The Doppler Effect is refers to a change in the frequency of radiation as it moves away/toward from the radiation. This effect produces a sudden change in pitch that is noticeable in a passing siren. In the above case, Doppler Effect is clearly explains why sound is heard more loudly and faintly once the object is moving away from the subject.
Therefore, as the oncoming sound waves approaching do possess high frequency and closeness of waves with higher amplitude in the above case. The ambulance is approaching with siren that causes higher frequency of sound waves due to Doppler Effect.
Doppler ultrasonography is a diagnostic procedure that uses high-frequency sound waves. The transducer releasing the sound waves is placed over an artery and uses Doppler technique to produce an audible sound as the blood flows through an artery.
Thus, the options (b), (c) and (a) are incorrect.
The Doppler Effect is refers to a change in the frequency of radiation as it moves away/toward from the radiation. This effect produces a sudden change in pitch that is noticeable in a passing siren. In the above case, Doppler Effect is clearly explains why sound is heard more loudly and faintly once the object is moving away from the subject.
Therefore, the correct option is – d. The Doppler Effect explains the rationale for why sound is heard initially more strongly and then faintly after moving object has passed.