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 :

Both (A) and (R) are true and (R) is the correct explanation of (A)

Both (A) and (R) are true but (R) is not the correct explanation of (A)

Electromagnetic Waves PYQ — JEE Main 2025 · 29 Jan · Shift 1 · Q52 with Solution

View written solutionFree

Correct answer: C

Analyze the Assertion (A)

Assertion: Electromagnetic waves carry energy but not momentum.

This statement is false.

Electromagnetic waves carry:
- energy, and
- momentum as well.
For a photon, $E = h\nu$ and its momentum is $p = \frac{E}{c} = \frac{h\nu}{c} = \frac{h}{\lambda}$

Hence electromagnetic radiation definitely carries momentum. This is also verified experimentally by radiation pressure.

Therefore, Assertion (A) is false.
Analyze the Reason (R)

Reason: Mass of a photon is zero.

This statement is true.

A photon has:
- zero rest mass,
- but non-zero energy and non-zero momentum.
In relativity, for photons: $E = pc$

So even though the rest mass is zero, momentum is not zero.

Therefore, Reason (R) is true.
Match with the options
- 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 false but (R) is true ✅
- D: (A) is true but (R) is false ❌
Final Answer

The correct option is: $\boxed{\text{C}}$
Comparison with stored correct answer

Stored correct answer: C

My derived answer matches the stored answer.

View written solutionFree

Correct answer: C

Analyze the Assertion (A)

Assertion: Electromagnetic waves carry energy but not momentum.

This statement is false.

Electromagnetic waves carry:
- energy, and
- momentum as well.
For a photon, $E = h\nu$ and its momentum is $p = \frac{E}{c} = \frac{h\nu}{c} = \frac{h}{\lambda}$

Hence electromagnetic radiation definitely carries momentum. This is also verified experimentally by radiation pressure.

Therefore, Assertion (A) is false.
Analyze the Reason (R)

Reason: Mass of a photon is zero.

This statement is true.

A photon has:
- zero rest mass,
- but non-zero energy and non-zero momentum.
In relativity, for photons: $E = pc$

So even though the rest mass is zero, momentum is not zero.

Therefore, Reason (R) is true.
Match with the options
- 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 false but (R) is true ✅
- D: (A) is true but (R) is false ❌
Final Answer

The correct option is: $\boxed{\text{C}}$
Comparison with stored correct answer

Stored correct answer: C

My derived answer matches the stored answer.