Question

A hospital uses an ultrasonic scanner to locate tumors in a tissue. The operating frequency of the scanner is $4.2 \, MHz$. The speed of sound in a tissue is $1.7 \, km \, s^{-1}$. The wavelength of sound in the tissue

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

Answer 1

Answer: (C)

$4 \times 10^{-4} m$

Answer 2

Here, $\upsilon = 4.2 \, MHz = 4.2 \times 10^6 \, Hz$
$v= 1.7 \, km \, s^{-1} = 1.7 \times 10^3 m \, s^{-1}$
Wavelength
$\lambda = \frac{v}{\upsilon} = \frac{1.7 \times 10^3 m \, s^{-1}}{4.2 \times 10^6 \, s^{-1}} = 4 \times 10^{-4} m$