GATE 2025 PH – Question 25
Which of the following option(s) is/are correct for photons?
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: (A) Its rest mass is zero, but its energy is non-zero; (B) It carries non-zero linear momentum; (D) It has two linearly independent states of polarization
Explanation
Check each statement about photons.
- **A. Rest mass is zero but energy is non-zero.** True. The energy is $E=h\nu=pc$. ✓
- **B. It carries non-zero linear momentum.** True: $p=h\nu/c=h/\lambda$. ✓
- **C. It carries zero spin angular momentum.** False. The photon is a spin-1 particle.
- **D. It has two linearly independent polarisation states.** True. Being massless, it has only two transverse polarisations (not three). ✓
Answer **A, B and D**.