An electromagnetic 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 the force exerted by electromagnetic wave on unit area of the surface,i.e., rate of change of momentum per unit area of the surface .
Momentum per unit time per unit area
`=("intensity")/("Speed of wave") = I/C`
Change in momentum per unit time per unit area `=(DeltaI)/(C )=`radiation pressure (p).
`i.e.," "p =(DeltaI)/(C)`
Momentum of incident wave per unit time per unit area `=(I)/(C )`
when wave is fully absorbed by the surface , hte momentum of the reflected wave per unit time per unit area=0
Radiation pressure (p) = change in momentum per unit time per unit area `=(DeltaI)/(C) =(I)/(C) -0 =(I)/(C)`
When wave is totally reflected then momentum of the reflected wave per unit time per unit area `=(I)/(C)` Radiation pressure `p=I/C -(- (I)/(C))= (2I)/(C)`
Here p lies between `(I)/(C) " and " (2I)/(C)`.