Question

A light source of power 50watt emitting a light of wavelength 5000A° which incident on a surface normally.the surface behaves as 50%perfectly reflecting surface. Find the force exerted on the surface
a) 25×10-6n. b) 25×10-9n c) 15×10-8 d) 25× 10-8n

Answer 1

Wavelength of incident light (λ) = 5000Å = 5000 x 10-10 m
Speed of light (c) = 3 x 108 m/s
V=c/ λ
  = 3 x 108/5000 x 10-10
  = 6 x 1014 Hz
The wavelength and frequency of incident light is the same as that of reflected ray. Hence, the wavelength of reflected light is 5000Å and its frequency is 6 x 1014 Hz.
According to the law of reflection, The angle of incidence + angle of reflection = 90°
The angle of incidence (i) = 90/2 = 45°
Therefore, the angle of incidence for the given condition is 45°.