Question

Parallel beam of light is incident normally on a plane surface absorbing 40% of light and reflecting the rest. If the incident beam carries 60 W power then the force exerted by it on the surface will be

Answer 1

Answer:

MEDIUM

Help best friend

Study later

ANSWER

Momentum of a photon is given as,

ρ=E/c

Momentum of the incident photons per second is,

ρ

i

=Power/c=60/3×10

8

=20×10

−8

As power of reflected light is 60% of 60W=36W, Momentum of the reflected photons per second is,

ρ

r

=36/3×10

8

=12×10

−8

, in the opposite direction to ρ

i

Force exerted by it on the surface is equal to change in momentum per second.

Force, F=ρ

i

−(−ρ

r

)=32×10

−8

=3.2×10

−7

please follow me