REFRACTION OF LIGHT

Refraction is the bending of light as it enters a new medium. If the new substance is more optically dense the ray bends toward the normal If its less dense the ray bends away from the normal.

Water is Water is Light moves More dense less dense along normal Oil air air water glass water Bends away from the normal. Speeds up Moves along normal line. Slows down. Bends toward the normal. Slows down.

Incident angle and refraction angle are measured from the normal line.

Absolute Index of refraction Ratio of the speed of light in a vacuum to the speed of light in the new medium. Values can be found on the reference table or calculated using: n = c / v C = speed of light (m/s) V = speed in new medium n = index of refraction (no units)

Sample problem What is the speed of light as it travels through a bottle of corn oil? (neglect the plastic container) n=c/v 1.47= 3 x 108m/s V V = 2.04 x 108m/s

Snell’s Law ALSO: n2 / n1 = v1 / v2 = λ1 / λ2 Relates the angle of incidence and angle of refraction to the corresponding indices of refraction. (incident) (refracted) n1sinθ1 = n2sinθ2 ALSO: n2 / n1 = v1 / v2 = λ1 / λ2

SNELL’S LAW AIR LUCITE

Sample problem n1sinθ1 = n2sinθ2 Colored light in air is incident on a sample of lucite at an angle of 37˚. a) What is the angle of refraction? n1sinθ1 = n2sinθ2 1.0 sin 37 = 1.50 sin θ2 0.6018 =1.50 sin θ2 1.50 1.50 sin θ2 = .4012 θ2 = 23.7˚

b) What is the velocity of the refracted ray? n2 / n1 = v1 / v2 1.5 = 3x108m/s 1 V2 v2 = 2.0 x 108m/s

c) If the light has a wavelength of 4.8 x 10-7m in air, what is its wavelength in lucite? n2 / n1 = λ1 / λ2 1.5 = 4.8 x 10-7m 1.0 λ2 λ2 = 3.2 x10-7m

d) What is the frequency and color of the light? (Use the value for air.) v = f λ 3x108m/s = f (4.8 x10-7m) f = 6.25 x 1014Hz its blue light

CRITICAL ANGLE The incident angle that will cause the light ray to have a refracted angle of 90 degrees glass glass glass air air air Incident angle is smaller than the critical angle Incident angle is equal to the critical angle Incident angle is larger than the critical angle

CRITICAL ANGLE SIN θc = 1/n n-index of refraction θc- critical angle ex: What is the critical angle for lucite? sin θc = 1/1.50 = 0.66 θc = 41.81˚

Refracted light waves