Q25 of 32 Page 51

Show that the radiation pressure exerted by an EM wave of intensity I on a surface kept in vacuum is I/c.

Assume that the surface is exposed to electromagnetic radiations. So, all the radiations are allowed to fall normally on the given surface.


Let the intensity of the radiation is I and the area of the surface is A.


So, the energy received by the surface in each second is given by,


E = I. A


So, number of photons received by surface in each second is given by,



For the perfectly absorbing surface,


So, force is given by,


Pressure is given by,



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