Physicshard · Past Paper
A point source of light is placed at the bottom of a tank of water (n=4/3) of depth 1m. The area of the surface of water through which light can emerge is:
Aπ / 0.75
B9π / 7
Cπ / 3
D3π / 4
✓ Correct Answer: B — 9π / 7
Radius r = h / sqrt(n^2 - 1). r = 1 / sqrt(16/9 - 1) = 1 / sqrt(7/9) = 3/sqrt(7). Area = πr^2 = 9π/7.
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