Light travels in the form of photons. Identify the correct statements
(A) Photons travel with the velocity of light in vacuum.
(B) The rest mass of photons is taken as zero.
(C) Photons have energy which depends on frequency.
(D) Photons have a momentum inversely dependent on frequency.
Choose the correct answer from the options given below.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B) and (C) only
In the photon picture of light, a photon of frequency \( \nu \) has energy \( E = h\nu \) and momentum \( p = h\nu/c = h/\lambda \).
(A) Photons travel with the velocity of light in vacuum. — Correct. A photon moves at \( c \) in every frame and never at rest.
(B) The rest mass of photons is taken as zero. — Correct. A particle moving at the speed of light must have zero rest mass.
(C) Photons have energy which depends on frequency. — Correct. \( E = h\nu \).
(D) Photons have a momentum inversely dependent on frequency. — Incorrect. \( p = h\nu/c \) is directly proportional to the frequency; it is inversely proportional to the wavelength.
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.”