Ultrasound is absorbed in the body; this complicates the use of ultrasound to im

Question

Ultrasound is absorbed in the body; this complicates the use of ultrasound to image tissues. The intensity of a beam of ultrasound decreases by a factor of 2 after traveling a distance of 40 wavelengths. Each additional travel of 40 wavelengths results in a decrease by another factor of 2. Assume speed of ultrasound in human tissue = 1540 .

A beam of 1.5 ultrasound begins with an intensity of 2000 . After traveling 15 through tissue with no significant reflection, the intensity is about
A) 13
B) 20
C) 160
D) 320


Part B
A physician is making an image with ultrasound of initial intensity 2000 . When the frequency is set to 1.5 , the intensity drops to 1000 at a certain depth in the patient's body. What will be the intensity at this depth if the physician changes the frequency to 3.0 ?
A) 250
B) 500
C) 1000
D) 2000


Part C
A physician is using ultrasound to make an image of a patient's heart. Increasing the frequency will provide
A) more penetration but worse resolution.
B) less penetration and worse resolution.
C) better penetration and better resolution.
D) less penetration but better resolution.


Part D
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.

Explain please

Explanation / Answer

answer to part D as you are supposed to ask only one question The beat frequency is just the difference between the frequency of the wave reflected from a stationary and a moving object. beat frequency/base frequency = relative velocity/wave velocity so, as the base frequency increases, so must the beat frequency. Another way to think of this is counting the frequency of the "extra" beats caused by the source moving toward you. If you try the experiment with a source emitting wave fronts very frequently, you'd expect to measure more "extra" beats.

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