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# A police car siren moving toward the stationary observer will have a _____ pitch than when it is travelling away from the same observer.A. HigherB. LowerC. LouderD. Softer E. Faster

Last updated date: 26th Feb 2024
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Hint: In physics, the sensation of frequency of the sound waves is commonly known as pitch of the sound and it’s directly proportional to the frequency of sound waves. A higher frequency sound will have more pitch than the wave having low frequency.

Let us examine the apparent frequency for stationary observers and will determine the pitch.Suppose the original frequency of the siren of police car is denoted by $\nu$ and the apparent frequency for the observer when police car is moving away from the observer denoted as $\nu '$ which is given as:
$\nu ' = \nu (\dfrac{{{V_{sound}}}}{{{V_{sound}} + {V_{source}}}})$
Where, ${V_{sound}}$ Is the speed of sound in air and ${V_{source}}$ is the speed of the source which is the police car in the given question.

Now, calculating the apparent frequency when source moves towards the stationary observer:
$\nu '' = \nu (\dfrac{{{V_{sound}}}}{{{V_{sound}} - {V_{source}}}})$
Now, we can see that Denominator in second case is less than in first case, which shows
$\nu '' > \nu '$
So, the frequency of the siren approaching the stationary observer is greater than the frequency of moving away from the siren.

Hence, the correct option is A.

Note: It should be remembered that pitch is just a representation of how high or low the frequency of sound wave is and frequency of sound wave for a relative observer is also affected by speed of wind when this speed of wind is comparative to the speed of source and speed of sound waves.