Total Internal Reflection

Direction of Refraction

Waves bend towards the normal when going from fast to slow

 and

away from the normal when going from slow to fast

Total Internal Reflection

When refraction angle exceeds 90º from the normal the light does not cross the interface

Fiber optics

Total internal reflection causes light to reflect inside a solid glass/plastic tube

Atmospheric Refraction

Wave fronts of light travel faster in the hot air near the ground, thereby bending the rays of light upward

 Polarization

Polarization

If a rope is shaken up and down, a vertically polarized wave is produced.

If a rope is shaken from side to side, a horizontally polarized wave is produced

A vertically vibrating electron emits vertically polarized light.

A horizontally vibrating electron emits horizontally polarized light

Polarization

Polarization

Reflection of light from non-metallic surfaces results in polarization parallel to the surface  

Most glare is horizontally polarized 

Polarized Light and 3-D Viewing

A 3-D slide show uses polarizing filters. The left eye sees only polarized light from one projector; the right eye sees only polarized light from the other projector

Diffraction and Interference 

Wave Diffraction

Diffraction is the bending of a wavefronts as they pass the edge of an object

Huygens' Principle

Every point of a wavefront may be considered the source of secondary wavelets that spread out in all directions

Huygens' principle explains wave diffraction

Wavelength and Diffraction

Diffraction is greater when the wavelength is large compared to the size of the object or aperture

Checkpoint 1

Two light rays of different wavelength (one blue and one red) go through a small slit opening. For which one would you expect stronger diffraction?

Wavelength and Diffraction

Diffraction is greater when the wavelength is large compared to the size of the object or aperture

Long wavelength (> 100 m) radio waves diffract more from mountain tops, reducing shadow regions 

Short wavelength (< 100 m)

 radio  waves diffract less, casting shadow regions. 

f < 3 MHz (AM, VLF, LF, MF )

f > 3 MHz (FM, HF, VHF)

Diffraction Interference Pattern 

Wave Interference in 2D

Diffraction and Interference

Constructive Interference

Destructive Interference

Diffraction and Interference

Interference Patterns are Wavelength Dependent

IF                            THEN constructive interference 

IF                                           THEN  destructive interference

Where            is the difference in distance traveled between waves from different sources

and  m = 0,1, 2, 3, ... is an integer number

Checkpoint 2

By how much should a pair of monochromatic light rays differ in distance traveled to produce destructive interference?

Interference Pattern as a function of wavelength

http://www.vtorov.com/interf.htm

Double-Slit Interference

IF                                                 THEN constructive interference 

IF                                                 THEN  destructive interference

Double-Slit Interference

Multiple-Slit Interference

Diffraction Gratings

A multitude of closely spaced parallel slits makes up what is called a diffraction grating

a diffraction grating separates colors by interference

Interference From Thin Films

Interference From Thin Films

As the thickness of the soap layer changes, different different wavelengths of light are canceled

Interference From Thin Films

Two things to consider:

• Phase inverts if n2 > n1
• Wavelength changes as speed changes 

Checkpoint 3

What is the smallest thickness of a soap bubble that produce constructive interference for red light of 650 nm? Use n = 1.33 for soap and assume light rays travel perpendicular to the film

The End