An excited atom of mass m and initial speed v emits a photon in its direction of motion. If v << c, show that the frequency of the photon is higher by \frac{\Delta f}{f} \approx \frac vc , than it would have been if the atom had been at rest.
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2 Answers
21Using doppler effect [wave nature of light]
Here the source is moving with velocity v.
λ'=λ-vT
c/f'=(c-v)/f
f'/f=c/(c-v)
(f'-f)/f=v/(c-v)
Δf/f=v/(c-v)≈v/c
