Chapter 9, Problem 9.34E

Work functions $\varphi$ are typically given in units of electron volts, or $\text{eV}$. $\text{1}\text{eV}$ equals $\text{1}\text{.602}\times {\text{10}}^{-19}\text{J}$. Determine the minimum wavelength of light necessary to overcome the work function of the following metals (“minimum” implies that the excess kinetic energy, $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\text{mv}}^{\text{2}}$, is zero): $\text{Li}$, $\text{2}\text{.90}\text{eV}$; $\text{Cs}$, $\text{2}\text{.14}\text{eV}$; $\text{Ge}$, $\text{5}\text{.00}\text{eV}$.