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Science – Electric Generators
An electric current is a movement, or flow, of 'free' electrons, the tiny particles which usually circle the nucleus of an atom. The electrons jump from atom to atom when there is a difference of electrical voltage ('pressure') between the ends of a wire. The voltage is produced by ensuring that the atoms at one end of the wire are short of electrons (positively charged) while those at the other end of the wire have a surplus of electrons (negatively charged). By convention, a current is said to flow through a circuit from the positive terminal of a battery to the negative terminal. In fact, the moving electrons flow in the other direction.
Electricity
An electric current is a movement, or flow, of minute particles called electrons. Normally, electrons are attached to an atom and circle around its central nucleus in orbits just like artificial satellites orbiting the Earth. Each electron has the same charge or pack of electricity described as a negative charge. Usually the nucleus has exactly enough positive electrical charges to balance the negative charges on the electrons, so that the atom as a whole is neutral.
In some materials, however, a few of the electrons in each atom are only loosely held. These free electrons can jump from atom to atom, and it is a steady drift of free electrons that carries electricity through a wire.
Why should electrons move about between atoms? The basic law of electricity is that two similar charges (either both positive or both negative) repel each other and two opposite charges (one positive and the other negative) attract each other. Since electrons carry negative charges they are repelled by negatively charged atoms and attracted by positively charged atoms. As a result, the electrons are pushed around from atom to atom until they find one with a shortage of electrons. Alternatively, an electron may join a neutral atom if it pushes another electron out.
When some kind of driving force is applied to the wire, the wandering electrons are organized into a steady oneway drift. The driving force is simply a difference of electrical pressure (voltage) between the ends of the wire. It is provided by either a battery or generator. Electrical pressure starts the drift of electrons by pushing the loosely held electrons from the first atom in the line to the next and so on.
A current of electricity must have a completely unbroken path, or circuit. If we could follow a current as it flowed along a wire we should eventually arrive back at our starting point. Wires which carry an electric current are often made of copper. Copper, like most metals, is a good conductor of electricity. It has plenty of free electrons, so a current has little difficulty in traveling through copper. Materials such as rubber and plastics are good insulators (bad conductors). Their atoms do not have any loosely held electrons. When electric current flows through a conductor that offers resistance to its flow it heats the conductor. If the conductor is made of suitable resistance wire it will glow red and give off a good heat. This is the principle used in electric fires.
If conditions are suitable and the right type of resistance is chosen it will glow white hot and can be used to illuminate a room and light up the road ahead of an automobile.
