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Photoelectrons and the work function

QUESTION: Photons of energy = 5.0 eV strike a metal whose Work Function = 3.5 eV. Find which one best describes the kinetic energy of the emitted [ejected] electrons?
Possible answers:
(a) 1.5 eV or less
(b) 1.5 eV or more
(c) 2.5 eV or more
(d) 3.5 eV or more
(e) 3.5 eV or less

Answer

There is no need to work out the frequency.

If the photons have an energy of 5.0 eV and the work function of the surface is 3.5 V it means that the maximum energy of the photoelectrons is 1.5 eV. 3.5 eV will be used in 'bringing' the free electrons to the surface of the metal leaving a maximum of 1.5 eV for kinetic energy.

It is a maximum because energy may also be liberated as heat.

The answer is (a)

 
 
 
© Keith Gibbs 2013