7. •• Medical ultrasound uses a frequency of around 20 MHz to diagnose human conditions and ailments by reflection. Objects and structures down to the size of the wavelength can be detected using these waves.

(a) If the speed of sound in tissue is 1500 m/s, estimate the smallest detectable object.

(b) If the penetration depth in tissue is about 200 wavelengths, how deep can these waves penetrate into tissue?