According to the Doppler Effect, which statement is true about a sound as it approaches you and then moves away.

A) As the source approaches you, the waves are compressed so that the pitch of the noise increases.  

Explanation:

The Doppler Effect occurs when there is relative motion between an observer and the source of a wave. When this happens, there is an apparent shift in the frequency of the wave, as perceived by the observer. In particular, two situations can occur:

1- If the source of the wave is moving towards the observer, the waves are compressed, so that the wavelength of the wave decreases, and therefore the frequency (and so the pitch) increases

2- If the source of the wave is moving away from the observer, the waves are stretched, so that the wavelength of the wave increases, and therefore the frequency (and so the pitch) decreases

An example of Doppler Effect occurs when we hear the sound of the siren of an ambulance.

In this problem, the situation described is situation 1 (sound waves is approaching the observer), so according to the explanation above, the correct answer is

A) As the source approaches you, the waves are compressed so that the pitch of the noise increases.

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