1.Whose Law is this?
The Relative frequency of a reflected wave increases as the relative motion of the
reflector approaches the observer:
Answer:
b. Doppler principle.
Doppler ultrasound measures the velocity of any SUPER reflectant object/fluid by evaluating the change of frequency of the reflected ultrasound. You have heard a Doppler frequency shift. When a whistling train approaches, you hear the "eeee" sound. As soon as it passes, the frequency of the whistle suddenly drops to a "oooo." This change to a lower pitch is because approaching objects compress the sound waves to make them sound higher in pitch. Objects moving away, rarify reflected sound waves and thus sound lower in pitch.
See: Curry, Chapter on
"Ultrasound."
Keywords: Doppler principle
