magnetic field

A magnetic field is the invisible region around a magnet or a current-carrying wire where magnetic forces can act.

• You cannot see a magnetic field directly, but you can detect it by its effects. For example, a compass needle turns because it responds to the magnetic field around it.
• For a straight wire carrying electric current, the magnetic field forms circular loops around the wire. The circles are closest together near the wire, where the field is strongest.
• The direction of the field depends on the direction of current. If the current is reversed, the magnetic field direction also reverses.
• Imagine the field as invisible “instructions” around the wire that tell a tiny compass needle which way to point.
• When the current stops, the wire’s magnetic field stops too. This makes it possible to switch magnetic effects on and off in devices such as electric bells, motors, and electromagnets.