Question

what do the magnetic field lines in a bar magnet depend on?

Answer 1

magnetic effect of electric current

Answer 2

Magnetic field lines are a vector quantity, i.e., it has both direction and magnitude. By convention they move from the north pole and meet at the South Pole. Inside the magnet they move from the South to the north pole. This the magnetic field lines are closed curves. The relative strength of the magnetic field depends on the degree of closeness of the field lines. No two magnetic field lines meet each other.