1. Chapter 34—Ray Optics Items covered in this chapter: Reflections
Refraction
Color Dispersion
Thin Lenses
New equations:
n1sin1 = n2sin2 (Snell’s Law for refraction)
(Thin Lens Equation)

2. Chapter 34—Ray Optics The ray (or particle) model of light.
Light rays travel in straight lines with a speed of v = c/n.
Light rays can cross.
A light ray travels forever unless it interacts with matter. A light ray then reflects and/or refracts. Within a material light can be either scattered or absorbed.
An object is a source of light rays (even if it’s not).
The eye sees by focusing a diverging bundle of rays.

3. Reflection Some definitions: Normal Line Angle of Incidence i
Angle of Reflection r i r
For reflection r = i 5

4. Reflection Irregular or Diffuse Reflection Vs. Regular or Specular
Generally, one gets diffuse reflection when irregularities in the reflecting surface are larger than the wavelength of visible light
Mt. Washington 6

5. More definitions: Si So
i = image distance
o = object distance

6. Sample Reflection Problem
You have a height of h. What is the shortest mirror on the wall in which you can see your full image? Also: where must the top of the mirror be hung?

7. n1 n2 Refraction 1 Index of Refraction c = speed of light in a vacuum
v = speed of light in the material in question 2 n2

8. It turns out that the index of refraction of a substance is slightly different depending upon the frequency of light passing through a substance.

9. Refraction 1 2
From experience, we know that when light travels from one medium to another, it’s path is bent. For example, we know that water “bends light”. 7

10. Refraction n1sin1=n2sin2 And we get Snell’s Law
Where v1 is the velocity
of light in medium1 and
v2 is the velocity of light
in medium2.
Now, the speed of light in a vacuum is
3*108 m/s. We don’t like dealing with such large numbers, so we give materials numbers in a range we can deal with…
And we get Snell’s Law
n1sin1=n2sin2 1 2
We define the Index of Refraction as: n = 8

11. Let’s take a look a closer look at Snell’s Law. n1sin1=n2sin2
Let’s try shining a light from the bottom of a swimming pool, up toward the surface.
In this case, n1=1.33 and n2=1.00
Thus, we have that sin2=1.33sin1
n2=1.00
n1=1.33 9

12. Thin Lens: A lens is considered thin when its thickness is small compared to all the other distances involved.
Two types of thin lenses:
Convex and Concave f f o i

13. Spherical Mirrors (Concave): Ray Tracing Method:
Ray 1: This ray is initially parallel to the principal axis. It passes through the focal point F after reflection from the mirror.
Ray 2: This ray passes through the focal point F and is reflected back parallel to the principal axis.
Ray 3: This ray travels along a line that passes through the center of curvature C and follows a radius of the spherical mirror. (i.e. it reflects back on itself)

14. Spherical Mirrors (Concave):
Mirror Equations:

15. Focal length
f is + for a concave mirror
f is – for a convex mirror
Object distance
o is + if the object is in front of the mirror (real)
o is – if the object is behind the mirror (virtual)
Image distance
i is + if image is in front of the mirror (real)
i is – if image is behind the mirror (virtual)
Magnification
m is + if image is upright
m is – if image is inverted

16. f f o i

17. 0) We look at the light rays coming from the top of the object.
Ray 1 goes parallel to the axis of symmetry until you get to the middle of the lens. At the middle of the lens, you then draw a straight line that goes through the opposite focal point of the lens.
Ray 2 goes straight through the middle of the lens and is not distorted.
Ray 3 goes through the near focus, until it gets to the middle of the lens. From the middle of the lens, the ray continues in a direction parallel to the axis of symmetry.

18. Formation of a virtual image through a converging lens.

19. The Thin Lens Equation:f f s s’

20. Note what happens when the object is far away:

22. For a telescope, due to diffraction, the best angular resolution that can be seen by the telescope is:

23. Topics in Chp 34 that will be in the exam: Remembered that the index of refraction is defined n = c/v Snell’s Law: n1sin1 = n2sin2 Ray Tracing Converging and Diverging Lenses We used the Thin-Lens Equation to calculate the position of the image and the magnification. Maybe you’ll need to be able to use the “spherical lens equation” or “lens maker equation”.