Earth’s magnetism and the magnetic field of current

In 1820 the Danish physicist Oersted found that a magnetic needle next to a wire carrying current deflects: a magnetic field forms around a current. The field lines of a straight current-carrying conductor are concentric circles around the wire. Their direction is found with the gimlet rule: if the forward motion of a gimlet is in the direction of the current, the rotation of its handle shows the direction of the field lines. A wire wound in a spiral is a solenoid; its field resembles that of a bar magnet. The right-hand rule gives the north pole of a solenoid: if the four fingers point along the current, the thumb points toward the field lines (the north pole). The field grows stronger if the current or the number of turns is increased. Do the experiment only with the teacher and a low-voltage source; never connect to the mains, and switch the current on only briefly because the wire heats quickly.