Physics AQA a as unit 1 Photoelectricity

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PhotoElectricity

photoelectricity is when light of a high enough frequency is shone on a metal electrons are released from the surface of the metal

The photoelectric effect occurs when matter emits electrons upon absorbing electromagnetic energy. (http://0.tqn.com/d/chemistry/1/G/7/z/photoelectric_effect.jpg)

intensity of light does not effect the number of electrons released

this proves that light can act as an particle as 

- one electron absorbs one photon

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PhotoElectricity

Einsteins explanation for photoelectricity

einstein assumed that light is made up of wavepackets known as photons

each of energy that is equal to hf

plancks constant x frequency of the light

when light is incident on a metal an electronat the surface absorbs a single photon and therefore gains energy equal to hf

an electron can leave the metal surface if the energy gained by the photon exceeds the work function of the metal 

work function is the min energy needed for the electron to escape from the metal surface

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equatins

Threshold frequency is min frequency needed for the electron  to escape

work funtion is the min energy needed for the electron to escape

equations

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Graph

on a graph 

Gradient = h 

y intercept = work function

x intercept = threshold frequency

Y axis is the energy 



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photoelectrons

Photoelectrons are emitted with a range of KE  This is because electrons can be found near the surface of the cell and deep down at the bottom of the metal if an electron is near the surface then it requires less energy to be released than an electron at the bottom would , therefore electrons released have a range of kinetic energies

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Electron collisions and ionisation

When an electron is excited it absorbs an photon however the photon does not have enough energy to leave the metal 

so ke is lost due to collisions

in ionisation a photon is absorbed which has enough energy for the electron to be able to leave the metal

Electron volt is (1.6 x10-19) x 1 v

Excitation of electrons can also occur by collisions between electrons 

de excite to release photons of light

excitation can also occur by absorption of photons

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