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Unformatted text preview: Solution for Homework 21 Light Solution to Homework Problem 21.1(Wavelength of AM Radio) Problem: The rock AM station out of Canada that I listened to while growing up in Michigan had a frequency of 1150kHz = 1 . 15 10 6 Hz . Calculate the wavelength of the radio wave from this station in air. (a) 870nm (b) 42m (c) . 0038m (d-Answer) 261m (e) Toby. Solution The wavelength is related to the frequency by c = f , so = c f = 3 10 8 m s 1 . 15 10 6 Hz = 261m Total Points for Problem: 3 Points Solution to Homework Problem 21.2(Critical Angle for Waveguide) Problem: You are building a waveguide out of a plastic tube. You do not want light to escape the tube if the beam makes an angle of 25 with the normal of the side of the tube. The tube is in air. Calculate the minimum index of refraction required for material of the waveguide. (a) Cant be done. (b-Answer) 2 . 37 (c) . 42 (d) 1 . 55 (e) Toby. Solution This is a straight application of the critical angle, c . By Snells Law, n i sin i = n t sin t For light not to escape, t = 90 , so n i = n t sin 90 sin i = 1 sin 25 = 2 . 37 Total Points for Problem: 3 Points Solution to Homework Problem 21.3(Refraction from Super Material) Problem: Suppose orange light, wavelength 600nm in vacuum is incident at an angle of 70 to the normal for a material with index of refraction 50 . Calculate the angle of refraction. 1 (a) . 019 (b-Answer) 1 . 07 (c) 1 . 4 (d) The light does not refract. (e) Toby. Solution Just apply Snells law, n i sin i = n t sin t sin 70 = 50 sin t t = 1 . 07 Total Points for Problem: 3 Points Solution to Homework Problem 21.4(Fish Tank Critical Angle) Problem: You are using a red laser pointer to shine light into a fish tank. What is the maximum angle the light can make with respect to the normal, as the light passes from the glass ( n = 1 . 5 ) to the water ( n = 1 . 3333 )?...
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