Electromagnets

Solenoids

A solenoid 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.A solenoid, shown here in cross section, has a stronger electromagnetic field than a single straight wire

Just as with the bar magnet, the strongest part of the electromagnet can be felt at the two ends.

Electromagnets

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

The strength of the electromagnet can be increased by passing more electric current through the coils and/or wrapping more coils around the iron core.

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.

Electromagnets have some advantages over permanent magnets. For example:

  • they can be turned on and off
  • the strength of the magnetic field can be varied

These properties make electromagnets useful for picking up scrap iron and steel in scrapyards.

An industrial magnet used to pick up scrap magnetic metal.