energy 1When we put a spoon…When we put a spoon… 2Which of the following statements...Which of the following statements... 3A light bulb is connected to...A light bulb is connected to... 4What is the energy consumed...What is the energy consumed... 5An immersion heater rated at…An immersion heater rated at… Check-point 2 E

13. 13 1.2 Heat and internal energy Check-point 2 – Q1 When we put a spoon into a bowl of hot soup,

14. 14 1.2 Heat and internal energy Check-point 2 – Q1 Athe internal energy of the soup is transferred to the spoon. Bthe internal energy of the soup decreases. Cthe spoon stores more heat. Dthe temperature of the spoon falls.

15. 15 1.2 Heat and internal energy (1)Heat (2)Internal energy Check-point 2 – Q2 A(1) only. B(2) only. C(1) and (2) only. D(1), (2) and (3). Which of the following physical quantities is/are measured in joule? (3)Power

16. 16 1.2 Heat and internal energy Check-point 2 – Q3 A light bulb is connected to a joulemeter. The light bulb is on and the reading of the joulemeter 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. E

17. 17 1.2 Heat and internal energy Check-point 2 – Q4 What is the energy consumed by a 2-kW heater in 30 minutes? Energy consumed by the heater = Pt= 2000 × 30 × 60 = 3 600 000 J = 3.6 MJ

18. 18 1.2 Heat and internal energy 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? E P 15 000 50 300 s

19. 19 1.2 Heat and internal energy The End

20. 20 1.2 Heat and internal energy Example 2 A 1-kW heater is put in water and switched on for 1 h. How much energy is transferred to the water? Energy transferred E = Pt = 1000 × 3600 = 3 600 000 J = 3.6 MJ

21. 21 1.2 Heat and internal energy Return