Consider an excited hydrogen atom in state n moving with a velocity `upsilon(upsilon lt lt c)`. It emits a photon in the direction of its motion and changes its state to a lower state m. Apply momentum and energy conservation principle to calculate the frequency v of the emitted radiation, compare this with the frequency `v_(0)` emitted if the atom were at rest.

Answer

A, C

Explanation

Velocity of hydrogen atom is state `'n' =u` also the velocity of photon `=u`
But `ult ltc`
Here the photon is emitted as a wave. So its velocity is same as that of hydrogen atom i.e. u.
:. According to Doppler's effect.
Frequency `v=v_0((1+u/c)/(1-u/c))`
As `ult lt ltc`, `1-u/c =q`
:. `v=v_0((1+u/c)/(1))`
`=v_0(1+u/c)`
`v=v_0(1+u/c)`