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A2 Daily A Level Physics question

2026-05-03 OCR A Thermal physics I: heating curves (qual.) Module 5.2: Thermal physics — internal energy, specific heat capacity and latent heat; heating and cooling curves (qualitative)

In a school lab, a 100 W immersion heater warms 200 g of crushed ice in a well‑insulated beaker. The mixture is stirred, and a temperature probe reads close to 0 °C for several minutes while the ice slowly disappears. Which statement must be true during this time?

  1. A The internal energy of the ice–water mixture is constant because the temperature does not change.
  2. B The specific heat capacity of the mixture becomes extremely large, so energy input produces almost no temperature rise.
  3. C The heater’s electrical power is mostly lost to the surroundings, so little energy enters the mixture.
  4. D The energy supplied increases the internal potential energy by separating molecules, while the average kinetic energy (and temperature) stays roughly constant. (correct)

Answer

The correct answer is D.

Correct: D — The energy supplied increases the internal potential energy by separating molecules, while the average kinetic energy (and temperature) stays roughly constant. A The temperature is constant but internal energy increases due to latent heat absorbed during melting. B During a phase change the idea of specific heat capacity is not the relevant model; latent heat explains energy input at constant temperature. C The setup is well insulated and the persistent plateau is due to energy going into the phase change, not predominantly to losses. D This captures that energy goes into breaking/intermolecular separation while kinetic energy (hence temperature) remains about constant.

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