Final answer:
The change in frequency or wavelength due to relative motion between a sound source and a reflecting surface is called the Doppler effect. This phenomenon is characterized by a shift in frequency, known as a Doppler shift, as observed when there is relative motion between the source and the observer. The correct option is A.
Step-by-step explanation:
The term for the change of frequency or wavelength due to relative motion between a sound source and a reflecting surface is known as the Doppler effect. This effect can be observed when a sound source or an observer is moving relative to one another.
A classic example of the Doppler effect is when you hear the pitch of an ambulance siren change as it approaches and then passes by you. The actual change in frequency due to this motion is referred to as a Doppler shift.
The Doppler effect and Doppler shift are named after Christian Johann Doppler, an Austrian physicist who conducted experiments with both moving sources and moving observers, such as musicians on a train.