Early Photoelectric Effect Data

Electrons ejected from a sodium metal surface were measured as an electric current. Finding the opposing voltage it took to stop all the electrons gave a measure of the maximum kinetic energy of the electrons in electron volts.

The minimum energy required to eject an electron from the surface is called the photoelectric work function. The threshold for this element corresponds to a wavelength of 683 nm. Using this wavelength in the Planck relationship gives a photon energy of 1.82 eV.

Further analysis

Table of photoelectric effect work functions
Index

Millikan reference

Photoelectric effect
 
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Early Photoelectric Effect Data

Planck hypothesis

Index

Millikan reference

Photoelectric effect
 
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The Planck Hypothesis

In order to explain the frequency distribution of radiation from a hot cavity (blackbody radiation) Planck proposed the ad hoc assumption that the radiant energy could exist only in discrete quanta which were proportional to the frequency. This would imply that higher modes would be less populated and avoid the ultraviolet catastrophe of the Rayleigh-Jeans Law.

The quantum idea was soon seized to explain the photoelectric effect, became part of the Bohr theory of discrete atomic spectra, and quickly became part of the foundation of modern quantum theory.

Calculation

Interaction of radiation with matterElectromagnetic spectrumBasic quantum processes
Index

Photoelectric effect
 
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Photon Energies for EM Spectrum


x 10^ eV
eV =MeV =GeV

Wavelength


x 10^m

= m
= nm
= microns

Frequency


x 10^Hz

= kHz = MHz
= GHz
= 1/cm (wavenumber)

Planck hypothesis

Interaction of radiation with matter

Energies in electron volts

Index
 
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