Calculate the momentum transferred to a surface when a radiation of energy E falls normally on it. Assume that the reflectivity of the surface is unity.

Options

A. `E//c`
B. `2E//c`
C. `Ec`
D. `E//c^(2)`

Answer

B

Explanation

Since the photons incident normally and reflectivity isone. Therefore the photons turn is `180^(@)` after collision with the surface.
Energy of a photons given is E.
Then initial momentum `p_(1)=E//c`
Since it is turnig back with `180^(@)` then final momentum `p_(2)=-E//c`
`:.` Change of momentum
`=p_(2)-p_(1)=(-E/c)-(E/c)=-(2E)/c`
`:.` Momentum transferred to surface
`=(2E)/c`