The Doppler effect describes the change in the perceived frequency of a sound, light, or other type of wave when the wave's source and the observer move relative to each other. It is commonly experienced when a vehicle with a siren approaches and then moves away from an observer.
The perceived frequency (\(f'\)) is related to the emitted frequency (\(f\)) as follows:
\[ f' = f \cdot \frac{v + v_o}{v - v_s} \]
- \(f'\): Perceived frequency (Hz).
- \(f\): Emitted frequency (Hz).
- \(v\): Speed of the wave in the medium (m/s).
- \(v_o\): Speed of the observer (m/s), positive if moving toward the source.
- \(v_s\): Speed of the source (m/s), positive if moving away from the observer.
For sound waves, the speed of the wave in air (\(v\)) is approximately 340 m/s at room temperature.
Perceived Frequency by the Observer: -- Hz
Low Frequency
High Frequency