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Name:  Casey
Status:  student
Age:  18
Location: N/A
Country: N/A
Date: 2000-2001


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?


Replies:
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


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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