Waves Ques 20
20. A hospital uses an ultrasonic scanner to locate tumours in a tissue. The operating frequency of the scanner is $4.2$ $ MHz$. The speed of sound in a tissue is $1.7 $ $km / s$. The wavelength of sound in tissue is close to
[1995]
(a) $4 \times 10^{-4} m$
(b) $8 \times 10^{-4} m$
(c) $4 \times 10^{-3} m$
(d) $8 \times 10^{-3} m$
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Answer:
Correct Answer: 20.(a)
Solution:
- (a) Frequency $(n)=4.2$ $ MHz=4.2 \times 10^{6} $ $Hz$ and
speed of sound $(v)=1.7 $ $km / s=1.7 \times 10^{3} $ $m /$ $s$.
Wave length of sound in tissue,
$\lambda=\frac{v}{n}=\frac{1.7 \times 10^{3}}{4.2 \times 10^{6}}=4 \times 10^{-4} $ $m$