Solenoids and Electromagnets

A solenoid is a coil of wire wound into a cylindrical shape. When a current flows through a solenoid it produces a magnetic field pattern similar to that of a bar magnet. This lesson covers solenoids, electromagnets and how to control their strength. It maps to AQA GCSE Combined Science Trilogy (8464) specification section 6.7.2 — The magnetic effect of a current.

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What Is a Solenoid?

A solenoid is a long coil of wire, usually wound into a tight helix (cylinder shape). When current flows through it, the magnetic fields from each loop of wire combine to produce a strong, uniform magnetic field inside the solenoid.

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Magnetic Field Pattern of a Solenoid

The magnetic field of a solenoid has two key features:

Inside the Solenoid

• The field is strong and approximately uniform (parallel, equally spaced field lines).
• The field lines run along the axis of the solenoid from one end to the other.

Outside the Solenoid

• The field pattern is identical to that of a bar magnet.
• Field lines emerge from the north pole end and curve around to enter the south pole end.