The speed of sound in biological tissue is 1500 m/s. To resolve features with sizes of the order of two millimeters, the frequency of the sound wave used by a doctor is A) larger than 3.0 $\times$ 10⁵ Hz. B) smaller than 3.0 $\times$ 10⁵ Hz. C) 7.5 $\times$ 10⁵ Hz. D) larger than 7.5 $\times$ 10⁵ Hz. E) smaller than 7.5 $\times$ 10⁵ Hz.

Question

Quizplus · Accepted Answer

To resolve features of 2 mm, the wavelength should be about 2 mm or smaller. Using the speed of sound $v = 1500 \, \text{m/s}$ and the wavelength $\lambda = 0.002 \, \text{m}$, the frequency $f$ is given by $f = \frac{v}{\lambda} = \frac{1500}{0.002} = 750,000 \, \text{Hz}$ or $7.5 \times 10^5 \, \text{Hz}$. To resolve features of this size, the frequency must be larger than this value.

The Speed of Sound in Biological Tissue Is 1500 M/s ×\times×

The Speed of Sound in Biological Tissue Is 1500 M/s $\times$