1. The problem statement, all variables and given/known data http://postimg.org/image/hf6zpmykr/ 2. Relevant equations intrinsic carrier density = ni = 10^10/cm^3 (for Si at 300K) 3. The attempt at a solution Its a really elementary problem but I can't figure out the difference between some quantities. For example, free electrons and holes would be in same quantity since the bar isn't dopped? Valence electrons and free electrons are the same thing ? And I can't see a way to calculate the numbers of atoms.