Spectroscopy for Pre-Schoolers

1. SpectroscopyforPre-Schoolers 2 October 2008 Jeff Hopkins Hopkins Phoenix Observatory (Counting Photons) Member of SAC

2. What is Light?

3. In 1865James Clerk Maxwell Said Where: The divergence of E (electric field) = 0 The divergence of B (magnetic field)= 0 The curl of E = -partial derivative of B with respect to time The curl of B = m0 x e0 x partial derivative of E with respect to time And There Was Light!

4. Maxwell’s Equations These equations quite elegantly describe the relationship between electric and magnetic fields and thus electromagnetic radiation. What these equations describe is the unit of electromagnetic radiation called a photon.

5. Photons Light consists of small packets of energy called photons. Photons have no rest mass and always travel at the speed of light, since they are light. Depending on how a photon is measured it will manifest itself as a particle or wave. The frequency or wavelength of photon is a function of it’s energy. The higher the energy, the higher the frequency (shorter the wavelength).

6. Wavelength (l For Light = c / f Where: l is the wavelength in meters c is the velocity of light, 299,792,458 meters/second and f is the frequency in Hertz (Hz) For light frequencies, wavelengths are given in nanometers (nm) or Angstroms (Å). 1 nm = 10 Å

7. Energy verse Intensity To keep things straight, the intensity of light is related to the number of photons and the energy of light is related to the frequency or wavelength of the photons. The brighter a color, the more photons involved. The higher the energy, the more toward the blue end of the spectrum the photon is (higher frequency, shorter wavelength).

8. Photon Energy Where do photons come from? Atoms consist of a nucleus surrounded by electrons. The electrons are in specific energy states or levels. If an electron is raised to a higher energy state it will soon fall back to its lower state and emit a photon of energy equal to the difference in the two energy states. Where: E = Photon Energy h = Planck’s Constant C = Speed of Light  = Wavelength E = h * c / l h = 6.62606896 x 10-34 J.s

9. Absorbing Energy A photon interacts with an orbital electron and raises it to a higher energy state. The electron absorbs the photon.

10. Emitting Energy After a short time the electron falls back to its lower energy state emitting a photon with the energy of the difference between the two energy states

11. Electromagnetic Spectrum The sensitivity of the human eye determines the visible spectrum and is typically 380 nm to 750 nm

12. What is Color?

13. Newton’s Experiment (1670) White light breaks up into colors Light colors combine to white light Single color does not change

14. RGB Photons Red, Green and Blue photons produce White for us to see.

15. There are no White Photons

16. Our Eye Our eye has sets of light cones that are sensitive to red, green and blue photons.

17. Color Color is an illusion! Different intensities of different energy photons striking our eye produce all the colors we see. Sometimes our eyes fools us greatly.

18. Our Experiment Each of you will have your own spectroscope so you can examine light. This is yours to keep. It is a scientific instrument so treat it well! Do Not take it apart! Slit Diffraction Grating

19. Your Spectroscope Do Not take it apart!

20. What You See Adjusting If needed, hold the slit end with the slit vertical and rotate the tube to see the above. The spectral lines should be on the right and left.

21. White Light

22. White You should see Red Green and Blue Lines There are no White photons or lines.

23. Red Photons

24. RedLight

25. Red You should see a Red Line

26. Green Photons

27. Green Light

28. Green You should see a Green Line

29. Blue Photons

30. Blue Light

31. Blue Light You should see a Blue Line

32. Yellow Light

33. Yellow You should see Red and Green Lines

34. COLOR ISANILLUSION

35. Red & GreenPhotons Red and Green photons produce Yellow for us to see.

36. Yellow Photons There are also Yellow photons as well as photons of every color.

37. Demonstration

38. Pickle Light A normal Pickle A normal Pickle with power applied. intense yellow sodium D lines light are emitted

39. Incandescent Light A continuous Spectrum

40. Fluorescent Light A Emission Spectrum

41. Pickle Light Spectrum You should see a Yellow Line

42. RGB Three basic colors of visible light are RGB. RGB stands for Red, Green and Blue Combinations of these colors with different intensities (number of photons) can produce all the colors we can see. RGB is an emission color set meaning color of the emitted light as opposed to reflected light. TV sets and computer monitors use emitted RGB light at different intensities to produce desired colors.

43. Why RGB While photons of the desired color could be used it would mean we would need to be able to generate millions of different colored photons for all the colors. Because our eye responds to RGB photons with the effect of letting us see any color by just varying the RGB intensities, we can generate all the colors with just the three RGB colored photons.

44. RGB(Single Colors) Red Green Blue

45. RGB(Combinations) 100% Green + 100% Blue = Cyan 100% Red + 100% Blue = Magenta 100% Red + 100% Green = Yellow

46. RGB(Extremes) 0% Red + 0% Green + 0% Blue = Black 100% Red + 100% Green + 100% Blue = White

47. Technicolor Colors seen on a movie screen, TV screen or computer monitor are the results of a combination of three basic colors, red, green and blue. Color film is a combination of three layers (RGB) combined to produce a full color image. We can produce a full color image by take monochrome pictures through a red, green and blue filter and then shinning white light through each and overlapping them.

48. Taking Monochrome Images

49. Three Monochrome Images Scene through Red Filter Scene through Green Filter Scene through Blue Filter

50. Red Filter Image