The Electromagnetic Spectrum

1
The Electromagnetic Spectrum

• Light has many different facets

2
Spectra of substances

• As we discussed earlier, the colors that we see
  in a spectrum actually reveal electron
  transitions in atoms.
• If we could calculate with certainty the energy
  associated with these specific colors, then it
  would be possible to measure the energy
  differences between these electron energy states
  directly.
• How can we do this?

3
Speed of Light

• Light is a wave (as discussed earlier)
• Waves have 2 characteristics wavelength and
  frequency
• One of the grandiose insights Einstein had when
  he was developing his theory of relativity was
  that the SPEED OF LIGHT IS A CONSTANT.
• C 3.00 X 108 m/s

4
Speed

• Since speed length / time
• Speed of light wavelength X frequency ?
  m ( 1/sec) ? m/sec
• Wavelength ? measured in m, nm, Å, µm
• Frequency ? measured in 1/s s-1 1/s 1
  hertz (hz)

5
Frequency

• To help us better understand frequency, go to
• http//www.howstuffworks.com/light2.htm

6
Speed of light

• C ??
• Speed of light wavelength X frequency
• Dim analysis m/s m(1/s)

7
Plancks Equation

• When Max Planck explained blackbody radiation, he
  developed an equation that equated the energy of
  a light particle with its frequency
• E hv
• Energy Plancks Constant X frequency

8
Plancks Equation

• E hv
• E Energy in joules (j)
• h Plancks Constant
• 6.626 X 10-34 Js
• v frequency in hz (1/s)
• Dim Analysis J Js (s-1)

9
We use these two equations to relate E, ?, and ?
of light

• E hv
• C ?v
• Sample Problem What is the frequency and energy
  of light at 532 nm?
• Solution worked on board.

10
The Electromagnetic Spectrum

• The electromagnetic spectrum is made up of
  several categories many o which you have heard
• Gamma rays, x-rays, uv rays, visible light,
  infrared light, microwaves, radio waves, TV
  waves.
• All of these types of radiation are classifies as
  light waves. Light make up more than just
  visible light (ROYGBV light)

11
Em applet

• http//lectureonline.cl.msu.edu/mmp/applist/Spect
  rum/s.htm

12
The Electromagnetic Spectrumpraxis.pha.jhu.edu/
pictures/emspec.gif
13
The Electromagnetic Spectrumhttp//www.yorku.ca/e
ye/spectrum.gif
14
Electromagnetic Spectrumhttp//www.geol.lsu.edu/h
enry/Geology7900/Cathodoluminescence/CLTheory-imag
es/VisibleLight-2.gif
E (j)
15
The Electromagnetic Spectrumhttp//www.lbl.gov/Mi
croWorlds/ALSTool/EMSpec/EMSpec2.html
16
Use these two equations

• E hv
• E energy (J)
• H Plancks Constant
• 6.626 X 10-34 Js
• V frequency (1/s s-1)

• C ??
• C spped of light
• 3.00 X 108 m/s
• ? wavelength (m, nm,
• µm, Å)
• V frequency (1/s s-1)

17
Related Sites

• http//imagine.gsfc.nasa.gov/docs/science/know_l1/
  emspectrum.html
• http//www.darvill.clara.net/emag/