PHYSICS NEW ONE --------------

Folie 1

• PE effect=explained by Einstein's Photon model of light.
• Einstein suggested that EM waves and their energy exist in discrete packets : PHOTONS.
• -The energy carried by one of these photons is: E=hf=hc/la
• h=planck's constant 6.63x10-34
• c= SOL 3.00x108
• Einstein saw these photons of light as having a ONE-ONE-ONE , PARTICLE-LIKE interaction with an electron in a metal surface.
• A photon would transfer all its energy to ONE, SPECIFIC ELECTRON.
• Acc to the Photon model:
• -When light hits its surface, the metal is bombarded by photons.
• -If one of these photons collides with a free electron, the electron will gain energy equal to hf.
• Before an electron can leave the surface of the metal, it needs enough energy to break the bonds holding it there. This energy is called the work function (Phi symbol) and its value depends on the metal.
• PHOTOELECTRIC EFFECT
• The photon model explains the threshold frequency
• If the energy gained by an electron (on the surface of the metal) from a photon is GREATER than the WORK FUNCTION, the electron is emitted.
• if it isn't, the metal will heat up, but NO ELECTRONS will be emitted.
• Since, for electrons to be released, hf has to be greater than or equal to the work function, the threshold frequency must be:
• f=work Func/h

Folie 2

• THE PHOTON MODEL EXPLAINS THE MAXIMUM KINETIC ENERGY
• The energy transferred to an electron is hf
• the kinetic energy the electron will be carrying when it leaves the metal is hf MINUS any energy it's lost on the surface. Electrons deeper down in the metal lose more energy than electrons on the surface, which explains the range of energies.