- 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 the Planck 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 states that…
- electromagnetic radiation is composed of discrete entities called photons
- the energy of a photon is proportional to its frequency
- the work function of a material is the energy needed per photon to extract an electron from its surface
- photoelectric effect
Kmax = E − ϕ = h(f − f0)
- photon energy
E = hf = hc λ
- work function
ϕ = hf0 = hc λ0
- stopping potential
Kmax = eV0
- photoelectric effect