1. Light and the Electromagnetic Spectrum

2. WAVES AND MEDIUMS
What medium is light transferred through?
LIGHT DOES NOT NEED ONE!

3. Visible Light Spectrum

4. Light
Light is the form of energy visible to the human eye. This is “radiated by moving charged particles.”
*Source:

5. Visible light is the smallest part of the electromagnetic spectrum.

6. LIGHT
Light provides the energy need for both plant and animal life. The plants will then complete the process of photosynthesis.

7. LIGHT
The colors of the visible spectrum change depending on the wave frequency.

8. The higher the frequency the shorter the wave length is. (see chart)
LIGHT
The higher the frequency the shorter the wave length is. (see chart)

9. WAVELENGTH AND ENERGY OF THE VISIBLE SPECTRUM COLORS
Red
700 nm
1.771 eV
Reddish orange
650 nm
1.909 eV
Orange
600 nm
2.067 eV
Yellow
580 nm
2.138 eV
Yellowish green
550 nm
2.254 eV
Green
500 nm
2.480 eV
Blue
450 nm
2.765 eV
Violet
400 nm
3.100 eV
Source: Kurt Nassau, Experimenting with Color

10. It is no coincidence that this wavelength falls within the range of wavelengths at which the Sun emits most of its electromagnetic energy—our eyes have evolved to take greatest advantage of the available light.

11. Color
“Is a physical phenomenon of light or visual perception associated with the various wavelengths in the visible portion of the electromagnetic spectrum.”

12. COLOR
When looking at objects the object appears a certain color. This is the color that is being reflected off of the object, in reality, the object is every color but the color it appears to be.

13. COLOR
White light is made when the primary colors are added together “at equal intensities.”

14. When all wavelengths of light are being absorbed we see black (black also, isn’t really a color)

15. The colors we see in objects are the colors that are reflected, all other colors are absorbed. A red t-shirt appears red because red is reflected to our eyes and the other colors are absorbed.
When all colors are being reflected we see white light (white isn’t really a color)

16. Color Reflection So if we see something as WHITE, that means …
It reflected back all the wavelengths of light to our eyes
If we see something as RED or BLUE
It reflected only the RED or only the BLUE wavelengths
The others were absorbed.
And if we see something as black?
It did not reflect back any of the light.
© 2003 Mike Maloney

17. Primary Colors of Light
Red
Blue
Green

18. Colors of Light
These colors can be combined in different proportions to create all other colors.

19. Secondary Colors of Light
Red Light + Green Light = Yellow
Blue Light + Green Light = Cyan
Blue Light + Red Light = Magenta

20. Colors of the Spectrum Remember R-O-Y G. B-I-V? Red Orange Yellow
Green
Blue
Indigo
Violet

21. Visible Light
We know that the light waves enter our eye, and stimulate parts of it that cause a electrical impulse to be sent to the brain which creates this visual image.
But everything does not emit radiation. How do we see those things? And why cant we see a window?
© 2003 Mike Maloney

22. How Do Our Eyes See Color?
Two types of cells in the eyes:
Rods – Black and white
Cones – Color – 3 different types of cone cells
- Set 1 – Sees red
- Set 2 – Sees blue
- Set 3 – Sees green

23. Our Eyes
© 2003 Mike Maloney

24. LIGHT IS A WAVE! Since light is a wave, it will act like a wave!
Interference
Reflection – bounce back
Refraction – bending through a medium
Dispersion - scattering
Diffraction – bending to fit through
Polarization - concentration

25. Seeing things
We know that when waves run into a boundary they are partially transmitted and partially reflected.
Light behaves as a wave, so it to is reflected.
Therefore, an object does not need to emit photons itself to be seen, it just has to reflect light back to our eyes where we can detect it.
© 2003 Mike Maloney

26. Objects that do not allow light to pass through them are called opaque.
Objects that allow light to pass through them are considered transparent.
Objects in between are called translucent.

27. What is a Prism?

28. Prisms
A Prism is triangular object that separates white light into the spectrum colors.
The white light is bent once it enters the prism, and the prism bends the different wavelengths of the white light. Out come the colors of the spectrum.
The longer the wavelength (red) the less that it is bent, the shorter the wavelength (violet) the greater it is bent.
Prisms are used for many different things: Spectra Scopes and Binoculars.
Isaac Newton was the first to show that “When a second prism brings the different colors together again, white light is once more obtained.”
Source:

29. Polarization
Polarization is a phenomenon of light that is used in sun-glasses and 3-D movies.
Play with the two polarizing filters for a few minutes and note what is happening and see if you can think of any reasons for it.
© 2003 Mike Maloney

30. Polarization Hint Light vibrates in all directions.
A polarizing filter acts like a picket fence. It only lets certain direction vibrations pass through it.
Therefore, if you pass light through two of them you can completely block the light from passing through.
HOW?
© 2003 Mike Maloney

31. Polarization
© 2003 Mike Maloney

32. Color Transmission Filters work in a similar way.
Red filters only let RED light thru.
Blue let only BLUE light thru.
What do you think that UV sticker means on your sunglasses?
Why do they sell those orange glasses that are supposed to reduce glare?
© 2003 Mike Maloney

33. Station 1
Prisms

34. Station 2
What do your eyes see?
Reflected or Absorbed

35. Station 3
Seeing is believing

36. Station 4
Illusions

37. Station 5
The rose

38. Station 6
Color Wheel

39. Station 7
Venn Diagrams

40. Station 8
Polarized filters

41. Station 9
Transparent, Translucent, Opaque

42. Some Sweet Color Tricks
Combining colors in art class
How does color printing work?
Combining lights
Why is the sky blue?
Why are sunsets red?
Why is water greenish-blue?
How does 3-D work?
Why does a CD reflect a rainbow, and a mirror does not?
How can you help people who are color blind?
OTHERS  link to site
© 2003 Mike Maloney

43. BACK
© 2003 Mike Maloney

44. Illuminance
Flux is the total of all the light that is emitted from a source.
This is not very useful, often we would like to know how much of that light is hitting a surface at some point.
The illumination of a surface is called illuminance, E. It is measured in lumens per square meter, lm/m2
© 2003 Mike Maloney

45. Refraction and Reflection Telescopes
Refracting telescopes were the
first telescopes ever used. It is said
that two children invented this kind
of telescope, when they were playing
with two lenses. This was perfected
by Galileo. Isaac Newton created
the Reflecting Telescope.
Both telescopes work in the same
way. The difference is that
reflecting telescopes make better
use of mirrors instead of lenses.
Refraction Reflection
Source: The Universe

46. Hubble Telescope
The Hubble Space Telescope uses refection to portray images.
When light enters the telescope it is reflected off of large mirrors that are kept in static, dust free environments. Any dirt or dust present would ruin the images collected.
Then the light passes to a secondary mirror which reflects the light to the center of the primary mirror. At the focal point (where the light is focused into one point) the light is set to several different sensors which collect data based on that light.
Hubble Space Telescope's “mirrors are made of glass and coated with layers of pure aluminum (three-millionths of an inch thick) and magnesium fluoride (one-millionth of an inch thick) to make them reflect visible, infra-red and ultraviolet light.”
The mirror can weight almost 2000 pounds.
Source:

47. Examples of Visible Light
Source: The Universe, and

48. C = λν
The frequency (v) of a wave is the number of waves to cross a point in 1 second (units are Hertz – cycles/sec or sec-1)
λ is the wavelength- the distance from crest to crest on a wave

49. Why does this make sense?
The product of wavelength and frequency always equals the speed of light.
C = λν
Why does this make sense?
NOTE:
c is a constant value= 3.00 x 108 m/s

50. A certain frequency has to be achieved or the effect does not work
The photoelectric effect – When light shines on metals, electrons (photoelectrons) are ejected from their surface.
A certain frequency has to be achieved or the effect does not work
Red light will not cause electrons to eject!

51. The photoelectric effect has practical applications in photoelectrical cells used for solar powered cars, and solar powered calculators.