A physician is using Doppler ultrasound to measure the motion of a patient's heart. The device measures the beat frequency between the emitted and the reflected waves. Increasing the frequency of the ultrasound will

A. Increase the beat frequency.

B. Not affect the beat frequency.

C. Decrease the beat frequency.

(A) Increasing the frequency of the ultrasound will increase the beat frequency.

Explanation:

When a physician uses Doppler ultrasound to measure the motion of a patient's heart. The device measures the beat frequency between the emitted and the reflected waves as frequency shift. This frequency shift is known as Doppler effect.

In Doppler effect, the relationship between the received frequency F and the transmitted frequency F₀ is given by

F = [ (C+Vt) / (C-Vs) ]F₀

From the equation above, received frequency F is directly proportional to the transmitted frequency F₀.

Also, Beat frequency = 2v/λ

Frequency is directly proportional to velocity, so increase in frequency increases velocity of the sound, which increases the beat frequency.

There, Increasing the frequency of the ultrasound will increase the beat frequency.