1 EM wave spectrum Low photon energy High f Low f Long short High photon energy 1 photon has Photon Energy = hf = h c/ n photon has Photon Energy = n hf Intensity of Light (1) (2) More photons, higher Intensity UVX-raygamma-rayIR Micro wave Radio wave Visible ray

2 Photo-electronic Effect Let a story to explain this effect: How “Photon” Rescues Miss “Electron” _____ Electrons are trapped inside the metal-X No Electron is released !!! metal-X Cage Yellow Photons

3 One Green Photon releases one “Electron”, but vel=0 Electrons are trapped inside the metal-X ____ _ V=0 Electron is motionless Photon energy E just has sufficient energy to release Electron, but no extra energy for Electron so K.E=0 Frequency of green is called threshold frequency f 0 Green Photon

4 frequency of Green Photon = f 0 for metal x Incident Photon Energy E Green = hf where K.E= 0 Rewritten as : hf Green = hf 0 f Green = f 0 i.e. f Green is the “threshold frequency f 0 ” of metal X hf 0 =   is called work function Work function (  ) is the amount of energy to release electron for this metal-x

5 One Violet Photon gives K.E to released “Electron” Electrons are trapped inside the metal-X ____ Electron gains K.E She flies Violet Photon Blue, violet or photon with higher f

6 Higher frequency photon f>f 0, gives K.E Incident photon energy (E  = hf ) is higher than work function Or f>f 0 The expression can be written as

7 Conclusion 1. Electron to be released is dependent on frequency or wavelength of Photon NOT the number of photon (or intensity). 2.The min. frequency of photon to be released the electron is called threshold frequency (f 0 ) which does not give K.E to the electron. i.e in this example, green is the threshold frequency for metal X 3. Higher frequency of 1 photon as f>f 0, will give release 1 electron with K.E incident light: E = hf 0 +K.E Rewrite hf =  +K.E where  =hf 0 = work function