The equation that relates resistivity , Electric field and current density (j) is $E = J \times \rho$
Since resistivity is a scalar quantity the direction of J must be in the direction of Electric field. I'm confused as to which electric field it is - inside the conductor or outside the conductor. My tutor said it was the direction of external electric field but my textbook says ;
Current per unit area (taken normal to the current, is called current denisty . Further if E is the magnitude of uniform electric field in conductor whose length is l, then the potential difference V across it's ends is E x l.
This contradicts what my teacher said , moreover, I can't understand how there could be a non zero uniform electric field inside a conductor. I heard him say that when in a DC source the frequency is zero so there's no entering of charge into the conductor (skin depth).