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CAIE A-Level Physics 14.3 Specific Heat Capacity and Latent Heat

Practise using Q = mcΔT and Q = mL for heating and phase changes, distinguishing specific heat from latent heat and interpreting energy data.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • define and calculate specific heat capacity using ΔQ = mcΔT
  • define and calculate specific latent heat using ΔQ = ml and distinguish fusion from vaporisation
  • interpret heating, cooling and change-of-state data in energy terms

Covered syllabus points

14.3.1—Specific heat capacity14.3.2—Specific latent heat and distinguish between specific latent heat of fusion

14.3 Specific heat capacity and specific latent heat question 1

[Maximum number: 3]

A fixed mass of an ideal gas at a temperature of 20∘C20^{\circ} \mathrm{C} is sealed in a cylinder by a piston, as shown in Fig. 2.1.

Fig. 2.1

Fig. 2.1

The initial volume of the gas is 1.24×10−4 m31.24 \times 10^{-4} \mathrm{~m}^{3}.
Thermal energy is supplied to the gas and its volume increases by 5.20×10−5 m35.20 \times 10^{-5} \mathrm{~m}^{3}.

The mass of the gas is 16 g . For this expansion, there is a net transfer of 960 J of thermal energy to the gas.

Calculate the specific heat capacity c of the gas at this pressure.

c=…………………………………..Jkg−1 K−1c=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \mathrm{Jkg}^{-1} \mathrm{~K}^{-1}

14.3 Specific heat capacity and specific latent heat question 2

[Maximum number: 8]

Question (a)

(a)

State what is meant by specific latent heat.

[ 2 ]

Question (b)

(b)

A student uses the apparatus illustrated in Fig. 3.1 to determine a value for the specific latent heat of fusion of ice.

Fig. 3.1

Fig. 3.1

The balance reading measures the mass of the beaker and the melted ice (water) in the beaker.

The heater is switched on and pieces of ice at 0∘C0^{\circ} \mathrm{C} are added continuously to the funnel so that the heater is always surrounded by ice.

When water drips out of the funnel at a constant rate, the balance reading is noted at 2.0 minute intervals. After 10 minutes, the current in the heater is increased and the balance readings are taken for a further 12 minutes.

The variation with time of the balance reading is shown in Fig. 3.2.

Fig. 3.2

Fig. 3.2

The readings of the ammeter and of the voltmeter are shown in Fig. 3.3.

Fig. 3.3

Fig. 3.3

[ 6 ]

Question (i)

(i)

Determine a value for the specific latent heat of fusion L of ice.

[ 4 ]

Question (ii)

(ii)

Calculate the rate at which thermal energy is transferred from the surroundings to the ice.
rate = W

[ 2 ]
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