CURRENT ELECTRICITY
We are reasonably familiar with some aspects of hooking up electrical circuits as most of us have connected wires, batteries and light bulbs sometime at school but maybe it didnít entirely gel as logical and sensible.
Words associated with electricity include
circuits, resistance, conductors, current, voltage, power, cells, batteries, ohms, voltmeters, ammeters, ……………….. .
These seem confusing and at times, interchangeable.
Let us go over real basics.
To make “something” (refrigerator, light, computer, radio controlled car, sewing machine……) turn on we need
an appropriate source of electricity,
metal wires insulated with plastic,
a switch
and the thing.
We connect them in a distinct sequence for the thing to work.
The source is a source of energy.
– In the case of a 1.5V AA cell, it has a limited life then is unusable so we throw it away.
– In the case of the 240V Hydro provided electricity, it is far closer to limitless as an energy source. (The energy can be traced back to Gravitational potential energy of water.) The limitations are – what you can afford to buy, or, how much Tasmanians are prepared to allow to be created.
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The energy is transferred to the globe or CD player where it changes to light or heat or motion or sound – all forms of energy. Because the connecting wires are extremely good conductors of electricity, very little energy is lost as heat in them. The switch merely allows or stops the transfer of energy.
But why is it necessary to have two wires? Surely the transfer can take place with only one wire? The answer lies in the method of transfer – the motion of electrons from high potential energy in the source to low potential energy in the source. One wire carries electrons to the globe or CD player from the source, the other returns them to the source whereupon they are boosted back up to continue their circulation.
In any material, especially conducting material, electrons on the outside of atoms are relatively free to migrate around the atomic crystal structure which, of course remains in place.
This flow of electrons around the wires through both the source and CD player is continuous while the switch is closed turning on the player. Because it makes a continuous loop, we call the arrangement a circuit.
The flow of electrons is called a current, an electric current. They flow from high to low energy in response to an electric field established in the wires and CD player- a region of influence on charges by other charges.
You may remember something about “like charges being repelled”. That is precisely what is happening in the circuit, negative electrons are being repelled from the “negative terminal” of the source and subsequently attracted to the positive terminal. The source uses energy from some other means to keep the electrons flowing WITHIN the source from positive to negative – chemical or mechanical energy. This completes the loop.
A crude but useful analogy can be made to a continuous water loop in a modern entertainment park. (Unfortunately Tasmania lacks one of these so far, so go to Sydney to try one.)
Think of the rafts as electrons, the moving ramp as the battery or mains, the gentle start and finish as the connecting wires, and the rapid as the CD player where the energy is lost.
The rafts move in a continuous circuit and are responding to the change in gravitation potential energy given them by the ramp. Most energy is lost in the rapid where the thrills are. The rafts, like the actual electrons, are merely responding to conditions around them, the energy change, the physical make up of the surrounding river bed, etc. Electrons respond similarly to things like the material they are moving through ( crystal structure, surrounding atom types, magnetic fields etc).
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Notice — provided some cantankerous old sod isn’t sinking or removing rafts, the number of rafts passing anyone watching, anywhere, is the same in say, an hour! — which means that in a real circuit, the number of electrons entering and leaving the battery in say, a second, is the same. — (think about it.) This is important.
