# Need help with This Physics 3 Soundwave Question?

The Doppler effect is the shift in frequency of sound waves when there is motion of the source of sound, the listener, or both. Fs is the frequency of sound waves from the source.

a. Assume that the listener does not move. Find the frequency of sound waves that the listener detects (Fl) when the source of sound is moving towards the listener.

b. Assume that the listener does not move. Find the frequency of sound waves that the listener detects (Fl) when the source of sound is moving away from the listener.

c. Based on your findings in a and b, explain why you hear the higher pitch of the siren of the approaching ambulance, and notice that its pitch drops suddenly as the ambulance passes you.

d. Assume that the listener is moving towards the source of sound. Find the frequency of sound waves that the listener detects (Fl) when the source of sound is moving towards the listener.

e. Assume that the listener is moving away from the source of sound. Find the frequency of sound waves that the listener detects (Fl) when the source of sound is also moving away from the listener.

Fl is F subscript l Thanks.

Relevance

Doppler:

Fl = F₀*(V + Vr)/(V + Vs)

f is perceived frequency

F₀ is actual frequency

V is the speed of sound

Vr is positive if the receiver is moving toward the source, and

Vs is negative if the source is moving toward the receiver

a. When the listener is stationary, Vr = 0 and

Fl = F₀*V/(V - Vs)

b. Fl = F₀*V/(V + Vs)

c. Because the denominator switches from < V to > V, decreasing the perceived frequency.

d. Fl = F₀*(V + Vr)/(V - Vs)

e. Fl = F₀*(V - Vr)/(V + Vs)

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