# Question #d50a0

Jun 29, 2016

D) distance of source from listener

#### Explanation: Doppler effect is the apparent change observed by an observer in the frequency of a wave (such as light or sound) whenever the source of the wave is moving relative to the observer.

The figure above shows Doppler effect for Sound. As the source of sound moves towards the listener the the pitch appears higher and as the source moves away the pitch appears to decrease.

the relationship between heard frequency $f$ and emitted frequency ${f}_{0}$ is given by the following expression
$f = \frac{v + {v}_{r}}{v + {v}_{s}} {f}_{0}$
where
$v$ is the velocity of waves in the medium,
${v}_{r}$ is the velocity of the receiver relative to the medium. It is taken as positive if the receiver is moving towards the source and negative if moving away from source,
${v}_{s}$ is the velocity of the source relative to the medium. It is taken as positive if the source is moving away from the receiver and negative if moving towards the receiver.

From the equation we see that it is independent of the distance of source from listener.