Magnetic fields and bar-magnet field lines

A magnetic field is a region in which a magnetic pole experiences a force. At any point in the field, the field direction is the direction of the force on a north pole placed at that point.

Magnetic field lines represent the pattern and direction of a magnetic field. Arrows on the lines show the field direction: a north pole placed at a point on a line would experience a force along the line, in the direction of the arrow.

Field lines around a bar magnet

Outside a bar magnet, field lines curve from the magnet’s north pole towards its south pole. A field-line diagram shows this curved pattern around both sides of the magnet, with arrows pointing from north to south.

Magnetic field strength and field-line spacing

Magnetic field lines are used to show how the strength of a magnetic field varies from place to place. Their spacing indicates the relative field strength:

• Where the lines are closer together, the field is stronger.
• Where the lines are farther apart, the field is weaker.

Around a bar magnet, the field lines are closest together near the poles. This shows that the field is strongest near the poles and weaker where the lines spread farther apart.