Identify the basic features of the photon picture of electromagnetic radiation from the following.
(A) Each photon has energy \( E = h\nu \) in vacuum.
(B) Photons are electrically neutral and are not deflected by electric and magnetic fields.
(C) All photons of light of a particular frequency \( \nu \) or wavelength \( \lambda \) have the same energy and momentum.
(D) If the intensity of light of a given wavelength is increased, there is an increase in the number of photons incident on a given area in a given time.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B), (C) and (D)
In the photon picture, radiation of frequency \( \nu \) consists of particles (photons), each carrying a fixed energy \( h\nu \) and momentum \( h\nu/c \).
(A) Each photon has energy \( E = h\nu \) in vacuum. — Correct. This is the energy of a photon; its momentum is \( p = h\nu/c \).
(B) Photons are electrically neutral and are not deflected by electric and magnetic fields. — Correct. A photon carries no charge, so no electric or magnetic force acts on it.
(C) All photons of light of a particular frequency \( \nu \) or wavelength \( \lambda \) have the same energy and momentum. — Correct. Both \( E = h\nu \) and \( p = h/\lambda \) depend only on the frequency (or wavelength), so photons of one frequency are identical in energy and momentum.
(D) If the intensity of light of a given wavelength is increased, there is an increase in the number of photons incident on a given area in a given time. — Correct. Each photon's energy is fixed by the wavelength, so a higher intensity can only mean more photons crossing unit area per unit time.
NCERT (2026-27):
Particle Nature of Light: The Photon – “… We can summarise the photon picture of electromagnetic radiation as follows: … (ii) Each photon has energy E (=hν) and momentum p (= hν/c), and speed c, the speed of light.
(iii) All photons of light of a particular frequency ν, or wavelength λ, have the same energy E (=hν = hc/λ) and momentum p (= hν/c= h/λ), whatever the intensity of radiation may be. By increasing the intensity of light of given wavelength, there is only an increase in the number of photons per second crossing a given area, with each photon having the same energy. …
(iv) Photons are electrically neutral and are not deflected by electric and magnetic fields.”