How Magnets Create Forces at a Distance

A bar magnet has a north-seeking pole and a south-seeking pole. Opposite poles attract, while matching poles repel. The force becomes weaker with distance, although the exact pattern depends on the magnets' shapes and strengths.

If a bar magnet is cut in half, each piece forms its own north and south poles. Ordinary magnets do not separate into one isolated north pole and one isolated south pole. The magnetic behaviour comes from organised effects throughout the material.

Iron, nickel and cobalt are strongly magnetic because groups of atoms can form regions called domains. In an unmagnetised piece, many domains point in different directions. When enough align, their effects reinforce one another and the object becomes magnetised.

Magnetic field lines are a model used to show field direction and relative strength. Outside a bar magnet, the conventional direction runs from the north pole towards the south pole. Closely spaced lines represent a stronger field.

Field lines are not physical threads filling space. They help you predict the direction a small compass would point at different locations. A compass needle is itself a tiny magnet, so it turns until it aligns with the local field.

When two magnetic fields overlap, their combined pattern explains attraction or repulsion. Unlike poles produce connecting field lines and pull together. Like poles create a region where the fields oppose one another, and the magnets push apart. The model gives the invisible interaction some visual manners.

Moving electric charges create magnetic fields. A current in a straight wire produces a circular field around the wire. Coiling the wire concentrates the field, creating an electromagnet with north and south poles.

Placing an iron core inside the coil can make the field much stronger because domains in the iron align. The electromagnet can be controlled by changing the current, the number of coil turns or the core material. Switching off the current removes most of the magnetic effect.

Electromagnets appear in relays, speakers, motors, lifting cranes and many other devices. Remember the core relationships:

• •Opposite poles attract.
• •Matching poles repel.
• •Closer field lines show stronger fields.
• •Electric current creates a magnetic field.
• •A coil and iron core strengthen an electromagnet.

Magnets exert forces through magnetic fields, with opposite poles attracting and matching poles repelling. Magnetic domains explain how some materials become magnets, while electric currents create controllable magnetic fields. Use field direction and strength to describe the interaction, and action at a distance stops feeling quite so mysterious.