A monochromatic beam of light of frequency \( 5.0\times10^{14} \) Hz is produced by a laser source. What will be the energy of a photon in the light beam?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 33.15\times10^{-20} \) J
The energy of a photon is fixed by its frequency (Planck’s relation), with \( h = 6.63\times10^{-34}\ \mathrm{J\,s} \).
\( E = h\nu \)
\( E = (6.63\times10^{-34}\ \mathrm{J\,s}) \times (5.0\times10^{14}\ \mathrm{Hz}) \)
\( E = 3.315\times10^{-19}\ \mathrm{J} = 33.15\times10^{-20}\ \mathrm{J} \)
Note: NTA picked this question from an NCERT (2026-27) example and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Particle Nature of Light: The Photon – …
