AP Physics 2: Algebra-Based Flashcards: The Doppler Effect
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
An ambulance siren sounds higher in pitch as it approaches you. Which aspect of the Doppler effect explains this?
This is explained by the principle that for a source moving toward an observer, the observed frequency is greater than the rest frequency, resulting in a higher perceived pitch.
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An ambulance siren sounds higher in pitch as it approaches you. Which aspect of the Doppler effect explains this?
This is explained by the principle that for a source moving toward an observer, the observed frequency is greater than the rest frequency, resulting in a higher perceived pitch.
As a train passes and moves away, its horn sounds lower in pitch. How does the Doppler effect account for this?
This occurs because for a source moving away from an observer, the observed frequency is less than the rest frequency, resulting in a lower perceived pitch.
A star's light is observed to have a lower frequency than expected (a 'redshift'). What does this imply about its motion relative to Earth?
This implies the star is moving away from Earth, as the observed frequency is less than the rest frequency for a receding source.
What fundamental factor causes the change in observed wave properties described by the Doppler effect?
The properties of a wave are based on the relative motion between the source of the wave and the observer of the wave.
What three variables are related by the Doppler effect?
The Doppler effect relates the rest frequency of a source, the observed frequency, and the relative velocity between the source and observer.
What is the relationship between observed frequency and rest frequency when a wave source moves AWAY from an observer?
For a wave source moving away from an observer, the observed frequency is less than the rest frequency.
What is the relationship between observed frequency and rest frequency when a wave source moves TOWARD an observer?
For a wave source moving toward an observer, the observed frequency is greater than the rest frequency.
If you observe a wave's frequency to be lower than its rest frequency, what is the relative motion of the source?
The wave source is moving away from you, the observer.
What is the Doppler effect?
The Doppler effect describes the relationship between the rest frequency of a wave source, the observed frequency of the source, and the relative velocity of the source and the observer.
If you observe a wave's frequency to be higher than its rest frequency, what can you conclude about the source's motion?
You can conclude that the wave source is moving toward you, the observer.