Nature of Light

Notes i got from Nature of light. 

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  • Created by: John D
  • Created on: 19-04-12 20:51

Photoelectric emission

Photon - Packet of electromagnetic energy. 

When a single photon is absorbed by a metal surface engery is transfered to an elctron which may be given off and its called a photelectron, this process is called photelectric emmission. 

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The Work Function

The minimum amount of engery required to release an electron from a metal surface is called the work function. 

For photoelctric emmision the energy of the photon has to be greater than or equal to the work function. 

If the the photons energy is enough to release an electron the frequency is called the threshold frequency.

E=hf=work function 

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Energy Conversion

If the energy of a photon is greater than the work function then the photoelectron can aquire kinetic energy. 

work done in releasing the electron + kinetic energy of electron = photon energy

Photoelectrons may have less than the maximum kinetic energy if they transfer energy to the metal on their way to the surface.

If the photon energy is less than the work function, the energy absorbed by the metal just causes a slight amount of heating.

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The wave model and the photon model

Under certain conditions light diffracts. Diffraction can only be explaned if light is a wave. 

In the photoelectric effect predicts that low energy would give off a lot of electrons.This isnt true.  

Light is also a photon, this explains the photoelctric effect. weak radiation causes instantaneous release of some electronsif the frequency is greater than the threshold frequency. 

KE only depends on frequency and not intensity 

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Stopping Voltage

Battery pos-neg. Electrons will want to escape and move to positve end of wire. 

reverse battery electrons don't want to leave. 

Stopping voltage is the amount of voltage needed to stop current. It depends only on frequency. 

Kmax = eVs

In graph it begins at zero until it reaches threshold frequency then it increases linearly. 

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