Man tossing hot and cold water balloons
(thermal infrared!)

School Blocks YouTube? Click on video link below





B) Einstein explains photoelectric effect



1) Light intensity and electron emission explained.



Photons are received individually
Each photon emits e -  



Light emitted as particles
(quanta of light - photon)



Bright Light



 Dim Light

(Lots of photons)

 (few photons)





High Frequency Light

Low Frequency Light

(High Energy Photons)

(Low Energy Photons)





Brightness (Intensity) - measure of # of photons emitted.



Frequency measure of energy of light

Photon Energy = 5 eV

KE = 2 eV




**eV - electron volts - unit of energy






How much work did this photon have to do to remove the electron? 




Answer: 3 eV






What would happen if a photon
 of 2 eV hit the same metal?


Photon Energy = 5 eV KE = 2 eV





Photon would not have enough energy to emit an electron

Photon Energy = 5 eV KE = 2 eV





Emax = hf - Wo


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