Photoelectric Effect

Summary

Electromagnetic radiation can push electrons free from the surface of a solid.
- This process is called the photoelectric effect.
- A material that can exhibit the photoelectric effect is said to be photoemissive.
- Electrons ejected by the photoelectric effect are called photoelectrons.
The photoelectric effect will not occur when the frequency of the incident light is less than the threshold frequency.
- Different materials have different threshold frequencies.
- Most elements have threshold frequencies in the ultraviolet region of the electromagnetic spectrum.
The maximum kinetic energy of a stream of photoelectrons …
- is determined by measuring the stopping potential: the applied voltage needed keep the photoelectrons trapped in the photoemissive surface.
- increases linearly with the frequency of the incident light above the threshold frequency.
- is independent of the intensity of the incident light.
The rate at which photoelectrons are emitted from a photoemissive surface …
- is determined by measuring the electric current.
- is directly proportional to the intensity of the incident light when frequency is constant.
On a graph of maximum kinetic energy vs. frequency …
- all curves are linear with slope equal to Planck's Constant.
- the intercept on the energy-axis is the threshold frequency of the material.
Classical physics cannot explain why …
- no photoelectrons are emitted when the incident light has a frequency below the threshold,
- the maximum kinetic energy of the photoelectrons increases with the frequency of the incident light,
- the maximum kinetic energy of the photoelectrons is independent of the intensity of the incident light, and
- there is essentially no delay between absorption of the radiant energy and the emission of photoelectrons.
Modern physics … something, something …
- photon energy
- work function
- more?
Equations
- photoelectric effect
  K_max = E − ϕ = h(f − f₀)
- photon energy
  
  E = hf = hc
  
  λ
- work function
  
  ϕ = hf₀ = hc
  
  λ₀
- electron energy
  K_max = eV₀

The Physics Hypertextbook

No condition is permanent.

ϕ = hf₀ =	hc
	λ₀