A question on semiconductors. I need to determine the carrier concentration and type. I have worked out the type but its the conc. that is getting me. I have the conc., n, as: n = wBJ / eV w is the width of sample, B the mag. field, e is charge, and V the Hall voltage...these are all known EXCEPT J. Now the only other pieces of info I have are the sample dimensions and the battery voltage that supplies the current. I cant for the life of me see where I find J. I just cant get it! Any pointers in the right directions?