Physics Unit 3

Physics Unit 3

1. The Photoelectric Effect

   • Metal contains conduction free electrons. The electrons collide with each other and with positive ions of the metal.
   • If you shine a light of high enough frequency(UV) onto the surface of a metal, the metal will emit electrons.
     • Free electrons on the surface of the metal absorb energy (photons) from the light making them vibrate.
       • If an electron absorbs enough energy, the bonds holding the electron to the metal will break and the electron is released. (one electron absorbs one photon)
         • Therefore the higher the frequency of the electromagnetic radiation, the more energy the photons carry.
         • No photoelectrons emitted if below the threshold frequency
           • The number of photoelectrons emitted per second is proportional to the intensity of the radiation
           • maximum kinetic energy increases with the frequency of the radiation
       • A photon is a packet of energy.
         • energy of a photon: E = h x f
           • h = plancks constant
           • Photon energies are usually measured in electron volts (eV) 1 eV= 1.6 X 10-19J
   • Wave theory
     • emission should take place with waves of any frequency
     • emission would take longer using low intensity waves than using high intensity waves.