The Doppler Effect
15.7 The Doppler Effect
Learning Objectives
By the end of this section, you will be able to:
- Explain the change in observed frequency as a moving source of sound approaches or departs from a stationary observer
- Explain the change in observed frequency as an observer moves toward or away from a stationary source of sound
Practice!
| Practice 15.7.1 |
|---|
 Consider detectors of water waves at three locations A, B, and C in the figure. Which of the following statements is true? |
| (a) The wave speed is highest at location A. |
| (b) The wave speed is highest at location C. |
| (c) The detected wavelength is largest at location B. |
| (d) The detected wavelength is largest at location C. |
| (e) The detected frequency is highest at location C. |
| (f) The detected frequency is highest at location A. |
| Practice 15.7.2 |
|---|
| If a 1.00-kHz sound source moves at a speed of 50.5 m/s toward a listener who moves at a speed of 25.0 m/s in a direction away from the source, what is the apparent frequency heard by the listener? (Use 343 m/s as the speed of sound in air.) |
| (a) 808 Hz |
| (b) 935 Hz |
| (c) 1000 Hz |
| (d) 1087 Hz |
| (e) 1258 Hz |
Discuss!
The frequency of the train whistle when the train is not moving is 495 Hz. What sound frequency does each person hear?
A bat flying 9.00 m/s emits a 65.0 kHz sound wave. It reflects off a moth fleeing at 2.00 m/s in the same direction the bat is flying. What frequency does the bat hear when the sound returns?
You are at an outdoor concert with a wind blowing at 10 m/s from the performers toward you. Is the sound you hear Doppler-shifted? If so, is it shifted to lower or higher frequencies?
Physics Education Research at UNG 