1. Refra
ction
By Bill Gracey

3. 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)

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

7. 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

8. 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

9. 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

10. Bends away from the normal
Bends toward the normal

12. Concrete Sand Wood Carpet

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

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

16. 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

17. 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

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

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

20. 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.

21. 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

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

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

24. Light Box activity

26. 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