Question

question 1 of 10
how does the doppler effect cause a sirens pitch to increase as it approaches you?
a. sound waves are spread out, decreasing wavelength and increasing frequency.
b. sound waves are spread out, increasing wavelength and decreasing frequency.
c. sound waves are pushed closer together, increasing wavelength and decreasing frequency.
d. sound waves are pushed closer together, decreasing wavelength and increasing frequency.

Explanation:

When a siren approaches, the source of the sound (the siren) is moving towards the observer. This causes the sound waves to be pushed closer together. Since the speed of sound \(v = f\lambda\) (where \(v\) is the speed of sound, \(f\) is frequency, and \(\lambda\) is wavelength) and the speed of sound in air is approximately constant (assuming no change in air conditions), a decrease in wavelength \(\lambda\) (because waves are pushed closer) leads to an increase in frequency \(f\) (since \(f=\frac{v}{\lambda}\)). Pitch is related to frequency (higher frequency means higher pitch).

Answer:

D. Sound waves are pushed closer together, decreasing wavelength and increasing frequency.