Monochromatic light of frequency 6.0 × 1014 Hz is produced by a laser. The power emitted is 2.0 × 10–3 W. (i) What is the energy of a photon in the light beam? (ii) How many photons per second, on an average, are emitted by the source?
(i) Energy emitted by a photon = hν = (6.63 x 10-34 x 6 x 1014) J = 39.78 x 10-20 J = 2.49 eV, where h = Planck’s constant, ν = frequency.
(ii) Total power = 2 x 10-3 W(given)
Therefore, number of photons per second = 
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