A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is 3×108 ms

Engineering

Physics

Radiation Pressure due to Photon

Question

A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is 3×10⁸ ms^–1. The final momentum of the object is

9.0 × 10^–17 kg ms^–1

1.0 × 10^–17 kg ms^–1

3.0 × 10^–17 kg ms^–1

0.3 × 10^–17 kg ms^–1

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$P = \frac{hc}{λc} = mV = \frac{Et}{ct} = \frac{pt}{c}$

$= \frac{30 \times 10^{- 3} \times 100 \times 10^{- 9}}{3 \times 10^{8}} = 10^{- 17}$