Silicon, Circuits, and the Digital Revolution

Atomic Units of Energy

• In our study of electricity we measured energy in units of kW-hr (kilowatt-hour).
  
• In atomic physics and semiconductor physics, we find that the eV (electron-volt) is a convenient unit for measuring energy of photons and electrons.
• Relationship between kW-hr and eV; eV and joule?
  • A watt-second is also an acceptable unit for energy, having the same dimensions as kilowatt-hour. The watt-second is more commonly known as a joule (J).
  • A 1 kg (kilogram) mass held overhead has about 20 J of potential energy relative to the floor; that is, when it hits my toe, it will be carrying 20 J of kinetic energy.
  • The electron-volt is the change of energy experienced by an electron when it is relocated from one point to another, when the two points have a 1.0 V difference.
  • The electron-volt is a small quantity compared to the joule:
    1.0 eV = 1.60 x 10^-19 J

The Visible Spectrum

The Tech

Photon "color":   Wavelength:   Energy:   (nm) (eV) Blue 430 2.9 Yellow 530 2.3 Red 650 1.9

Comments, suggestions, or requests to ghw@udel.edu. "http://www.physics.udel.edu/~watson/scen103/colloq2000/excitedstates.html" Last updated April 14, 2000. © George Watson, Univ. of Delaware, 2000.