Question

Medical ultrasound uses a frequency of around 20 MHz to diagnose human conditions and oilments.

a) If the speed of sound in tissue is 1500 m/s, what is the smallest detectable object?

b) If the penetration depth is about 200 wavelengths, how deep can this instrument penetrate?

Answer 1

The size of the object should be greater than or equal to the wavelength for us to be able to detect it.
 v = fλ
1500 = 20* $10^{6}$λ
λ = 75*$10^{-6}$
Depth upto which the instrument can penetrate = 200* 75* $10^{-6}$
                                                                            = 0.015 m = 1.5 cm