The Photoelectric Effect
Describe an interaction between photons and matter using the photoelectric effect.
- The photoelectric effect is the emission of electrons when electromagnetic radiation is incident upon a photoactive material.
- The emission of electrons via the photoelectric effect requires a minimum frequency of incident light, called the threshold frequency.
- Light that is incident on a material and is at the threshold frequency or higher will induce electron emission, regardless of the number of photons that strike the material.
- The energy of the emitted electrons is not dependent on the number of photons that are incident upon the material, which provides evidence that light is a collection of discrete, quantized energy packets called photons.
- The maximum kinetic energy of an emitted electron is related to the frequency of the incident light and the work function of the material, φ.
- The work function of a material is the minimum energy required to emit an electron from atoms in the material.
- The maximum kinetic energy of an emitted electron is given by the equation:
- In a typical experimental setup to demonstrate the photoelectric effect and determine the work function of a metal, two metal plates are placed in a vacuum chamber and connected to a variable source of potential difference. One of the plates is illuminated by monochromatic light that causes electrons to be ejected and the potential difference between the plates is adjusted until no current is measured in the circuit.
Where applicable, work functions for materials will be provided on the exam; students are not expected to know values of work functions or variables of a material that influence the magnitude of its work function.