Monday, August 25, 2008


The phenomenon of ejection of electrons from the surface of some metals like Cs, K and Rb when light of a certain frequency strikes on it is called photoelectric effect. The emitted electrons are called photoelectrons.
Metals having very low ionization energies exhibit photoelectric effect with visible light. Other metals show this effect with more energetic radiations such as U.V light.

. Photoelectric effect is instantaneous.
· For each metal, there is a characteristic minimum frequency called the threshold frequency below which the photoelectric effect does not occur.
· The kinetic energy of the ejected electron is proportional to the frequency of incident radiation and is independent of its intensity.

If hu is the energy of the striking photon and hu0 is the minimum energy required to eject an electron then the excess energy hu-hu0 is transformed to the photo electron as kinetic energy, 1/2mv2 where m is the mass of electron and v is the velocity. Thus,
hu-hu0 = ½ mv2 = K.E of electron.
This is the Einstein’s photoelectric equation.

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