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? 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 < p < 2I/c for real surface
Correct options are A) , C) and D) The cange in momentum per unit time is given as: p=speed of waveintensity=cI When the wave is fully absorbed by the surface, the momentum of the reflected wave per unit time per unit area =0 . So, Radiation pressure when wave is absorbed is: p = change in momentum per unit time per unit area i.e. cΔI=cI−0⇒cI When the wave is totally reflected, then the momentum of the reflected wave per unit time per unit area =−CI So, Radiation pressure for case of reflected wave: p=cI−(−cI)⇒c2I The radiation pressure for a real surface lies between the perfectly absorbing and perfectly reflecting surface. So, for real surface p lies between cI and c2I.
