A2 Daily A Level Physics question
Two identical insulated beakers are each heated by the same 100 W immersion heater for 60 s, with stirring. Beaker X contains 0.10 kg of ice at −5°C. Beaker Y contains 0.10 kg of liquid water at +5°C. Which statement must be true immediately after the heating?
Answer
The correct answer is B.
Correct: B — Y warms by about 14°C, while X is held at 0°C with ice still present. A ignores that temperature rise depends on specific heat and phase changes; same 6000 J gives different ΔT, and in X most energy is used without raising temperature beyond 0°C. B is correct because Y’s rise is ΔT ≈ 6000 J ÷ (0.10 kg × 4200 J kg⁻¹ K⁻¹) ≈ 14°C, whereas X uses 0.10×2100×5 ≈ 1050 J to reach 0°C and the remaining 4950 J goes into melting (latent heat), keeping it at 0°C. C reverses the outcome by focusing only on lower specific heat of ice and neglecting the large latent heat needed to melt it. D is wrong because 6000 J is sufficient to raise 0.10 kg of liquid water by over 10°C, not leave it “near 0°C.”