A2 Daily A Level Physics question
In a lab, a pure solid in an insulated beaker is heated at constant power. The heating curve shows a flat plateau at its melting point that lasts 6.0 minutes with a 50 W heater. If the same setup is repeated with a 100 W heater, which statement about the duration of the melting plateau must be true?
Answer
The correct answer is B.
Correct: B — It halves compared with the 50 W run. The energy needed to melt the sample is fixed; doubling the power doubles energy per second, so time = energy/power halves (e.g. 6.0 min becomes 3.0 min). A says doubles, which reverses the effect of increased power. B is correct as explained. C ignores that a higher power delivers the same required energy in less time. D suggests a quarter of the time, which would require four times the power, not twice.