An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following are true ?

Options

A. Radiation pressure is `(I)/(c )` if the wave is totally absorbed.
B. Radiation pressure is `(I)/(c )` if the wave is totally reflected.
C. Radiation pressure is `(2I)/(c )` if the wave is totally reflected.
D. Radiation pressure is in the range `(I)/(c )lt p lt (2I)/(c )` for real surfaces.

Answer

A, C, D

Explanation

Radiation pressure (P) is force applied by electromagnetic wave on unit area that is change in momentum on unit area.
Change in momentum per unit area in unit time,
`P=("Intensity")/("Wave speed")=(I)/(c )`
Change in momentum per unit area per unit time.
`Delta p =(Delta I)/(c )` (Radiation pressure p)
Change in momentum per uunit time per unit area `=(I)/(c )`
When wave is completely absorbed by surface then momentum of reflected wave in unit time per unit area = 0 (zero)
Radiation pressure,
P = Change in momentum per unit area per unit time
`=(Delta I)/(c )=(I)/(c )-0=(I)/(c )`
When wave is completely reflected then momentum of wave per unit area per unit time `=-(I)/(c )`
`therefore` Radiation pressure `P=(I)/(c )-(-(I)/(c ))=(2I)/(c )`
Here P is between `(I)/(c )` and `(2I)/(c )`.
Hence, option (A, C, D) are correct.