Question

A hospital uses an ultrasonic scanner to locate tumors in a tissue. What is the wavelength of the sound in a tissue in which the speed of the sound is $1.7km/s$. the operating frequency of the scanner is $4.2MHz$. ( $1MHz={10}^{6}Hz)$

• A. $4.05\times {10}^{-4}m$
• B. $9.05\times {10}^{-4}m$
• C. $6.05\times {10}^{-4}m$
• D. $4.05\times {10}^{4}m$

Answer 1

The correct option is A $4.05\times {10}^{-4}m$

Given $f=4.2MHz=4.2\times {10}^{6}Hz$

Speed $v=1.7km/s=1.7\times {10}^{3}m/s$

Since $v=f\lambda ⟹\lambda =\frac{1.7\times {10}^3}{4.2\times {10}^6}=4.05\times {10}^{-4}m$