Electricity: A Brief Refresher Course
You will
have noticed that all computers run on electricity. So, it’s safe to say that
to understand how computers work you need some background knowledge about
electricity. You may already know some of this stuff, but (just in case) here’s
a brief refresher crash course. It doesn’t cover everything there is about electricity,
but it’s enough for this book. (I know there will be some scientists angry with
my descriptions, but I’m not making this book for other scientists. I’m doing
this for people who may not know what a “proton” is.)
What is Electricity?
Everything is made of atoms. Atoms are made of a nucleus (made
up of a collection of neutrons and protons) and electrons orbiting that
nucleus. Protons have a positive charge and electrons have a negative charge
(neutrons have no charge at all). Usually, the number of protons and electrons
in an atom are equal, meaning that atoms are normally balanced in charge. But
in some circumstances an atom can gain or lose electrons, resulting in an
imbalance in charge.
For example, when you rub a rubber balloon against hair the
balloon becomes a “magnet” for hair. This is because, as you rubbed the balloon,
atoms in the rubber were gaining extra electrons from the hair. This transfer
of electrons results in an imbalance in charge. The hair (with less electrons)
is now positively-charged and the balloon (with more electrons) is now
negatively-charged. Those positively-charged atoms in the hair naturally want
their stolen electrons back from the balloon, so the hair is drawn towards the
balloon. This is because positive and negative charges attract to each other
(like magnets). Eventually the hair gets their electrons back and everything
returns to normal for the atoms. Electricity is that movement of electrons.
The electricity that results from balloon-rubbing is known as “static electricity” – as each electron involved only jumps to just one positively-charged atom – and then stays there.
Electric Current
But what if you got a piece of material (say a length of
copper wire) and in that material, you were able to make an electron jump off
one atom to another that had an electron leave to jump to the next atom that
also had an electron leave to jump to the next atom and so on? Imagine electrons
jumping continuously along a row of atoms, like a pebble on water.
And imagine that this happened in a loop. What you got is a
continuous flow of electrons – an electric current.
Some materials (like
copper and water) “conduct” electricity because their atoms have “free” electrons
that can be easily spared to make current. Insulating materials (like glass and
PVC plastic) don’t have “free” electrons. Their electrons are trapped within
their atoms.
Making Current
To make a current flow in a loop of conducting material you’ll need something that’ll draw electrons away from atoms in one end of the loop. They are a number of ways to do this, but the most common way is by chemical reaction, mostly in the form of batteries. In batteries an acidic substance draws electrons off from the metal that makes the “positive terminal,” starting the chain reaction of jumping electrons along the loop. Meanwhile, the “negative terminal” (sometimes made of a different metal) receives electrons from the acidic substance, thus completing the loop.
Power sources, like batteries, act like water pumps – they provide the “electromotive force” that makes the electrons jump from one atom to another. This force is measurable and is measured in a unit you will have heard of – Volts.
Electric
We make use of electric current by making it flow around a circuit, where we can attach devices to.
In a “series” circuit everything is
connected to one single loop. In this circuit every device receives the same
amount of current, but the voltage is split between devices (exactly how much
it is split depends on how much pressure (voltage) each device needs to work). Because
of it been a single loop, if one component breaks in a series circuit, every
device powered by it will be without current.
In a “parallel” circuit the current is split into two or
more loops, which could each contain one or more device(s) (exactly how much water
(current) each loop gets depends on demand). Each loop receives the same pressure
(voltage), but if a loop has more than one device attached each device splits
the pressure (as in a series circuit).
Breaking the Loop
Current can only flow if there is a complete closed circuit
for the electron flow. If there is a break in a circuit the current will stop
flowing – unless the gap is small enough and the power source is cranking a
high amount of pressure (volts). This is how it’s possible for electricity to
arc between gaps. All electric sparks are created by high voltages – but there
current can be very low (low enough for you to survive, if you were stupid
enough to touch such sparks).
Resistance
If you are pumping something down a pipe, you’ll imagine that the substance would experience some friction with the walls of the pipe. This also happens to electric current in wires. The degree a material hinders the flow of current is known as electrical resistance. This resistance can be a nuisance (wasting energy as heat, which could potentially melt the wire) and can be exploited for useful purposes (like the heating element in a heat appliance).
Electromagnetism
Electricity and magnetism are interlinked things. Flowing electric current in a wire produces a very weak magnetic field.
But if you loop
wire around a metal bar that can stick to magnets (say an iron one) if current
flowed though that coil that bar becomes magnetic.
And the more times you loop wire around it the stronger the magnetism.
This electrically-generated magnetism can be used to move magnets (which is
exactly what happens in an electric motor).
But if you move a magnet inside a coil of wire
(continuously) you can “induce” electric current to move inside that coil
(which is how electric generators work).