Light & Optics

Law of Reflection The angle of incidence of reflected light equals the angle of reflection.  r =  I Note that angles are measured relative to a normal to the mirror surface. shiny (+)dark (-) plane mirrorlight source incident ray normal reflected ray rr ii

Ray tracing: plane mirror Construct the image using two rays. +- object 5 cm Image -5 cm Reflected rays are diverging. Extend reflected rays behind mirror. Name the image: Virtual, upright, true size

Snell’s Law n 1 sin  1 = n 2 sin  2 n1n1 n2n2 11 angle of incidence 22 angle of refraction

n1 < n2 When the index of refraction increases, light bends toward the normal. n1n1 n2n2 11 22 When n 1 < n 2  1 >  2

n1 > n2 n1n1 n2n2 11 22 When the index of refraction decreases, light bends away from the normal. When n 1 > n 2  1 <  2

Problem Light enters an oil from the air at an angle of 50 o with the normal, and the refracted beam makes an angle of 33 o with the normal. a)Draw this situation. b)Calculate the index of refraction of the oil. c)Calculate the speed of light in the oil

Problem Light enters water from a layer of oil at an angle of 50 o with the normal. The oil has a refractive index of 1.65, and the water has a refractive index of a)Draw this situation. b)Calculate the angle of refraction. c)Calculate the speed of light in the oil, and in the water