Suppose frequency of emitted photon is of when electron of a stationary hydrogen atom jumps from a higher state m to a lower state n. If the atom is moving with a velocity `v(lt lt c)` and emits a photon of frequency f during the same transition, then which of the following statements are possible.

Options

A. f may be equal to `f_(0)`
B. f may be greater than `f_(0)`
C. f may be less than `f_(0)`
D. f cannot be equal to `f_(0)`

Answer

A, B, C

Explanation

It photon is emitted perpendicular to v, `f=f_(0)` because same part of energy of transition goes to recoil KE of the hydrogen as in the stationary atom. If photon is emitted in same direction as `v, f gt f_(0)` because now KE of the H atom decreases due to recoil. and it photon is emitted opposite to `v, f lt f_(0)` because KE of H atom increases due to recoil, the increase here is more than in a stationary atom .