1. The problem statement, all variables and given/known data Determine the number of K electrons ejected from a foil of lead with thickness 0.5 x 10^20 atoms/cm^2. It is bombarded by 10^4 photons that each have an energy of 88keV. 2. Relevant equations From a figure in the book, it shows that u/p (7.483 cm^2/g = .7483 m^2/kg). I think this is the mass attenuation coefficient. Z = 82. I think this is the atomic number and is the number of electrons per atom. The density of lead is 11360 kg/m^3 and the number of electrons per g is 2.38 x 10^23 electrons/g. 3. The attempt at a solution We need to find number of electrons. We know thickness, initial number of photons, their energy, and u/p which is the mass attenuation coefficient I think. I'm not really sure of an equation that can relate this information to the number of electrons ejected. I know the answer is 903 K electrons because that's what the book gives. Can anyone help?