Past exam of the physics A course of the University of Cambridge / 2012 / Paper 1 / Section A / 1

Subtract the two photoelectric effect equations $K_{\max }=hc/\lambda -\Phi$ to eliminate the work function:Here $e$ converts the energy difference from electronvolts to joules. The precision of the rounded stopping energies justifies about two significant figures, $6.7\times 10^{-34}\mathrm{J}\mathrm{s}$.