Lesson: The Doppler EffectPhysics
In this lesson, we will learn how to calculate the change in the frequency of waves that are emitted by a source that is moving relative to the observer.
Sample Question Videos
A hawk swoops down to catch a mouse, screeching as it does so. The hawk approaches the mouse at a speed of 25.0 m/s, and the frequency of the screech is 3,500 Hz. What is the frequency of the screech as heard by the mouse? Use a value of 331 m/s for the speed of sound in air.
A commuter train approaches a crossing and blows its horn to make a note of frequency 200 Hz. An observer at the crossing measures the frequency of the train’s horn as 208 Hz. The speed of sound in the train’s vicinity is 335 m/s.
What is the speed of the train?
If the train’s speed remains constant, what frequency does the observer measure as the train recedes from them?
An ambulance’s siren has a frequency of 1.00 kHz. The ambulance is approaching the scene of an accident at a speed of 70.00 mph. A nurse is approaching the scene from the opposite direction to the ambulance at a speed of 7.00 m/s. Determine the frequency of the siren as measured by the nurse. Use a value of 343.00 m/s for the speed of sound in the region around the accident scene.