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Electromagnets and transformers - AQAWhat is an electromagnet?

Electromagnetism is due to the magnetic fields around electric currents. The fields can cause forces with other nearby magnets which can be used to make motors spin.

Part of Combined ScienceMagnetism and electromagnetism

What is an electromagnet?

When a current flows in a wire, it creates a circular around the wire. This magnetic field can the needle of a magnetic compass. The strength of the magnetic field is greater:

  • closer to the wire
  • if the current is increased
Wire runs vertically, current flowing bottom to top. Magnetic field rotates anticlockwise. Second wire runs vertically, current flowing top to bottom. Magnetic field rotates in a clockwise direction.

Solenoids

A consists of a wire coiled up into a spiral shape. When an electric current flows, the shape of the magnetic field is very similar to the field of a bar magnet. The field inside a solenoid is strong and uniform. The small magnetic fields caused by the current in each coil add together to make a stronger overall magnetic field.

Current flows towards you in the top five wires, away from you in bottom five. Magnetic fields flow anti-clockwise around top five wires, clockwise around bottom. North pole right. South pole left.
Figure caption,
A solenoid, shown here in cross section, has a stronger electromagnetic field than a single straight wire

Electromagnets

A solenoid with an iron core is called an . The iron core increases the solenoid鈥檚 magnetic field strength. A simple electromagnet is made by coiling wire around an iron nail.

A coil of insulated wire is wrapped around an iron nail. One end of the coil of wire is connected to a battery. The other is connected to a switch in the circuit.

Electromagnets are used in devices such as electric bells, and door locks that can be controlled remotely.