1. The problem statement, all variables and given/known data Electrons with kinetic energy E are incident normally from vacuum on a metal surface. The work function of the metal is F. Calculate the fraction of electrons reflected from the surface. Neglect any temperature effects. 2. Relevant equations 3. The attempt at a solution Since work function is defined as the minimal energy required to extract one electron from the metal, all the electrons with energy larger than F will be reflected. From statistical mechanics, the so-called "electrons with kinetic energy E" are actually electrons with an energy distribution. My feeling is the this E is the average energy from this distribution. And the fraction of electrons reflected is the fraction of electrons with energy larger than F in this distribution. But I am wondering how I can get the distribution. Should I use Boltzman velocity distribution and derive the energy distribution? Or should it be a Gaussian distribution peaked at E? It never indicates the temperature in the problem, but I feel temperature should matter here. Any help is appreciated.