## College Physics (7th Edition)

a). $7.5\times10^{-5}m$ b). $1.5\times10^{-2}m$
Medical ultrasound uses a frequency of around 20MHz to diagnose human conditions and ailments. a). Speed of sound in tissue = 1500m/s f=20MHz So, smallest detectable length is the wavelength. So, wavelength = $\frac{1500}{20\times10^{6}}$ Wavelength =$7.5\times10^{-5}m$ b). 200 times the wavelength is the penetrable depth. Penetration depth = $200\times7.5\times10^{-5}m=1.5\times10^{-2}m$