1. Speed of light Galileo – “Its fast”
Roemer (~1700) – Period of Jupiter’s moon
“Its fast, but finite”
Michelson ( ) – First experimental measurement of the speed of light.

2. Speed of light in materials
For free space (vacuum) we showed
We expect in any other material

3. Speed of light in materials (dielectrics)
For a dielectric material we showed
We observe

4. Index of refraction
We will see later that n varies with frequency of light

5. Ray model of light Incident Ray Reflected Ray ni nt Transmitted Ray
Rays are a construct to show
the direction the wave is traveling
Transmitted Ray
Rays are generally perpendicular
to the surfaces of equal phase (wave fronts).

6. The Laws that are Empirically Observed
Law of reflection.
Snell’s Law of Refraction.

7. Reflection Definitions
External
Internal
Specular - Reflection off a smooth surface
Diffuse - Reflection off a rough surface
e.g. air to glass
e.g. glass to air

8. Plane Mirrors
The image is the same size as the object
Virtual Image

9. How big does your bathroom mirror have to be?
Shift your observation point to a top view and observe the right-left inversion of an image in a plane mirror.

10. Corner Reflectors
The reflected light ray is always parallel to the incident ray.
Implication for stealth technology.

11. A More Physical View of the Law of ReflectionB C ni nt A D

12. A More Physical View of the Law of ReflectionB C ni nt A D

13. Paraxial rays

14. Refraction
The bending of a light ray at the boundary between two media.
Snell’s Law:

15. Refraction Basics
Incident, reflected, and refracted rays are all in the plane of incidence.
A ray entering a higher index medium bends toward the normal.
A ray entering a lower index medium bends away from the normal.
Relative index of refraction
Vacuum wavelength

16. Example
A light ray is incident on a water surface at an angle of 30 degrees w.r.t. the normal to the surface. What is the angle of the refracted ray relative to the normal to the surface?
Does the frequency of the light change at the water boundary?
Does the wave length change in the water?
How much?

17. Fermat’s Principle
The actual path between two points taken by a beam of light is the one that is traversed in the least time. S h ni O x nt b P
a-x a

18. Total Internal Reflection
There will always be an angle such that
(even though it can’t be physically)
We define a critical angle for the limiting case:

19. Fiberoptics nc ni nf
How big can be?

20. Fiberoptics nc ni nf
How big can be?

21. Dispersion Difference in wave speed (n) in a material due to frequency
(or wavelength)