The photoelectric effect describes the emission of electrons when light shines on a material. The kinetic energy of these emitted electrons depends on the frequency of the incident light and the work function of the material. Specifically, $KE_{max} = hf - \phi$, where $KE_{max}$ is the maximum kinetic energy, $h$ is Planck's constant, $f$ is the frequency of light, and $\phi$ is the work function of the metal.