JEE Physics 2025 Question with Solution

Given: Assertion (A): Electromagnetic waves carry energy but not momentum.

Find: Which option correctly evaluates Assertion (A) and Reason (R).

Electromagnetic waves carry both energy and momentum. For a photon, momentum and energy are related by

$$p = \frac{E}{c}$$

So the statement that electromagnetic waves carry energy but not momentum is false.

Reason (R): Mass of a photon is zero.

This statement is true. A photon has zero rest mass, yet it still carries momentum and energy.

Therefore, Assertion (A) is false but Reason (R) is true. The correct option is B.

Given: Assertion (A): Electromagnetic waves carry energy but not momentum.

Find: The most appropriate answer from the given options.

First analyze Assertion (A). Electromagnetic waves are associated with energy transport, and they also possess momentum. For photons,

$$E = h\nu$$

and

$$p = \frac{E}{c}$$

Hence, electromagnetic waves do not carry only energy; they carry momentum as well. So Assertion (A) is false.

Now analyze Reason (R). The mass of a photon is zero. This is true.

However, zero rest mass does not mean zero momentum. A photon can have momentum even though its rest mass is zero.

So the correct evaluation is:

• Assertion (A) is false
• Reason (R) is true

Conclusion: The correct option is B.

Note: The provided page shows a contradictory textual statement in one place, but the worked analysis and the marked correct option identify Assertion (A) as false and Reason (R) as true.