Electricity (an Introduction)
Created | Updated Sep 5, 2003
Not quite everything you never wanted to know about Electricity, but quite a lot of it
Electricity is the term relating to the motion of charge1.
Electrical energy is one of the most useful in the universe. It can travel great distances, and can be controlled. It is most useful, however, because you can convert it easily to other forms of energy: eg: heat (electric heaters), light (light bulbs) and motion (motors).
Electricity is generally the flowing of electrons through a conductor, such as a Wire.
The electrons themselves do not move fast, but the effect is felt through the whole wire almost instantly, like the effect of turining on the cold tap at home is almost instant, despite the speed of the water. The electrons typically move about 35cm per hour, or 0.0002 mph.
There is also Static Electriciy, not covered on this page.
Electricity can be Dangerous!
If you muck about with electricity, especially at high voltages, you will risk Electrocution and Death! Sometimes it is unavoidable, for example if you get stuck on electricity wires.
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Electric Personalities
William GilbertThe term 'electricity' was coined by English pysicist William Gilbert (1544 - 1603) based on the Greek word 'elektron' for amber. Gilbert re-discovered what the Greeks had already observed, namely that amber could attract small stuff like dust particles when rubbed with a piece of fur.2
The American Benjamin Franklin FRS* (1706 - 1790) experimented with electricity using a kite, a key and lightning, proving lightning was a form of electricity. He also deduced the fact that two items can be charged negatively and positively. He coined these, and most of the other words to do with electriciy, and also invented the lightning conductor.
Thomas Edison (1847 - 1931) made the light bulb economical, making electricity useful for the first time. He also helped define how electricity works.
Alessandro Volta (1745 - 1827) invented the Battery in 1800, though electricity was known about since the Greeks.
The german Prof. Georg Simon Ohm (1789 - 1854)
published his law on resistance in 1827
Some Sources of Electricity
Conductors and Insulators
Conductors allow electricity to flow through them easily. Insulators do not. Most conduators are made of metal. For more info look at Conductors and Insulators.
In addition there are Semiconductors, is something that conducts only a little bit. You don't need to think about this unless you have a PhD in Life, the Universe and Everything.
In general, electricity will only flow along conductors, like wires. Electricity flows between a difference in potential (or voltage) along these wires. A battery produces this difference in potential (also known as the Electromotive Force), so connecting wires to each side in a circle creates a complete circuit, and electricity will flow. Components use the potentail (voltage).
Birds (eg: pigeons4) perching on electricity wires do not get electricuted because there is no difference in potentail between their two feet, so electricity will not flow through them.
Current
Current is the rate flow of charged particles5 (usually electrons through a wire). Current is said to flow in the opposite direction to the charge6.
Current is measured in amperes (amps). You can use an ammeter to measure current.
Current is subdivided into two categories:
- Alternating Current which switches direction very fast
Direct Current which flows in one direction
Voltage
Voltage is the energy held by one coulomb of electrons.
Voltage created is known as the Electromotive Force (EMF) while the voltage used by a component in the circuit is called the Potential Difference (p.d.).
Voltages are measured in Volts. You can use a voltmeter to measure voltage. Common voltages are:
230 Volts AC for Mains
1.5 Volts DC for a small button battery (technically called a Cell)
9 Volts for a big, chunky battery
Why big power lines have a high voltage
Power loss is increased by having a large current and resistance. (Energy "loss" = Current2 x Resistance. The power lines have a very low current to reduce the energy loss, but decreasing the current means they must increase the voltage.
Changing voltage from one level to another
Transformers allow this. Not to be confused with robots in disguise, they typically look like big plugs. They step up or down voltage by converting electriciy to magnetism, then back to electriciy again. They need an AC supply to work.They are typically lots and lots of coils of wires around a metal core.
The ratio of the number of turns is the same as the ratio of the voltages7. V1/V2 = N1/N2
Resistance
Resistance is a measure of how difficult electricity finds it to travel through a component8. As a rule of thumb, electricity tries to take the least difficult path. It's measured in Ohms, and measured with the imaginatively named Ohmmeter.
Power
Power is the energy used per second, measured in watts. It is equel to the voltage times the current (P = I x V).
Magnetism
When a current flows through a wire, it creates a magnetic field, for use in things like Electromagnets. Like any magnetic field, this creates a force between it and any magnets. This force can be used in Motors.
Electricity can be made by cutting lines of magnetic flux, a phrase which actually means waving a wire near to a magnet (a current will flow through the wire while it moves).
The english Michael Faraday (1791-1867) was responsible for discovering this link between Electricity and Magnetism, published his laws of electrolysis in 1833. He had the unit of capacitance (the Farad, Fa) named after him and he also discovered Classical Field Theory
1There are very few definitions of charge, one being an "An Accumilation of Electricity" - Chamber's Maxi Paperback Dictionary2According to Hell3Batteries are a collection of cells. Cells are wads of metal covered in a thick goo of acidic chemicals4This is a plug for an entry on pigeons5You could use anything: electrons, positrons, ions, protons. In fact, anything with a charge6If you use positively charged particles, it goes in the same direction7For what is known as an ideal transformer, one with no power or energy lost8Resistivity is how difficult electricity flows through different materials, eg: Iron, Copper, etc. Resistance depends on this and the thickness and length of the item through which it wants to flow. You can use the formula Resistance = Resistivity x Length / Cross-sectional Area.
