If source and observer are moving towards each other with a velocity `v_("radial")` anf c indicates velocity of light, then, fractional change in frequency of light due to Doppler's effect will be

Options

A. `(Deltav)/v=(v_("radial"))/c`
B. `(Deltav)/v=(-v_("radial"))/c`
C. `(Deltav)/v=c/(v_("radial"))`
D. `(Deltav)/v=(-c)/(v_("radial"))`

Answer

B

Explanation

For velocities small compared to the speed of light. The fractional change in frequency `Deltav//v` is given by `-v_("radial")//c`, where `v_("radial")` is the component of the source velocity along the line joining the observer to the source relative to the observer, `v_("radial")` is considered positive when the source moves away from the observer. Thus, the Doppler shift can be expressed as, `(Deltav)/v=-(v_("radial"))/c`