Heart Sonogram. Physicians use high-frequency 1f = 195 MHz2 sound waves, called ultrasound, to image internal organs. The speed of these ultrasound waves is 1480 m>s in muscle and 344 m>s in air. We define the index of refraction of a material for sound waves to be the ratio of the speed of sound in air to the speed of sound in the material. Snells law then applies to the refraction of sound waves. (a) At what angle from the normal does an ultrasound beam enter the heart if it leaves the lungs at an angle of 9.73 from the normal to the heart wall? (Assume that the speed of sound in the lungs is 344 m>s.) (b) What is the critical angle for sound waves in air incident on muscle?
Week 6 Thursday, September 29, 2016 11:13 AM If there is no EF inside conducting material, e-'s move randomly If field is present, e- force F=-eE imposes small drift on e-'s motion Zig-zag line represent motion of charge carrier in conductor ○ Avg speed: ○ Drift speed: (much smaller) ○ Current (I) is opp dir of net displacement of e-'s Macroscopic currents can be related to motion of microscopic charge carriers making up the current ○ Current depends on: avg drift speed of charge carriers in the dir of the current # of charge carriers per unit volume Size of charge carried by each ○ Consider identically cha