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Unformatted text preview: Solution for Homework 21 Light Solution to Homework Problem 21.1(Transmission of Super Material) Problem: If sunlight with intensity 1000W / m 2 shines on an engineered material with index of refraction 50 at normal incidence, calculate the intensity of the light that is transmitted into the material. (a) 39W / m 2 (b) 961W / m 2 (c-Answer) 77W / m 2 (d) 923W / m 2 (e) Toby. Solution The intensity of the reflected light is given by I r = parenleftbigg n i- n t n t + n i parenrightbigg 2 I = parenleftbigg 1- 50 1 + 50 parenrightbigg 2 (1000W / m 2 ) = 923W / m 2 By conservation of energy the transmitted intensity is I t = I- I r = 77W / m 2 Total Points for Problem: 3 Points Solution to Homework Problem 21.2(Light, sun, and the former planet Pluto) Problem: Pluto is Mickey’s dog. Forget that. Try Again. The (now former) planet Pluto at its farthest distance from the Sun is a distance of 7 . 35 × 10 12 m from the Sun. How far is that in dog years? The real question is how long does it take light to reach Pluto from the Sun at this distance. This is a question asked by a student in the lecture quiz on the first lecture day. (a) . 150s (b-Answer) 24500s = 6 . 8hours (c) 125 , 000s = 35hours (d) 0s . Light reaches Pluto instantaneously. (e) Toby. Solution The speed of light is c = 2 . 99 × 10 8 m / s . Time equals distance divided by speed, so we have t = d c = 7 . 35 × 10 12 m 2 . 99 × 10 8 m / s = 24 . 5 × 10 3 s This is almost seven hours....
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