Introduction

A potential difference is induced in a wire when it cuts through magnetic field lines. If the wire forms part of a complete circuit, then an induced current will flow.

Electricity is usually produced using a generator. Generators can be found in bicycle dynamos and all power stations.

The simplest way of generating a continuous supply of electricity is with an

alternating current

Alternating current (often abbreviated to a.c.) is when the flow of electric current changes direction periodically. The mains is a source of alternating current.alternating current (

a.c.

The common abbreviation for alternating current is a.c. This is when the flow of electric current changes direction periodically. The mains is a source of alternating current.a.c.)

generator

A generator is a device that creates electrical energy.generator. Rather than moving a single wire between two magnets, a generator has a coil of wire rotating in a

magnetic field

Around every magnet there is an invisible magnetic field.magnetic field. A model of such a

generator

A generator is a device that creates electrical energy.generator is shown in Fig.1.

Before you run the generator, think about which way you expect the current to flow through the wires. If the coil rotates clockwise, the red wire will periodically move upwards. Use Fleming's right-hand rule to predict which way the current will flow in the red wire when it moves upwards.



Rotate the coil by clicking on the buttons. The induced current is shown on the ammeter. The needle points to the right when the current is positive. The direction of the

conventional current

Conventional current flows from positive to negative around a circuit. However, electrons in the wire actually flow from negative to positive.conventional current flow is indicated by the arrows next to the wires and the symbols on the coil. A dot means the current is coming towards you (like the tip of an arrow), while a cross means the current is flowing away from you (like the end of an arrow).



Watch the pointer on the ammeter as the coil rotates. The current is not constant – it varies between flowing in one direction and the other.



The current flowing through the circuit is an alternating current (a.c.). This type of generator is often called an

alternator

An alternator is a type of generator that creates alternating current.alternator.

The magnitude of the current generated by the alternator depends on how fast the coil rotates. In Fig.2 below, the

speed

Speed is a measure of how fast something is moving. It is calculated by dividing the distance travelled by the time taken.speed of rotation of the coil is controlled by the slider.



Set the rotation speed to the maximum positive value. Observe the shape that the crosses on the graph make.



The experiment in Fig.3 below draws a smooth wave. Use it to see the exact shape of the a.c. current wave.



The electricity in your house varies in just the same way as the electricity produced by the alternator.

This is because the large generators in

power

Power is the rate of doing work, or the rate of energy transfer. The unit of power is the watt, W.power stations are very similar to the alternator. The main difference is that in the power station, the coils are fixed in place around the rotating magnet.

Summary


A device that creates electrical energy is called a generator.

When a coil of wire rotates in a magnetic field, an alternating current (a.c.) is produced. This is why this type of generator is called an alternator.

The amplitude of the current produced by an alternator depends on the speed of rotation of the coil.

The current produced by an alternator has the form of a wave.