using the diagram at the right and thinking of what you have already leaned about the relationship between frequency and the wavelength of a sound wave, complete the two sentences here:

a. as a moving sound source approaches a stationary observer, the frequency of the sound increases, therefore the wavelength is_(longer or shorter)

b. As the sound source moves away from the observer, the pitch of the sound and the wavelength _____.

This effect is known as Doppler effect. When a moving sound source approaches a stationary observer, the wavefronts of the wave appear to be closer to each other: as a result, the frequency of the sound wave appears to be increased. The wavelength of the sound is inversely proportional to the frequency:

[tex]\lambda=\frac{v}{f}[/tex]

where v is the speed of the wave and f the frequency: therefore, as the frequency increases, the wavelength gets shorter.

b. As the sound source moves away from the observer, the pitch of the sound decreases and the wavelength increases

Explanation:

When the sound source moves away from the observer, the effect is opposite: the wavefronts appear to spread apart from each other, so the frequency of the sound appears to decreases, and as a result, the wavelength increases.

The pitch of a sound is related to how we perceive the sound, and it is directly proportional to the frequency: therefore, since the frequency decreases, the pitch decreases as well.