MHT CET202520 Apr 2025Morning ShiftPhysicsDual Nature of MatterActual
A parallel beam of light is incident normally on a plane surface absorbing 50 % of the light and reflecting the rest. If the incident beam carries 90 W of power, the force exerted by it on the surface is ( C = . velocity of light in air .=3 10^8 ~m / s )
Options
- A4.5 10⁻⁷ ~N
- B1.5 10⁻⁷ ~N
- C3 10⁻⁷ ~N
- D9 10⁻⁷ ~N
Correct answer
A. 4.5 10⁻⁷ ~N
Step-by-step solution
Given an incident power P = 90 W and light velocity c = 3 10^8 m/s , with 50% absorption and 50% reflection. The absorbed power is P_ abs = 0.50 90 = 45 W , and the reflected power is P_ ref = 0.50 90 = 45 W . The force due to absorbed light is F_ abs = 45 3 10^8 = 1.5 10⁻⁷ N . For reflection, the force is F_ ref = 2 45 3 10^8 = 3 10⁻⁷ N . The total force exerted is F_ total = F_ abs + F_ ref = 4.5 10⁻⁷ N . The final answer is A .