lesson
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Every time an electric car accelerates, a drone lifts off, or a computer fan spins up, electrical energy is converted directly into mechanical motion. But how does a completely stationary magnet push a wire into spinning millions of times without stopping?
To understand that spin, we first need to look at what happens when a single wire carrying electric current enters a magnetic field.
The Motor Effect and Fleming's Left-Hand Rule
When an electric current flows through a wire placed inside an external magnetic field, the two magnetic fields interact and produce a mechanical push called the motor effect. In 1885, physicist John Ambrose Fleming developed a simple hand rule to predict the exact direction of this resulting push.
Fleming's Left-Hand Rule uses three perpendicular fingers: your Thumb points in the direction of the Force (motion), your First finger points along the external magnetic Field (North to South), and your seCond finger points along the conventional Current (positive to negative).
📊Interactive diagram
A single straight wire only gets pushed once in a single direction. How do we arrange wires so that this push turns into continuous rotation?
Key Parts of a Simple DC Motor
A simple direct current (DC) motor consists of a rectangular coil of wire (armature) mounted on an axle between two opposite magnetic poles. Electric current enters and leaves the spinning coil through a pair of stationary carbon brushes pressing against a rotating split-ring commutator.
📊Interactive diagram
The split-ring commutator is a conductive ring split into two halves that rotates along with the coil. The stationary carbon brushes maintain an electrical sliding contact with the ring halves so wires do not twist and snap as the coil spins.
Now let's trace the electricity through the loop to see why the entire frame starts spinning.