1. 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)

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

3. 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

4. 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

5. 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

6. Bends away from the normal
Bends toward the normal

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

9. 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

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

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

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

13. 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).

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

15. Light Box activity

17. 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