Refraction of Light

Review: Reflection Law of Reflection The angle of incidence equals the angle of reflection The incident and reflected rays lie in the same plane with the normal.

Refraction Sudden change in direction of a wave as it changes speed. It must enter obliquely to change direction! Which direction does it bend as it slows?

Refraction In both cases the speed of the wave has decreased. This is indicated by the decrease in wavelength!

Refraction In which medium does light travel faster? (glass rod appears bent)

Speed of light v is the speed of light in the new medium. c= 3.0 x 108 m/s Draw a graph for index vs. speed. What happens to speed of the refracted ray as it hits a medium with n < 1? How about n > 1? n is the absolute index of refraction. This is a measure of optical density. n is defined as the ratio of the speed of light in a vacuum to the speed of light in a new medium.

Relative Index of Refraction n is the relative index of refraction. If air is not used, then remember nrel = n2/n1 What is the relative index when going from diamond into lucite? If nrel < 1 ; speeds up If nrel > 1 ; slows down

Refraction n(water)=1.33; n(glass)=1.50; n(air)=1.00 Calculate the speed of light in water and glass. Vw = 2.26 x 108m/s Vg = 2.00 x 108m/s

Refraction n1- from n2 - into When a wave slows down it bends closer to the normal. {less to more – toward} n2>n1 When a wave speed up it bends away from the normal. {BLA – Big ―› Little – Away} n2<n1

Refraction If light rays bend closer to the normal when slowing down, why does the glass rod seem to bend away form the normal?

Apparent Depth Diverging rays enter your eyes. You “think” in Straight Lines. A virtual image appears to come from point y                    R – Real Depth A – Apparent Depth

Apparent Depth If the chest is 20 m below the surface at what depth will the image appear? Assume nsea water = 1.34

Snell’s Law n1sinθ1 = n2sin θ2 v1/v2 = λ1 / λ2

Example What is material X? Determine the angle of refraction. A monochromatic light ray f= 5.09 x 1014 Hz is incident on medium X at 55˚. The absolute index of refraction for material X is 1.66 What is material X? Determine the angle of refraction. Determine the speed of light in medium X.

Ex: Solution To find the angle of refraction use Snell’s Law. θ2= 30˚ The index of 1.66 is Flint Glass To find the angle of refraction use Snell’s Law. θ2= 30˚ To find the speed use n=c/v. v = 1.8 x 108 m/s

Dispersion The breaking up of white light into its component frequencies.

Refractive Index & Frequency The refractive index depends on the medium & the frequency of light. Each frequency “color” propagates at a different speed and bends a different amount.

Critical Angles Def: The angle of incidence when the angle of refraction is 90 degrees. When a light ray exceeds the critical angle it undergoes total internal reflection (TIR)

Snell’s Law Lab What factors effect the index of refraction of a liquid? Write up an experiment to test this question.