A lamp is moved from 10 cm to 20 cm from a pondweed. Light intensity is inversely proportional to the distance squared. By what factor does the light intensity fall?
Answer and explanation
Correct answer: A. 4
- Step 1: Distance doubles from 10 cm to 20 cm.
- Step 2: Intensity ∝ 1/d², so the intensity falls by 2² = 4.
Answer
4.
Why not the others: 2: this ignores squaring the distance. 8: this cubes the distance. 16: this squares the factor twice.
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