Ask A Scientist© Physics Archive

name         Casey
status       student
age          18

Question -   Details of the photo-electric effect.
I know the general principal behind the photo-electric effect.  I
know that when a photon hits an atom, it excites the electrons, and if
the photon has enough eV it will knock the electron out of its
orbital.  From Eintein's nobel prize, I know that there is a certain
level at which the electrons in an atom are unleashed and can be
detected.  The question I need to be answered is if the electron is only
unleashed when the work function is a certain eV, how do you determine
the range of wavelengths(longest and shortest of the light that is
bombarding a certain material)needed to emit electrons?

The light impinging on the metal sample must have more energy than the work
function of the material.  The energy of a photon is determined by its
frequency according to the formula
   E = h nu
where E is the energy of the photon, h is Planck's constant, and nu is the
frequency of the photon.  The wavelength is determined by the frequency by
the formula
   lambda = c / nu,
where c is the speed of light and lambda is the wavelength.

This means that a photon with short wavelength has more energy than a photon
with a long wavelength.  To cause a material to eject an electron, the
photon must have a wavelength shorter than the one corresponding to an
energy equal to the work function.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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Light is composed of a set of "photons".  Each photon carries light energy
proportional to the frequency of the light: E=hf/(2*pi).  The value of the
constant h is 4.14x10^-15 eVs.  It is called Planck's constant.  An
individual photon must have enough energy to free the electron.

Kenneth Mellendorf
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