Text Book Physics Form 4 - Chapter 4

Chapter 4 Heat

8. Air in the tyre of a car has a pressure of 220 kPa at initial temperature of 27°C. After a
race, the temperature of the air increases to 87oC.
(a) Calculate the air pressure in the tyre after the race.
(b) What assumptions did you make in 8(a)?

9. An air bubble is trapped under a leaf floating on the water surface of a lake. The volume of
the air bubble is 3.6 cm3 when the temperature is 20°C.
(a) What is the volume of the air bubble when the water temperature rises to 38°C?
(b) State three assumptions that need to be made in your calculations in 9(a).

10. Figure 2 shows ice cubes being heated by a 500 W immersion heater for 80 seconds. The
melted ice cubes are collected in a beaker.
[Specific latent heat of fusion of ice = 3.34 × 105 J kg–1]

Power supply Immersion heater
Filter funnel
Ice
Retort stand
Beaker
Water

Figure 2

(a) What is meant by specific latent heat of fusion?
(b) Why does the temperature remain unchanged when the ice cubes are changing into

liquid?
(c) Calculate:

(i) energy absorbed by the ice cubes.
(ii) mass of melted ice cubes.
(d) What assumptions are made in your calculations in 10(c)?

11. An electric kettle is filled with 500 g of water at 30°C. The power of the heating element of
the kettle is 0.8 kW. Assume that all heat from the heating element is transferred to
the water.
[Specific heat capacity of water = 4 200 J kg–1 °C–1]
(a) Calculate:
(i) heat energy needed to increase the temperature of the water to 100°C.
(ii) time taken by the kettle to heat water to a temperature of 100°C.
(b) Why is the handle of the kettle made of plastic?
(c) Why is the heating element of the kettle made of metal?
(d) The heating element of the kettle is located at the base of the kettle. Explain why.

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12. A substance has a mass of 250 g. The substance loses 5 625 J of heat when cooled. There is
a 25°C drop in temperature.
(a) Calculate the specific heat capacity of the substance. Identify the substance based on
Table 4.2 on page 128.
(b) Explain the use of the substance based on its specific heat capacity.

13. Photograph 3 shows a bamboo steamer. Amin receives an
order from a supermarket to supply 400 steamed buns per
day. Suggest and explain the design of the steamer needed.
The steamer should be durable, and able to prepare a large
quantity of steamed buns in a short time.

Photograph 3

Enrinchment Corner

14. Khairi orders a cup of coffee in a restaurant. He finds that the coffee is too hot.
Photograph 4 shows two suggested ways to cool the coffee.

Ice

Ice

Method A Method B

Photograph 4

(a) Discuss the suitability of methods A and B to cool the coffee in the cup.
(b) State your choice. Give reasons for your choice.

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