1. Light Waves
What we call light is a small portion of the electromagnetic spectrum
All the different colors are electromagnetic waves with different wave lengths
Wave speed = frequency x wavelength
EM radiation is alternating electric and magnetic fields

2. EM Spectrum
long 
low f
low energy
short 
high f
high energy

3. Electromagnetic Waves
Changing magnetic/electric field induces electric/magnetic field

4. Electromagnetic Spectrum
Remember, the lower the frequency the longer the wavelength and vice versa
Wave speed of light is 300,000,000 m/s

5. Visible Light Visible Light small part of the spectrum we can see
ROY G. BIV - colors in order of increasing energy R O Y G. B I V
red
orange
yellow
green
blue
indigo
violet

6. Colors Lowest frequencies of visible light are red
Highest frequencies are violet
The order is red, orange, yellow, green, blue, indigo, violet

7. Colors
Colored objects are a result of selective reflection and absorption of light
Sunlight is a mixture of colors
We call this mixture white light
When white light strikes a red object, the red frequencies are reflected and the other frequencies are absorbed

8. Sunlight

9. Colors White objects reflect all frequencies
Black objects absorb all frequencies
Objects can only reflect the colors of light that shine on them
If you shine blue light on a red object it will look black

10. Colors
We can also consider shining light through semi-transparent objects
Filters used on the lights in a theater are materials that absorb some frequencies and let other frequencies pass through
Red filters transmit red light through the material while other frequencies are absorbed

11. Mixing Colors
Our eyes and brains are very complicated color processing sensors and computers
Artists have learned how to mix colors to make pleasing combinations and to create a huge array of different colors
All based on what the sensors in our eyes respond to

12. Visual Response

13. Mixing Colors Primary light colors red, green, blue additive colors
combine to form white light
EX: computer RGBs

14. Mixing Colors
Filter
transparent material that absorbs all light colors except the filter color

15. Mixing Colors Pigment Primary pigment colors
colored material that absorbs and reflects different colors
Primary pigment colors
cyan, magenta, yellow
subtractive colors
combine to form black
EX: color ink cartridges

16. Mixing Colors Light Pigment
When mixing pigments, the color of the mixture is the color of light that both pigments reflect.

17. Light and Matter Opaque Transparent Translucent
absorbs or reflects all light
Transparent
allows light to pass through completely
Translucent
allows some light to pass through

18. Selective Scattering This is why the sky is blue!
The higher frequencies are scattered more by the molecules in the atmosphere
Reds and oranges just pass through, so the sky appears blue

19. Blue Sky & Red Sunsets Molecules in atmosphere scatter light rays.
NOON
less atmosphere
less scattering
blue sky, yellow sun
Shorter wavelengths (blue, violet) are scattered more easily.
SUNSET
more atmosphere
more scattering
orange-red sky & sun

20. Diffraction Waves bend when they encounter an object
Stand in the water and watch the wake from a boat hit you
Look behind you and you will see that after a short distance, the wake continues on
It filled in the hole by bending around you
This bending is called diffraction

21. Diffraction Diffraction bending of waves around a barrier
longer wavelengths (red) bend more - opposite of refraction

22. Diffraction Diffraction is the third way to bend light
The other two are reflection and refraction
The amount of bending that occurs depends on the relative sizes of the object and the wavelength of the wave
Longer wavelengths bend easier than short ones

23. Diffraction

24. Interference Interference constructive  brighter light
destructive  dimmer light

25. Interference
When the waves are hitting the edges of something, the new bending waves tend to interfere with each other and we get some new patterns
Recall the principle of superposition
We simply add the amplitudes

26. Interference

27. Interference
Wave nature of light was demonstrated by Young

28. Interference
The bright and dark areas result from differences in path lengths from the slits to the screen
This changes the where the peaks and troughs appear
Remember the principle of superposition

29. Interference

30. Interference

31. Interference Can get interference from a single slit
Waves coming through one side of the slit interfere with waves coming through the other side
Extend the idea to three, four… slits
Make something with hundreds of slits
Called a diffraction grating

32. Diffraction Gratings
Used in spectrometers (devices to separate light into colors
It spreads the spectrum
Since different colors have different wavelengths, the constructive interference occurs at different locations

33. Diffraction Gratings

34. Diffraction Gratings
glass or plastic made up of many tiny parallel slits
may also be reflective
spectroscopes, reflective rainbow stickers, CD surfaces

35. Thin Films Look at an oil slick floating on the surface of a pond
The slick has a rainbow of colors depending on the angle of viewing
This results from interference in the very thin film of oil
Called iridescence

36. Thin Films

37. Thin Films - Bubbles & Oil Slicks
interference results from double reflection

38. Polarization
A phenomenon that occurs in transverse waves only

39. Polarization These waves are plane-polarized
All the motion is confined to a plane

40. Polarization
Shake an electron up and down and you create an electromagnetic wave that is plane-polarized in the vertical direction
Shake an electron side-to-side and you create an EM wave that is plane-polarized in the horizontal direction

41. Polarization
A standard incandescent bulb emits light that is unpolarized
The electrons are shaking in random directions
So, the light has its electric field shaking in different directions for different waves

42. Polarization

43. Polarization
Some transparent crystalline materials have a remarkable property
These materials have their atoms arranged in non-cubic structures
These crystals effectively divide the light into two beams that are plane-polarized at right angles to each other

44. Polarization
Any polarization direction can be split into a horizontal and vertical component. Like adding two separate beams together.

45. Polarization
Some crystals strongly absorb one of these beams while letting the other beam pass right through
These materials are called polarizers
Take a thin sheet of such a material and imbed it between two sheets of glass or cellulose, and you have a Polaroid filter

46. Polarization

47. Polarization What happens if we work with two polarizers?
If we place them so they are aligned, then the light passing through the first polarizer, will also pass through the second one
But if the polarizers are at right angles, the second one will absorb all the light

48. Polarization

49. Polarization
Most of the light reflected from non-metallic surfaces becomes polarized
Consider the glare from glass or water
Reflected wave has more vibrations parallel to the surface
Analogous to skipping a rock across a pond

50. Polarization
Sunglasses are polarized to block rays reflecting from horizontal surfaces light the road or a lake
This means the direction of polarization of the sunglasses is vertical so it blocks horizontally polarized rays

51. Polarization