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 pressurre is in the range I/c lt P lt 2I/c for real surfaces.

Answer

A, C, D

Explanation

Radiation pressure is given by
`p=("Force exerted by EM wave ")/("Area of surface ")`= Rate of change of momentum per unit area of surface.
Momentum per unit time, per unit area is given by
`("Intensity")/("Speed of wave ")=(I )/(c )`
Change in momentum per unit time per unit area =
`( I)/(c ) =p`
`। p=(I )/(C )`
Momentum per unit time, per unit area of incident wave is
` p.=(I )/(c)`
If the wave is totally absorbed, then momentum of the reflected wave per unit time, per unit area = 0
Radiation pressure (p) = Change in momentum per unit time per unit area
`=(I) /(c ) -0 =(I )/(c )`
If the wave is totally reflected, then momentum of the reflected wave per unit time, per unit area,
`P_2 =- I//c`
Radiation pressure `(p) = P_1- P_2`
`=(I )/(C ) -((-I )/(c ))=(2I)/(c )`
Radiation pressure (p) is in the range `I//c lt p lt 2I//c`for real surfaces.