Question

A hospital uses an ultrasonic scanner to locate tumours in a tissue. The operating frequency of the scanner is $4.2$ $M{H}_z$. The speed of sound in a tissue is $1.7$ $km/s$. The wavelength of sound in tissue is close to

• A. $4\times {10}^{-4}$ $m$
• B. $8\times {10}^{-4}$ $m$
• C. $4\times {10}^{-3}$ $m$
• D. $8\times {10}^{-3}$ $m$

Answer 1

The correct option is A $4\times {10}^{-4}$ $m$

Given:
Frequency $\left(f\right)=4.2$ $M{H}_z=4.2\times {10}^6$ $H_z$
Speed in tissue $\left(v\right)=1.7$ $km/s=1700$ $m/s$
$\therefore$ Wavelength $=\lambda \times f=v$
$\lambda =\frac{v}{f}=\frac{1700}{4.2\times {10}^6}=4\times {10}^{-4}$ $m$