Answer – The Doppler effect is the phenomenon in which a stationary observer perceives a change in the frequency of waves produced by a moving source.
Explanation:
A person (stationary observer) standing by the side of a road at night watches as a car (moving wave source) drives by them. When the car was at a distance, the sound of its engine was low, as was the beam of its headlights. The engine got louder and the headlights got brighter as the car neared the observer. This is an example of the Doppler effect.
A wave source may be emitting waves of a steady frequency. If the source remains stationary, the waves it produces will be perceived as being regular or steady by an observer who is also stationary, regardless of the distance between the two. However, if either the observer or the source is moving while the other remains stationary, the observer will perceive a change in the wave frequency. The wave frequency is perceived as higher when the distance between the two is shorter, and lower when the distance is longer. This phenomenon is called the Doppler effect.
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