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Chapter 14 Refraction
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Section 14-1 Refraction ~ the bending of a wave as it passes at an angle from one medium into another. Refraction occurs because of a change in the wave speed.
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With light, if the speed decreases going from the first to the second material, the ray is bent towards the normal.
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If the speed increases in the second material, the ray is bent away from the normal.
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The index of refraction, n, is the ratio of the speed of light in a vacuum (c) to its speed in a given medium (v). Since c and v are both given in m/s the index of refraction has no units. The slower the speed, the more optically dense the medium is and the greater n is.
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Index of Refraction for Various Substances:
Water at 20 degrees C Ice at 0 degrees C Air at 0 degrees C CO2 at 0 degrees
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Medium 1 Medium 2 Incident Ray Refracted Ray Reflected Ray The relationship between the angles of incidence and refraction is given by Snell’s Law
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Snell’s Law n1(sin q1) = n2(sin q2)
n1= index of refraction for medium 1 q1 = incident angle n2 = index of refraction for medium 2 q2 = refracted angle
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Section 14-1 Practice Problem
A light ray of wavelength 598 nm (produced by a sodium lamp) traveling through air strikes a smooth, flat slab of crown glass at an angle of 30.0 degrees to the normal. Find the angle of refraction, r. Given: q1 = 30 degrees n1 = 1.00 n2 = 1.52 Unknown: q2 = ? Use the equation for Snell’s Law: Ni(sin i )= N r (sin r ) r = sin-1 [(ni / nr) (sin i)] = sin=1 [ (1.00 / 1.52) (sin 30 degrees)] r = 19.2 degrees
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