Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : The electromagnetic wave exerts pressure on the surface on which they are allowed to fall.
Reason (R) : There is no mass associated with the electromagnetic waves.
In the light of the above statements, choose the correct answer from the options given below :
Answer: (B) Both (A) and (R) are true but (R) is not the correct explanation of (A)
(A) is true: EM waves carry momentum $p = \dfrac{U}{c}$, so they exert radiation pressure when absorbed or reflected.
(R) is taken as true in the official answer (EM waves have no rest mass), but it does not explain the pressure; the pressure comes from the momentum the wave carries.
Solution by Sreeraj P, M.Sc Physics