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)

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

 = 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

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

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

Find nwater, nglass, ndiamond If V not know - find n using Snells law n1sin1 = n2sin2

A refractometer is a device that measures the refractive index of a liquid. This can be used to calculate the concentration of the liquid. Bile concentration is calculated using a refactometer (see image 3&4). Kiwi fruit are picked when the refractive index indicates that sugar levels are correct (see image 5).

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