Refra ction By Bill Gracey

light slows down (v<c) Refraction- the bending of a light ray as it passes from one medium to another air glass light slows down (v<c)

http://128.148.60.98/physics/demopages/Demo/optics/demo/6a4210.htm

Transparent Light shines through; can clearly see through Translucent Partially transparent Opaque Rays of light can not pass through

Formula from wave Paper The Refractive Index (n) is a measure of by how much light slows down in a medium. Note nair/ vaccuum = 1.0 any medium n > 1 n has no units The speed of light in water is 2.29 x 108 ms-1. What is the refraction index of water? Formula from wave Paper

Light slows down when it enters a high density material from a low density medium. This causes the light to bend. Partial reflection Refraction 1 Refraction 2

Don’t forget to measure angles from The Normal n1 = initial medium n2 = final medium 1 = incident angle Don’t forget to measure angles from The Normal 2 = refracted angle

Bends away from the normal http://www.physics.brocku.ca/www/faculty/sternin/120/slides/LightOptics.html Bends toward the normal

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Concrete Sand Wood Carpet http://230nsc1.phy-astr.gsu.edu/hbase/sound/refrac.html#c1

Concrete (Fast) Grass (Slow) Mud (Very Slow)

 = angle to the normal (0) Snell’s Law n1sin1 = n2sin2  = angle to the normal (0) n = refractive index (no unit)

Notice: If n2>n1 : light ray bends toward the normal If n2<n1 : light ray bends away from the normal n1 sin 1 = n2 sin 2 Snell’s Law

Deriving Snell’s Law Consider two light rays. Velocities are v1 in medium 1 and v2 in med. 2. Medium 1 v1 v1t q1 q1 q1 R q2 q1 Segment R is common hypotenuse to two rgt. triangles. Verify shown angles from geometry. v2t q2 q2 v2 Medium 2

speed vacuum speed medium Snell's Law Index of Refraction = speed vacuum speed medium Willebrord van Roijen Snell 1580-1626 c v n = σ2 σ1 Air n1·sin(σ1) = n2·sin(σ2) Water nair·sin(σair) = nwater·sin(σwater) Water

Ex: air 60 water Find both the angle of reflection and the angle of refraction for this light ray incident upon water.

Your lecturer just drew the incorrect “refraction of light” sketch for light incident from air onto a blue glass plate, as shown below. What would you suggest to make it right? q1 q2 GLASS Make q2 smaller. State that as drawn, n2<n1. Curve the ray in the lower medium. Figure all angles from the perpendicular dotted line. None of the above.

The light exits the same glass plate shown in the previous sketch The light exits the same glass plate shown in the previous sketch. Select the direction that it will go when it exits the glass. A B C D E GLASS A B C D E

See 3 Snells law & TIR applet See 1 Snells law applet See 3 Snells law & TIR applet

AIM: To find out the refractive index of a block of plastic and or glass using Snell’s Law.

Light Box activity

Report expectations… Due Friday Experimental data sheet Can be shared with lab partner Data table Graph On Grid paper 2/3 size rule, labelled Line of Best fit Calculations Show clearly how you determined nglass & nplastic Questions answered