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

`P_("initial") = E/c`
`P_("final") = -E/c`
The change in momentum is the impulse, which is the momentum transferred to the surface:
`DeltaP = P_("final") - P_("initial.) = E/c -(-E/c) = (2E)/c`