A2 Daily A Level Physics question
Two identical electric heaters supply the same power for 4.0 minutes to equal masses (200 g) of liquids A and B in well-insulated cups, both starting at 20 °C. After 4.0 minutes, A is at 40 °C while B is at 30 °C. Which statement must be true?
Answer
The correct answer is C.
Correct: C — Liquid B’s specific heat capacity is about twice that of liquid A. A The one that warms more for the same energy has the smaller specific heat, so A’s is not larger. B Identical power for the same time means equal energy transfer, so their internal energy increases are the same, not twice. C With equal mass and energy input, specific heat is inversely proportional to temperature rise: ΔT_A/ΔT_B = 20/10 = 2, so c_B ≈ 2c_A. D The heaters are identical, so the energy per second (power) was the same; the different temperature rises reflect different specific heats.