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A2 Daily A Level Physics question

2026-02-02 OCR A Thermal Physics & Gases (M5) OCR-A Module 5.1 Thermal physics — specific heat capacity (5.1) OCR-A Practical skills: energy transfer by electrical heating; data handling with ratios

Two identical immersion heaters run at the same power for the same time. One heats 0.50 kg of cooking oil from 20 °C to 50 °C, while the other heats 0.80 kg of water from 20 °C to 32 °C. Assuming negligible losses and identical containers, what is the ratio of the specific heat capacities c_water : c_oil?

  1. A Approximately 0.64 (water lower than oil)
  2. B Approximately 2.5 (ignoring mass differences)
  3. C Approximately 1.6 (water higher than oil) (correct)
  4. D Approximately 1.0 (about the same)

Answer

The correct answer is C.

Correct: C — Approximately 1.6 (water higher than oil). With equal electrical energy supplied, c ∝ 1/(mΔT), so c_water/c_oil = (m_oil × ΔT_oil)/(m_water × ΔT_water) = (0.50×30)/(0.80×12) ≈ 15/9.6 ≈ 1.56 ≈ 1.6. A This is the inverse (9.6/15), from swapping the ratio. B This uses only the temperature rises (30/12 ≈ 2.5) and ignores the different masses. C Uses both mass and temperature change correctly to compare how much energy per kilogram per degree each substance needs. D Equal energy input does not imply equal specific heat capacity when masses and temperature changes differ.

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