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photoelectric effect

 Definition/Summary When a metal surface is irradiated, it ejects electrons whose kinetic energy can be measured. This electron emission only happens when the irradiating light is above a certain angular frequency $\omega_{0}$. This frequency threshold is found to be independent of the intensity of the radiation. The kinetic energy of the electrons is found to be linearly related to the frequency of light after the threshold, with $$T = \hbar(\omega - \omega_{0})$$

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 Scientists Einstein

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 Breakdown Physics > Quantum >> Applications

 Extended explanation In most elementary courses, the frequency of light is used instead of the angular frequency. The two are related by: $$\omega = 2\pi \nu$$ The photoelectric effect was important in realising the true nature of light. Classically light is a wave and as such the energy from it should arrive at a uniform rate. In this picture there would be no reason for the electron energy to depend on the frequency and be independent of intensity. This led Einstein to postulate that light was carried in little packets of energy called photons. The amount of energy needed to overcome the binding energy of the electron in the metal is called the work function ($\phi$). The work function is obviously the same amount of energy as carried by a photon of threshold frequency; $\phi = h\nu_0$. Thus the maximum energy an electron can gain from a photon of energy $E = h\nu$, is: $$T = h\nu - \phi = h (\nu - \nu_0)$$