Question

Which of the following is false with respect to photons?

• A. A photon always travels at a speed $=3\times {10}^8\text{m/s}$ in vacuum (from any frame of reference used to observe the photon)
• B. Rest mass of a photon is zero.
• C. Total momentum and energy is conserved when a photon collides with material particle.
• D. Total number of photons, in all situations, is conserved.

Answer 1

The correct option is D Total number of photons, in all situations, is conserved.

The photons may get absorbed and/or new photon may be emitted by any object or surface.

Thus, the total number of photons in a situation may not be conserved.

Hence, $\left(D\right)$ is the correct answer.

Why this question? This question tests basic knowledge of photon and light's particle nature.