Question

Question #009a8

Answer 1

The Doppler effect for sound is used to find an observed frequency of 835 Hz.

Explanation:

The Doppler effect for sound tells us that in this case, where the listener is moving toward a stationary sound source, the observed frequency `f_l` will be given by

`f_l=(v+v_l)/v*f_s`

where `v` is the speed of sound and `v_l` is the speed the listener is moving. In this case

`f_l=(340.6+15)/340.6*800 = 835 Hz`

This is a 4.4% increase in frequency, which is readily noticeable by the listener, based on the fact that a semitone in music (C to C#, for instance) is a 5.9% increase.

Note that the equation used for calculating the observed frequency for a moving listener is not the same as the one used if the listener is stationary and the source is moving. In that case, you would use

`f_l=v/(v+-v_s)*f_s`

with the + sign used for the case where the distance between source and listener is decreasing, and the - sign used when the distance is increasing.