A2 Daily A Level Physics question
In a lab test, equal masses of copper and aluminium start at the same temperature. Each block is heated by an identical constant‑power heater for the same time in good insulation. The copper block’s temperature increases by 30°C. Using typical specific heat capacities (copper ≈ 390 J kg⁻¹ °C⁻¹, aluminium ≈ 900 J kg⁻¹ °C⁻¹), what is the approximate temperature rise of the aluminium block?
Answer
The correct answer is B.
Correct: B — 13°C. Both blocks receive the same energy and have equal mass, so the temperature rise is inversely proportional to specific heat capacity: ΔT_Al/ΔT_Cu = c_Cu/c_Al ≈ 390/900 ≈ 0.43, giving about 0.43 × 30 ≈ 13°C. A 69°C — this treats temperature rise as proportional to specific heat capacity, reversing the inverse relationship. B — correct because equal energy into equal masses means larger specific heat capacity gives a smaller temperature change in the ratio c_Cu:c_Al. C 30°C — assumes the same temperature rise for both simply because the energy input is the same, ignoring the different specific heat capacities. D 7°C — roughly half the correct value, as if the (equal) masses had been double-counted; the mass cancels when comparing the two blocks.