Force on a Current-Carrying Conductor

The motor effect, step by step.

A wire carrying current inside a magnetic field feels a force at right angles to both the field and the current. Fleming's left-hand rule gives the direction: first finger for field, second finger for current, thumb for force.

In a simple DC motor a coil sits between magnet poles. Opposite sides of the coil feel opposite forces, so it turns. A split-ring commutator reverses the current every half turn so the rotation continues in one direction.

• Force is largest when the wire is at 90° to the field.
• No force acts when the wire is parallel to the field.
• Larger current or stronger field gives a stronger push.

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