Photoelectric Effect

Photoelectric Effect

1. Scientific Basis

   • Emission of electrons from the surface of the metal when light falls on a cold metal surface (due to photons)

2. Einstein explanation of the photoelectric phenomenon

   • 1)Photons falls on a metalic surface with E=hv
   • 2)Work Function (Ew): It's the least energy needed to free electrons from the surface of a metal
     • Ew= hVc
   • 3) If (Vc) is the smallest frequency of the light required to let the electrons be free therefore
     • If hν< Ew
       • No electrons would be emitted
     • If hν= Ew
       • Electron is barely able to be free but without gaining KE
     • If hν < Ew
       • Electron is freed with gaining KE
         • KE = hν - Ew = ½ mv²
   • 4)The emission is instantaneous there is no need for time to collect energy IT TAKES PLACE ONCE hν > Ew

3. CLassical theory FAILED to explain the photoelectric effect

   • 1- Photoelectrons depends on radiation intensity not frequency (ν)
   • 2- KE Depends on radiation intensity
   • 3- low radiation intensity will emit electrons if given sufficient time regardless the frequency (ν)

4. Modern physics SUCCESS to explain the photoelectric Effect

   • 1-Photoelectric effect depends on frequency primarily
   • 2- KE Depends on Frequency (ν)
   • 3- Electrons are emitted instantenously