1. Doppler Effect (Ch. 12 Sec 12 7 p.338 – 342)
Demo: Whirling Bell
Change in frequency of the sound from a moving object as the object moves past some observer.
Show Example of waves undergoing Doppler Effect

2. Doppler Effect
For a moving source of the sound the equation for the stationary observed frequency is:
f ‘ = v
v + us f
Where:
f ‘ = observed frequency
f = frequency of the source
v = speed of the sound
us = speed of source
+ is used when source is moving away from observer
- is used when source is moving towards from observer

3. Doppler Effect
For a moving observer the frequency of observed stationary sound source is:
f ‘ =
v + uo v f
Where:
f ‘ = observed frequency
f = frequency of the source
v = speed of the sound
uo = speed of observer
+ is used when observer is moving towards the source
- is used when observer is moving away from source

4. Doppler Effect Example 1
Calculate the range of frequencies of an ambulance siren that holds a frequency of 330 Hz if the ambulance drives past you at 38 m/s if the speed of sound is 340 m/s?
f ‘ = v
v + us f
f ‘ =
340 m/s
330 Hz
f ‘ =
330 Hz x 1.126
f ‘ =
330 Hz x
f ‘ =
371 Hz
f ‘ =
297 Hz

5. Doppler Effect Example 2
Calculate the range of frequencies of an stationary ambulance siren that holds a frequency of 330 Hz if you drive by the ambulance at 38 m/s if the speed of sound is 340 m/s?
f ‘ =
v + uo v f
f ‘ =
340
330 Hz
f ‘ =
330 Hz x 1.112
f ‘ =
330 Hz x 0.888
f ‘ =
366 Hz
f ‘ =
293 Hz

6. Doppler Effect Example 3
A jet aircraft is travelling at you with a speed of 150 m/s and is emitting a sound of a frequency of 2500 Hz. The speed of sound is 320 m/s at this location. What is the change in the plane’s frequency as it flies past you?
f ‘ = v
v + us f
f ‘ =
320
2500 Hz
f ‘ =
2500 Hz x 1.882
f ‘ =
2500 Hz x 0.681
f ‘ =
4705 Hz
f ‘ =
1702 Hz
Δf ‘ =
3000 Hz

7. Doppler Effect Sonic Boom
A special case of the Doppler effect where the object generating the wave is actually moving faster than the wave.
This creates a “bow” wave of a super-wave that follows the moving object
Sonic Boom Explanation
Video of a Sonic boom in flight.

8. Doppler Effect
Do Problems: #49 – 51, 53 – 55 on p. 348 – 349 of your text book
Note: For #55 beat frequency = Δf

9. Doppler Effect
Do Problems from p
# 38, 51, 52, 54
The End