Current electricity
Static electricity means charges that stay still; they don't
travel along wires or through the air. Current electricity is charges that are
continuously on the move and it is this kind of electricity which makes things
like light bulbs work. Thomas
Edison invented light bulbs at the age of 32. Power stations circulate electric current along the mains
wires to the places that need current electricity.
Like heat, electricity travels better through some materials
than others. Good conductors of electricity have many more "free"
electrons than insulators. Under normal conditions these electrons drift to and
fro from atom to atom to atom in a random way. Metals have lots of free
electrons, which is why they are good conductors.
If you look at a piece of electrical flex you will find one, two or more copper wires (good conductors) wrapped in rubber (an insulator) in order to insulate the wires and make them safe.
Whenever there are more electrons at one end than at the other end of a conductor, free electrons in the conductor are forced to move one way, as an electric current, towards the end with fewer electrons. The difference in electrons between one end and the other is called the potential difference and is measured in volts. A battery can set up a potential difference. Current is a measure of the number of electrons drifting along the wire, and is measured in amperes (or amps).
How a battery works
Inside a battery is a special chemical paste called the electrolyte that can conduct electricity. It is made of billions of positive and negative particles. The case of the battery is made of zinc and a carbon rod lies in the electrolyte. The zinc and carbon are both electrodes. A chemical reaction in the electrolyte sends positive particles to one electrode (the less reactive one) and negative particles to the other. When the electrodes are connected by touching metal parts of a torch, electric current flows. When the electrolyte is used up, the current cannot flow any more and the battery is "dead".
Stick 2 pieces of metal that are different into a lemon, making sure they are not touching each other. Wrap some copper wire around the ends of the metals, and connect the other ends of the wire to 1.5 volt torch bulb which is in a lamp holder. The lamp may light up. This is because the metals are acting as electrodes, and the lemon as the electrolyte. Why won't my lemon battery work?
Two sorts of electric current
The electric current a battery makes is called direct current (DC). It only flows in one direction. But the electric current that comes from power stations travels as "alternating current" (AC) which changes direction a hundred times a second. Alternating current can be transformed (using a "transformer") into higher voltages before it is sent over long distances. At high voltages less energy is lost as heat on the way.
While Van de Graaf generates static electricity, dynamo generates current electricity.
