photoelectric effect

• Photoelectric emission


  Emission of electrons from the surface of a metal when electromagnetic radiation of sufficiently high frequency falls on it
• Work function Ø


  Minimum quantity of energy needed to liberate electrons from the surface of a metal and to just allow it to escape to an infinite distance from the metal
• Threshold frequency f0


  Minimum frequency needed to liberate electrons from the surface of a metal and to just allow it to escape to an infinite distance from the metal
• An electron at an infinite separation from the nucleus is considered to have zero energy
• The energy of the electrons in the bound states (orbits) must therefore have negative energy since they have to receive energy to escape the atom
• Ground state


  Lowest energy level an electron can occupy and is the most stable
• Metastable state


  One in which an electron stays much longer compared to a normal excited state
• Population inversion


  When there are more electrons in the metastable (excited) state than in the ground state
• Stimulated emission


  When an incident photon which has the same energy as the gap between the metastable and ground states stimulates all the electrons to relax down to the ground state at the same time with the same phase and in the same direction