1. Chapter 18: Refraction and Lenses
Pre-Class for Tuesday
In terms of light transmission, what is the difference between mirrors and lenses?

2. Refraction
Definition: bending of light as it passes from one material to another
Cause: light travels slower through more optically dense materials
The optical density is measured by the index of refraction (n), which is the ratio of the speed of light in a vacuum (c) to the speed of light in that material (v)
n = c / v

3. n1sinq1 = n2sinq2 Snell’s Law
Describes how light behaves when passing from one material to another
Light passes through an object, but is deflected off its original line
Amount of refraction is based on the object’s optical density and incident angle
Incident ray
Normal
Refracted ray
n1sinq1 = n2sinq2

4. Total Internal Reflection
Light attempts to pass from one material to another
Light must be traveling from a more dense to a less dense material
If the incident angle is larger than the critical angle (qc), then light is reflected
Law of Reflection applies (qi=qr)
sin qc = n2/n1

5. Pre-Class Wednesday 4-11-12
What causes a rainbow?

6. 3 TYPES OF LENSES PLANE CONVEX CONCAVE flat lens (window)
always gives a real image
CONVEX
curved towards the object (symmetric on both sides)
gives virtual or real images
CONCAVE
curved away from object (symmetric on both sides)

7. 1/f = 1/di + 1/do LENS EQUATION f : focal length
di : distance to image from lens
do : distance to object from lens

8. M = hi / ho = - di / do MAGNIFICATION M : magnification
hi : height of image
ho : height of object
di : distance from image to lens
do : distance from object to lens

9. S I G N S If di is negative, virtual image
This Way
If di is negative, virtual image
If di is positive, real image
If M is negative, inverted image
If M is positive, upright image
rule of thumb: real images are what we expect, so they are positive (light passes through lens)
remember: just because M is negative does not mean it is smaller, the sign is for orientation only
F=m a
No, this way

10. Ray Diagrams for Lenses
// OA, thru f1
Thru f2, then // OA
Thru center of lens
Note: use refraction line and not actual lens surface.

11. HW CH 18
; water
o; 28.9o
x108 m/s o
73. 53o, shallower
x108 m/s; 1.99x108 m/s
78. 28o; 32o; 53o cm cm cm cm
mm, do is infinity
mm, -5, -20 mm, -10
cm, cm, inverted; -324 cm, -40 cm, inverted; -4 mm

12. Pre-Class Thursday
Which color of light travels the slowest through a material?
Red
Green
Yellow
Violet

13. Optical Devices

15. Ch19: Interference and Diffraction
Diffraction is the scattering of light from a surface.
Incoherent light: light that travels in all directions with circular wavefronts
Coherent light: light that travels in one direction with linear wavefronts
Sunlight or light bulb
Laser or collimated beam

16. One piece of paper per group. Be sure everyone’s name is on it.
Practice Problems
Complete the following four:
p487 #1-4
Choose three of following:
p496 #15-17
p497 #20-23
One piece of paper per group.
Be sure everyone’s name is on it.

17. Lenses Activity
For each person, find the position for each lens that produces a sharp, clear image.
Repeat for 2 lenses together
Your name
Type of lens
Lens to eye M
Upright or inverted
both
Lens to lens

18. Pre-Class Wednesday 4-15-09
What type of lens is in your eye?
Hint: there are only three possibilities.

19. What is the smallest value that the index of refraction can be?
Pre-Class Thursday
What is the smallest value that the index of refraction can be?

20. LENS LAB Materials: Objective: Procedures:
meter stick, optical bench kit, lenses
Objective:
Find the focal length for each lens
Procedures:
Fill-out the chart on the next slide
Draw ray diagrams for each different lens
Repeat step 1 as time allows for a different lens

21. FILL-IN CHART
NOTE: Be sure image is sharp and clear. Look for it on the correct side (real or virtual image).