Magnetic Fields of a Solenoid

When an electric current flows through a wire it creates a magnetic field around the wire. In this lesson you will learn about the magnetic field patterns around a straight wire and a solenoid, and how to increase the strength of an electromagnet. This is part of AQA GCSE Physics specification 4.7.

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Magnetic Field Around a Straight Current-Carrying Wire

When a current flows through a straight wire, a magnetic field is produced around the wire. The field lines form concentric circles centred on the wire.

Key Features

• The field lines are circular, centred on the wire.
• The field is strongest close to the wire (the circles are closest together).
• The field gets weaker further from the wire (the circles spread out).
• The direction of the field depends on the direction of the current.

graph TD
    subgraph "Field Around a Straight Wire (view from above)"
        W["Wire (current flowing UP out of page)"] --> C1["Circular field line (anticlockwise)"]
        C1 --> C2["Larger circular field line"]
        C2 --> C3["Even larger circular field line"]
    end

The Right-Hand Grip Rule (for a wire)