A Levels Physics (9702)•9702/13/M/J/25
Explanation
Efficiency in Electric Motors Steps:
- Efficiency is the ratio of useful output power to input power, expressed as a percentage.
- Formula: Output power = (efficiency × input power) / 100.
- Input power = 1 kW, efficiency = 53%.
- Output power = (53 × 1) / 100 = 0.53 kW.
Why A is correct:
- Directly applies the efficiency formula: output = input × (efficiency/100).
Why the others are wrong:
- B: Assumes 90% efficiency, not 53%.
- C: Approximates input divided by efficiency (1/0.53 ≈ 1.89 kW), which is total power needed for 1 kW output.
- D: Unrelated; far exceeds input power, violating energy conservation.
Final answer: A
Topic: Potential difference and power
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