A 450 W isotropic light source illuminates a perfectly reflecting surface placed 2 m away. The radiation pressure on the surface is:
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Question

A 450 W isotropic light source illuminates a perfectly reflecting surface placed 2 m away. The radiation pressure on the surface is:

G1 Physics · Accepted Answer

For an isotropic source, intensity at distance r is I = P/(4πr²). For a perfectly reflecting surface at normal incidence, radiation pressure is p = 2I/c. Therefore, p = 2P/(4πr²c). Substitute P = 450 W, r = 2 m, c = 3×10⁸ m/s. Using π ≈ 22/7, p ≈ 6×10⁻⁸ Pa. Correct option: B.