Electric current can be induced into a wire by moving a magnet into or out of a loop of the wire. A current is produced by the relative motion between the magnet and the wire. So you can move the loop of wire while the magnet is stationary and also produce a current. If you move the magnet through more loops of wire, the induced current will be greater. This is because as you move the magnet and begin to induce a current, a magnetic field is formed around the wire. The more loops, the stronger the magnetic field (remember from the last tutorial that magnetic field lines get "bunched" inside a coil of wire, and the more coils the stronger the bunching effect?) The wire then repels the magnet. The more loops, the stronger the repelling force. So you have to do more work on the magnet to get it to move with respect to the wire. More work means more energy, which means a greater voltage and current.

The process of producing a current by relative motion between a magnetic field and a coil of wire is called electromagnetic induction. The phenomenon of electromagnetic induction was discovered by Michael Faraday in 1831. Faraday's law states that the induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within the loops. So the more loops and the greater the relative motion between coil and magnet, the greater the voltage. Induced current depends on these factors, but also on factors such as the resistance of the coil and the circuit the coil is connected to. For example, moving a magnet in and out of a doughnut, which is a loop, will produce a voltage but no current because of the doughnuts composition.

A generator operates on the principle of electromagnetic induction. The structure of a simple generator is very similar to that of a simple electric motor. A coil of wire is placed inside a magnet so that it can rotate. Two brushes are placed for the ends of the coil to rub against. The brushes are connected via some conductor to some device that needs electric power. The coil is rotated manually so that it moves relative to the magnet. An electric current is induced into the coil. When the ends of the coil rub against the brushes, the current is transmitted to the electrical device. As the coil rotates, it alternately produces positive and negative voltage because it changes direction with respect to the magnetic field. Therefore, a generator like this produces an alternating current.

Electric energy can travel across empty space. Consider two coils of wire, one connected to a battery or other voltage source and the other to an electrical device. The coil connected to the voltage source is called the primary. The coil attached to the electrical device is called the secondary. If we send a current through the primary, the secondary will register a brief current too. Here is why: as the current passes through the primary, the magnetic field of the primary changes. Since the secondary is close to the primary, the change in the primary's magnetic field is transmitted to the secondary. This means that a voltage, and therefore a current, is induced into the secondary. When the magnetic field of the primary stops changing, no more voltage is induced to the secondary. When the current in the primary shuts off, its magnetic field changes again. This induces a voltage in the secondary. The secondary responds to change in the primary's magnetic field. If the magnetic field of the primary is made to change constantly, by using an alternating current, a constant, alternating current will flow through the secondary. If a core of iron is placed through the coils of the primary and secondary, the energy transfer is more efficient. This more efficient machine is called a transformer.

If the primary and secondary of a transformer have an equal number of coils in them, the induced voltage in the secondary will be the same as the voltage in the primary. If the secondary has more coils than the primary, the induced voltage in the secondary will be greater than the voltage in the primary, or the voltage will be stepped up. If the secondary has less coils than the primary, the induced voltage in the secondary will be less than the voltage in the primary, or the voltage will be stepped down. The relationship between voltage, coils, and transformers is stated as primary voltage/# coils in the primary=secondary voltage/# coils in the secondary. The power in the primary always equals the power in the secondary. Electric power equals voltage multiplied by current. So primary_{voltage*current}=secondary_{voltage*current}. This means that if the voltage in the secondary is increased, it's current is reduced. A high current gives off a lot of energy and does not transport well. A low current is much more efficient. So power companies use transformers to step up the voltage in wires, then stepping down the current and losing less electrical energy in delivering the electricity.

Electromagnetic induction can be looked at in terms of electric fields. By Faraday's law, an electric field is created in any region of space in which a magnetic field is changing. An interesting effect, a counterpart to Faraday's law, was discovered by James Maxwell. Maxwell's law states that a magnetic field is created in any region of space in which an electric field is changing. Electricity and magnetism, two of the most important effects in today's world, are finally united with these two simple laws. Thank you Faraday and Maxwell.