Image. A plate of mass 20 g is held in equilibrium in air by a light beam as shown. The plate is perfectly absorbing. Find the beam power.
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Image. A plate of mass 20 g is held in equilibrium in air by a light beam as shown. The plate is perfectly absorbing. Find the beam power.

G1 Physics · Accepted Answer

For complete absorption, radiation pressure force is F = P/c. Equilibrium requires P/c = mg. With m = 0.020 kg, g ≈ 10 m s⁻² and c = 3 × 10⁸ m s⁻¹, P = mgc = 6 × 10⁷ W. Correct answer: C.