When iron filings are placed near the permanent magnet, they line up with the magnetic field to reveal the magnetic field lines. The direction of magnetic field lines is defined as the direction in which the north end of a compass needle points. The pictorial representation of magnetic field lines helps visualize the strength, and direction of the magnetic field. The field lines are always directed from the north to south pole, along the tangent to the magnetic field at each point. Magnetic field lines always form closed loops. They are densely packed at the poles and are widely separated away from the poles. The magnetic field strength is proportional to the density of the field lines, implying the field is stronger near the poles and weaker away. If field lines intersect at a point, it implies two directions of the field, which is impossible. Hence, field lines cannot intersect. Magnetic field lines patterns produced by like and unlike magnetic poles, a straight current-carrying wire, and a horseshoe magnet are some common sources of magnetic fields.