Physics Section 14-1 Refraction

Refraction Recall that when a wave front moves at an angle into a medium of a different density, the wave front will bend and the speed will change. Since the frequency of the wave remains the same, the wavelength will also change.

Examples of light refraction

Snell’s Law n1 sinθ1 = n2 sinθ2 Thomas Harriot, René Descartes, and Willebrord Snellius (Snel van Royen) all studied the bending of light and derived a law relating the angle of incidence to the angle of refraction in the early 1600s. The law is named after Snellius. n1 sinθ1 = n2 sinθ2 Snell’s Law n is the index of refraction and is found by comparing a substance to a complete vacuum. Some values for n vacuum – 1.00 ethanol – 1.36 quartz – 1.54 air – 1.0003 Plexiglass – 1.49 flint glass – 1.62 water – 1.33 crown glass – 1.52 diamond – 2.42

When light goes from a lower to a higher index of refraction, the ray bends toward the normal. v1 faster medium v2 slower medium n2 > n1 v2 < v1 θ2 < θ1 When light goes from a higher to a lower index of refraction, the ray bends away from the normal. n2 < n1 v2 > v1 θ2 > θ1

Speed ratios The index of refraction is related to the ratio of the speed of light in a medium compared to the speed of light in a vacuum. Since θ decreases as speed decreases, and since the higher the index of refraction the smaller the angle and speed (ie. inverse), we can say, n2 v1 = n1 v2 If we let medium 1 be a vacuum (n = 1.0), then, c n c = speed of light in a vacuum = v c = 3.00 × 108 m/s