The Photoelectric Effect and Wave Theory
The Threshold Freuquency
- Wave theory says that for a particular frequency of EM wave, the energy carried should be proportional to the intensity of the beam.
- The energy carried by the EM wave would also be spread evenly over the wavefront. This means that if an EM wave were shone on a metal, each free electron on the surface of the metal would gain a bit of energy from each incoming wavefront. Gradually, each electron would gain enough energy to leave the metal.
- If the EM wave had a lower frequency (i.e. was carrying less energy) it would take longer for the electrons to gain enough energy, but it would happen eventually. However, electrons are never emitted unless the wave is above a threshold frequency — so wave theory can't explain the threshold frequency.
Kinetic Energy of Photoelectrons
- The higer the intensity of the wave, the more energy it should transfer to each electron. The kinetic energy of the electrons should increase along with intensity.
- Wave theory can NOT explain the fact that kinetic energy depends only on frequency in the photoelectric effect.