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AS Daily A Level Physics question

2025-12-02 OCR A Work, energy & power (M3.3) 3.3.3(a)

Two electric kettles are identical except for their power ratings: one is 1.5 kW and the other is 2.0 kW. Both heat the same mass of water from the same starting temperature to boiling with negligible heat loss. Compared with the 1.5 kW kettle, the time taken by the 2.0 kW kettle is:

  1. A about 25% less time (correct)
  2. B about 33% less time
  3. C about 25% more time
  4. D about 33% more time

Answer

The correct answer is A.

Correct: A — about 25% less time. A uses inverse proportionality (t ∝ 1/P): t2/t1 = 1.5/2.0 = 0.75, so 25% less. B assumes time falls by the same 33% as the power rise, but time varies inversely with power, not in the same direction. C wrongly suggests a higher power takes longer; it should be shorter. D is incorrect in both the direction (it should be less time) and the magnitude.

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