The Photoelectric Effect

Test yourself

Photoelectric Effect

When light is shone on to a metal plate, electrons can be emitted. The conditions that determine whether electrons are emitted or not tell us a lot about the nature of light itself.

Illustrative background for Threshold frequencyIllustrative background for Threshold frequency ?? "content

Threshold frequency

  • Electrons are only emitted from a metal when the light hitting it is above a certain frequency.
  • Below this frequency, no electrons are emitted.
  • This frequency is called the threshold frequency.
  • Threshold frequency is different for different types of metal but is usually in the UV range.
Illustrative background for Kinetic energy variationIllustrative background for Kinetic energy variation ?? "content

Kinetic energy variation

  • The maximum kinetic energy of an emitted electron is dependent on the frequency of radiation but not its intensity (energy transferred per second).
Illustrative background for Above the threshold frequencyIllustrative background for Above the threshold frequency ?? "content

Above the threshold frequency

  • When the light (EM radiation) is above the threshold frequency of the metal, the number of electrons emitted is proportional to the intensity of the light.

Failure of Wave Theory

Wave theory wasn't able to account for the photoelectric effect.

Illustrative background for Threshold frequencyIllustrative background for Threshold frequency ?? "content

Threshold frequency

  • According to the wave theory of light, energy should be spread out evenly across the surface of the metal.
  • The energy absorbed by each electron would gradually increase so that after a while the electrons would have enough energy to be emitted.
Illustrative background for Intensity independenceIllustrative background for Intensity independence ?? "content

Intensity independence

  • According to the wave theory of light, the intensity should determine the energy transferred to the electrons each second.
  • So we would expect that the maximum kinetic energy of emitted electrons would increase with intensity (not frequency).

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

Go student ad image

Unlock your full potential with GoStudent tutoring

  • Affordable 1:1 tutoring from the comfort of your home

  • Tutors are matched to your specific learning needs

  • 30+ school subjects covered

Book a free trial lesson