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CAIE A-Level Physics 14.3.2 Specific Latent Heat

Practise defining specific latent heat, distinguishing fusion from vaporisation and using delta Q = ml for constant-temperature phase changes.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • define specific latent heat as energy required per unit mass for a change of state
  • distinguish specific latent heat of fusion from vaporisation and identify the relevant phase change
  • calculate energy, mass or specific latent heat using ΔQ = ml and interpret a heating or change-of-state process

14.3.2—Specific latent heat and distinguish between specific latent heat of fusion question 1

[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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