Duane-Hunt law (${\lambda }_{\min }=hc/(eV)$)

For an electron accelerated through a electric potential difference $V$ and stopped at a massive target, the largest single photon energy is approximately $eV$. Conservation of energy and $E_{\gamma }=hc/\lambda$ give the short-wavelength cutoff ${\lambda }_{\min }=hc/(eV)$. Target recoil is neglected in this limiting relation.