Photoelectric effect graph

If we plot a graph of the maximum kinetic energy of the emitted electrons against the frequency of the incident light (the frequency of the photons that hit the electrons), we get a graph that looks like this:

Key identities

• The x-intercept of the graph is the threshold frequency of the metal.
  • Remember that the threshold frequency is the minimum frequency of light that can cause an electron to be released.
• The y-intercept of the graph is the negative of the work function of the metal.
  • work function is the minimum energy required to release an electron from the metal.
• The gradient of the graph is Planck’s constant (h).
  • That’s because, if we rearrange the equation for the energy of a photon (E=h\times f) to find the kinetic energy of the emitted electron, we get:
  • h=\frac Ef
  • …and \frac Ef is the gradient of the graph!