The electrochemical cell (battery) was the first continuous source of electricity to become available to scientists. To explore the mechanism by which a generator can transform mechanical energy into electrical energy, visit the interactive learning guide and explore the “Generator” app.
The electric motor
A battery supplies direct current (DC) by converting chemical energy into electrical potential energy.
The simplest and most convenient form of generator is a simple coil of wire being rotated in a magnetic field. Whenever there is a relative motion between a conductor and a magnetic field, a voltage is INDUCED (created) in the conductor. This is referred to as "Electromagnetic induction". This principle was discovered by Michael Faraday around 1830.
The direction of the electric current depends on the direction of the relative motion between the conductor and magnetic field. In the normal form of generator (as shown above) the voltage changes direction, going first in one direction and then in the other as ends of the coil of wire move up and then down through the magnetic field. This is termed an AC voltage (alternating) and produces an alternating current when operating a circuit. As you can see, the charges first go one direction, and then reverse and travel in the opposite direction.
Did you know? Most modern generators produce AC. In Australia, the AC has a frequency of 50 Hz, meaning that the current flows back and forth in the wire 50 times per second.
A battery (simple cell) supplies DC (direct current). This means that the current flows in the same direction, usually considered to be from positive to negative. In science we deal with conventional current, which was historically believed to be the flow of positive charge, i.e. it was thought that current flowed from the positive (+) terminal around the circuit to the negative (-) terminal. Today we know that it is the tiny negatively charged electrons that actually flow through wires as an electric current. The electrons flow from the negative terminal around to the positive terminal, i.e. an anti-conventional current.
In an AC circuit, the situation is quite different. When an AC power source is switched on, an electromagnetic effect travels through the conductors in the circuit close to the speed of light. This causes the electrons in the wire to start moving backwards and forwards in the wire, without actually flowing along the wire like a DC current.
Find out more about AC and DC.