Building a DC Motor with a Battery

A simple direct-current (DC) motor is a classic physics demonstration that turns electrical energy into mechanical motion using a battery, a coil of wire, and a magnet. It illustrates the motor effect: when an electric current flows through a wire placed in a magnetic field, the wire experiences a force. By arranging a current-carrying coil near a magnet so that this force acts to turn it, the coil can be made to spin continuously, forming the heart of an electric motor.

In a basic build, a length of insulated wire is wound into a coil, and its ends are stripped and rested on two supports that also act as electrical contacts. A battery sends current through the supports and into the coil, and a permanent magnet is placed nearby. The interaction between the magnetic field of the magnet and the field produced by the current pushes one side of the coil up and the other down, starting it rotating. To keep the rotation going in one direction, the current must effectively reverse each half turn; in the simplest version this is achieved by stripping the insulation from only part of the wire ends, so the circuit is completed during part of each rotation.

The demonstration brings together several physics ideas: electric current, magnetic fields, and the force between them. It shows in a tangible way how the same principle scales up to the motors found in appliances, tools, and vehicles. Because the parts are inexpensive and the effect is immediate, it is a popular activity for introducing electromagnetism and the conversion between electrical and mechanical energy.

Frequently asked questions

What makes the coil in a simple DC motor spin?

Current flowing through the coil in the field of the magnet produces a force on the wire. This force pushes one side of the coil up and the other down, turning it.

Why does the motor need the current to switch each half turn?

Without reversing the effect of the current, the force would push the coil back and forth rather than keep it rotating. Switching it each half turn keeps the rotation going one way.

What physics principle does this experiment demonstrate?

It demonstrates the motor effect — that a current-carrying wire in a magnetic field experiences a force — and the conversion of electrical energy into mechanical motion.