Question

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 :

• A. Both (A) and (R) are true and (R) is the correct explanation of (A)
• B. Both (A) and (R) are true but (R) is not the correct explanation of (A)
• C. (A) is true but (R) is false
• D. (A) is false but (R) is true

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Electromagnetic waves carry momentum ($p = U/c$). When they hit a surface, they transfer this momentum, creating radiation pressure. They are composed of photons which have zero rest mass.
Step 2: Detailed Explanation:
Assertion: True. Radiation pressure $P = I/c$ (for total absorption) or $2I/c$ (for reflection) exists because EM waves carry momentum.
Reason: True. Photons have zero rest mass. Energy is related to frequency, not mass.
Explanation check: The pressure exists because of momentum, not because of the absence of mass. Therefore, (R) is not the reason why (A) is true.
Step 3: Final Answer:
Both are true but (R) is not the correct explanation of (A).