Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Electromagnetic waves carry energy but not momentum. Reason (R ): Mass of a photon is zero. In the light of the above statements, choose the most appropriate answer from the options given below :

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

Answer 1

Answer: (D)

Assertion (A) is false but Reason (R) is true.

Answer 2

Assertion (A) is false. Electromagnetic waves carry both energy and momentum. The momentum ($p$) of an electromagnetic wave is related to its energy ($E$) by the relation $p = E/c$, where $c$ is the speed of light. This momentum transfer is responsible for phenomena like radiation pressure.

Reason (R) is true. Photons, which are the quanta of electromagnetic radiation, are considered to be massless particles; their rest mass is zero.