Question

A pulse of light of duration 10^-6 s is absorbed completely by a small object initially at rest. If the power of the pulse is 60 x 10^-3 W, calculate the final momentum of the object.

Answer 1

Duration of the absorption of light pulse, t = 10^-6s

Power of the pulse P = 60 x 10^-3 W

Final momentum of the object, P = ${\displaystyle \frac{\text{U}}{\text{c}}}$

Velocity of light, C = 3 x 10⁸

Energy U = power x time

Momentum, P = ${\displaystyle \frac{60\times {10}^{-3}\times {10}^{-6}}{3\times {10}^8}}$

P = 20 × 10^-17 kg m s^-1