Doppler Effect

The Doppler Effect

​Mr EP

the change in frequency or wavelength of a wave observed when the source of the wave is moving towards or away from the observer (or the observer is moving relative to the source

The Doppler Effect

Observed Frequency for moving away or reciding source

​Fo = observed frequency (Hz)
Fs = Source frequency (Hz)
v = speed of wave (m/s)
vs = speed of source (m/s)

​Fo = observed frequency (Hz)
Fs = Source frequency (Hz)
v = speed of wave (m/s)
vs = speed of source (m/s)

Observed Frequency for moving forward or approaching source

Doppler Effect

(+) if the source is moving away
(-) If the source is moving toward or approaching

Multiple Choice

A train with a whistle that emits a note of frequency 800 Hz is approaching a stationary observer at a speed of 60 m s⁻¹. Calculate the frequency of the note heard by the observer. speed of sound in air = 330 m s⁻¹

• 980 Hz

• 970 Hz

• 1080 Hz

• 1090 Hz

Dropdown

a plane’s engine emits a note of constant frequency 120 Hz. It is flying away from a stationary observer at a speed of 80 m s^–1. Speed of sound in air = 330 ms⁻¹.

the observed wavelength of the sound received by the observer is ​

Select answer

m

observed frequency is ​

Select answer

Hz

Multiple Choice

An observer is situated at the top of a tall tower. An aero plane emitting sound at a frequency of 1000 Hz approaches the observer at a speed of 165 ms^–1. The speed of sound is 330 ms^–1. What is the frequency of the sound received by the observer?

• 330 Hz

• 667 Hz

• 1000 Hz

• 2000 Hz

Multiple Choice

A buzzer emitting sound of frequency 846 Hz is attached to a string and rotated in a horizontal circle. The linear speed of the buzzer is 25.0 ms^–1. The speed of sound is 340 ms^–1. What is the maximum frequency heard by the observer?

• 783 Hz

• 788 Hz

• 908 Hz

• 913 Hz

Multiple Choice

A source of sound of frequency F at point Z is moving at a steady speed. The pattern of the emitted wavefronts is shown.

• A

• B

• C

• D

Multiple Choice

The warning signal on an ambulance has a frequency of 600 Hz. The speed of sound is 330 ms^–1. The ambulance is travelling with a constant velocity of 25 ms^–1 towards an observer. The ambulance passes, and then moves away from the observer with no change in velocity.

Which overall change in observed frequency takes place between the times at which the ambulance is a long way behind the observer and when it is a long way in front of the observer?

• 49 Hz

• 89 Hz

• 91 Hz

• 98 Hz