Electromagnets and solenoids

In a nutshell

Electromagnets are temporary magnets which can be switched on and off. The strength of an electromagnet can be changed by changing the number of turns of wire, the current flowing through the wire and by using a soft iron core.

Electromagnetic induction

When an electrical current flows through a wire, it creates a magnetic field around the wire. The magnetic field lines around a current carrying wire are circular and most concentrated nearest to the wire.

This means that the magnetic field is strongest next to the wire and weakens the further away the distance from the wire.

The diagram shows a current flowing through a wire. The current is travelling from the bottom of the image to the top. The magnetic field created by the wire is shown by the circular rings around the wire.

Closer to the wire, the field lines are closer together, showing that the magnetic field is stronger. The direction of the magnetic field is in the anti-clockwise direction.

If the current was reversed, the direction of the magnetic field would also be reversed.

Solenoids

A current travelling through a wire will only create a fairly weak magnetic field, which will be unlikely to interact with anything. When electrical appliances are turned on, magnetic materials don't all of a sudden start sticking to the wires.

If many wires were used, or the same wire but coiled up into a coil, then the magnetic field would strengthen. A wire which is made into a coil with lots of turns is called a solenoid. The magnetic field of each individual wire gets reinforced and made stronger.

Science; Magnetism; KS3 Year 7; Electromagnets and solenoids

The diagram shows the magnetic field around a solenoid. The magnetic field resembles something similar to a bar magnet.

The more coils a solenoid has, the stronger the magnetic field. When the current is switched off, the magnetic field disappears. This is now an electromagnet.

The main difference between a magnet and an electromagnet is that an electromagnet can be turned on and off using a switch whereas a magnet is more permanent.

Curiosity: Electromagnets are useful for picking up and dropping pieces of metal, like in scrap yards.

Making electromagnets stronger

The strength of an electromagnet can be increased or decreased as needed.

Adding more turns will produce a stronger magnetic field.
Using more current will produce a stronger magnetic field.
Adding a soft iron core will also increase the strength of an electromagnet.