is the heat capacity of the spoon? You may ignore other possible heat transfers.
(24)
(b) Name two processes by which a hot drink cools. How is the energy lost by each of these processes reduced for a hot drink supplied in a disposable cup?
(14)
(c) A thermocouple is used to measure the temperature of the steam. How would you demonstrate the principle of operation of a thermocouple?
Describe how to establish a calibration curve for a thermocouple. (18)
(cmilk = 3.90 × 103 J kg–1 K–1, cwater = 4.18 × 103 J kg–1 K–1, chot drink = 4.05 × 103 J kg–1 K–1, specific latent heat of vaporisation of water = 2.34 × 106 J kg–1)
2006 12. (c) Define (i) power, (ii) specific heat capacity.
Calculate:
(i) the energy required to raise the temperature of the water to 100 °C
(ii) the energy supplied by the kettle per second
(iii) the least amount of time it would take to heat the water to 100 °C.
In reality, the time taken to heat the water will be greater. Explain why.
(specific heat capacity of water = 4200 J kg–1 K–1)
2004 7. Define (i) specific heat capacity, (ii) specific latent heat.
(12)
500 g of water at a temperature of 15 °C is placed in a freezer. The freezer has a power rating of 100 W and is 80% efficient.
(i) Calculate the energy required to convert the water into ice at a temperature of –20 °C.
(ii) How much energy is removed every second from the air in the freezer?
(iii) How long will it take the water to reach a temperature of –20 °C? (27)
Allowing a liquid to evaporate in a closed pipe inside the freezer cools the air in the freezer. The vapour is then pumped through the pipe to the outside of the freezer, where it condenses again.
Explain how this process cools the air in the freezer. The freezer causes the room temperature to rise. Explain why.
(12) (5)
(specific heat capacity of ice = 2100 J kg–1 K–1; specific heat capacity of water = 4200 J kg–1 K–1; specific latent heat of fusion of ice = 3.3 × 105 J kg–1)
(15) (4) (9)
400 g of water at a temperature of 15 °C is placed in an electric kettle. The power rating of the kettle is 3.0 kW.
