Write the formula\'s and explain why they are used in this situation. Explain ea
ID: 1648216 • Letter: W
Question
Write the formula's and explain why they are used in this situation. Explain each variable and how you know that the variable represents that quantity. Use definitions and key terms to explain solution.
Ultrasound machines use high-frequency sound waves (f-1-5MHz) to image internal organs. These waves travel at 344m/s in air and 1480m/s in muscle. (a) Using Snell's Law, 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 the lungs are full of air) (b) What is the critical angle for sound waves in air incident on muscle?Explanation / Answer
A) Here we can use laws of refraction of sound just like in light.
Refractive index of muscles or heart n2 = velocity in air/velocity in muscles
n2 = 344/1480
= 0.2324
Refractive index of air n1 is taken as 1.
By snells law, n1 sin i = n2 sin r
1* sin 9.73 degree = 0.2324 sin r
r = arcsin (sin 9.73 degree /0.2324)
= 46.65 degree
B) Let critical angle be C.
At this angle, r= 90 degree
1*sin C = 0.2324 sin 90 degree
C = arcsin (0.2324)
= 13.44 degree answer
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