A silicon sample is doped with phosphorus at 1.23 parts per million. Phosphorus acts as an electron donor, providing one free electron per atom. The density of silicon is 2.33 g/cubed cm and its atomic mass is 28.09 g/mol. Calculate the number of free electrons per unit volume of the doped silicon.
Compare the above result with the no. of conduction electrons per unit volume of copper wire, assuming that each copper atom produces one free conduction electron. The density of copper is 8.96 g/cm^3 and it's atomic mass is 63.54 g/mol.