Which of the following are the properties of photons?
(A) The rest mass of a photon is zero
(B) Each photon has a definite energy and an indefinite linear momentum
(C) A photon may collide with a material particle and the total energy and the total momentum remain conserved in such a collision
(D) Photons are deflected by electric and magnetic fields
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) and (C) only
In the photon picture of light, each photon of frequency \( \nu \) has energy \( E = h\nu \) and momentum \( p = h\nu/c \), and it carries no charge.
(A) The rest mass of a photon is zero. — Correct. A photon always moves at the speed of light and has zero rest mass.
(B) Each photon has a definite energy and an indefinite linear momentum. — Incorrect. The momentum is just as definite as the energy: \( p = h\nu/c \).
(C) A photon may collide with a material particle and the total energy and the total momentum remain conserved in such a collision. — Correct. In a photon-electron collision both energy and momentum are conserved, although the number of photons need not be.
(D) Photons are deflected by electric and magnetic fields. — Incorrect. Photons are electrically neutral, so these fields do not deflect them.
NCERT (2026-27):
Particle Nature of Light: The Photon – “… (ii) Each photon has energy E (= hν) and momentum p (= hν/c), and speed c, the speed of light.”
Particle Nature of Light: The Photon – “… (iv) Photons are electrically neutral and are not deflected by electric and magnetic fields. (v) In a photon-particle collision (such as photon-electron collision), the total energy and total momentum are conserved.”