Photon

VITEEE 2015 Preparation › Mechanics questions › Photon

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.

#Physics #Mechanics

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2 Answers

21

Swaraj Dalmia ·2012-03-23 11:06:58

Using doppler effect [wave nature of light]
Here the source is moving with velocity v.
Î»'=Î»-vT
c/f'=(c-v)/f
f'/f=c/(c-v)
(f'-f)/f=v/(c-v)
Î”f/f=v/(c-v)â‰ˆv/c

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71

Vivek @ Born this Way ·2012-03-23 22:47:43

Damm.. I didn't approximate at the last step.

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