Equation relating the kinetic energy of an electron, emitted from a conductor illuminated by monochromatic photons, and the photon energy and work function of the surface from which the photoelectron is emitted. $½m_{\mathrm{e}}{\nu }_{\mathrm{m}\mathrm{a}\mathrm{x}}^2=h\nu -{\varphi }_0$, where $m_{\mathrm{e}}$ is the mass of an electron, ${\nu }_{\mathrm{m}\mathrm{a}\mathrm{x}}$ the maximum velocity of the emitted electron, $h$ the Planck constant, $\nu$ the frequency of the illuminating photons, and ${\varphi }_0$ the photoelectric work function of the surface.