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)
Concept. EM waves carry momentum $p=\dfrac Uc$ (photon momentum $\dfrac h\lambda$) even though the photon has no rest mass. Momentum, not mass, is what produces radiation pressure.
Step 1. Assertion. True: a wave falling on a surface transfers momentum, so it exerts pressure.
Step 2. Reason. True: no mass is associated with EM waves.
Step 3. Explanation? No. Having no mass does not explain the pressure; the momentum carried by the wave does.
Answer. Both true, R not the correct explanation (Option B).
Solution by Sreeraj P, M.Sc Physics
