ELECTRICITY
If you’ve ever sat watching a thunderstorm, with mighty lightning bolts darting down from the sky, you’ll have some idea of the power of electricity. A bolt of lightning is a sudden, massive surge of electricity between the sky and the ground beneath. The energy in a single lightning bolt is enough to light 100 powerful lamps for a whole day or to make a couple of hundred thousand slices of toast!
Electricity is the most versatile energy source that we have; it is also one of the newest: homes and businesses have been using it for not much more than a hundred years. Electricity has played a vital part of our past. But it could play a different role in our future, with many more buildings generating their own renewable electric power using solar cells and wind turbines. Let’s take a closer look at electricity and find out how it works!
What is electricity?
Electricity is a type of energy that can build up in one place or flow from one place to another. When electricity gathers in one place it is known as static electricity (the word static means something that does not move); electricity that moves from one place to another is called current electricity.
Static electricity
Static electricity often happens when you rub things together. If you rub a balloon against your jumper 20 or 30 times, you’ll find the balloon sticks to you. This happens because rubbing the balloon gives it an electric charge (a small amount of electricity). The charge makes it stick to your jumper like a magnet, because your jumper gains an opposite electric charge. So your jumper and the balloon attract one another like the opposite ends of two magnets.
Have you ever walked across a nylon rug or carpet and felt a slight tingling sensation? Then touched something metal, like a door knob or a faucet, and felt a sharp pain in your hand? That is an example of an electric shock. When you walk across the rug, your feet are rubbing against it. Your body gradually builds up an electric charge, which is the tingling you can sense. When you touch metal, the charge runs instantly to Earth—and that’s the shock you feel.
Lightning is also caused by static electricity. As rain clouds moved through the sky, they rub against the air around them. This makes them build up a huge electric charge. Eventually, when the charge is big enough, it leaps to Earth as a bolt of lightning. You can often feel the tingling in the air when a storm is brewing nearby. This is the electricity in the air around you. Read more about this in our article on capacitors.
Two kinds of static electricity
Electricity is caused by electrons, the tiny particles that "orbit" around the edges of atoms, from which everything is made. Each electron has a small negative charge. An atom normally has an equal number of electrons and protons (positively charged particles in its nucleus or centre), so atoms have no overall electrical charge. A piece of rubber is made from large collections of atoms called molecules. Since the atoms have no electrical charge, the molecules have no charge either – and nor does the rubber.
Suppose you rub a balloon on your jumper over and over again. As you move the balloon back and forward, you give it energy. The energy from your hand makes the balloon move. As it rubs against the wool in your jumper, some of the electrons in the rubber molecules are knocked free and gather on your body. This leaves the balloon with slightly too few electrons. Since electrons are negatively charged, having too few electrons makes the balloon slightly positively charged. Your jumper meanwhile gains these extra electrons and becomes negatively charged. Your jumper is negatively charged, and the balloon is positively charged. Opposite charges attract, so your jumper sticks to the balloon.
Photo: A classic demonstration of static electricity you may have seen in your school. When this girl touches the metal ball of a Van der Graaf static electricity generator, she receives a huge static electric charge and her hair literally stands on end! Each strand of hair gets the same static charge and like charges repel, so her hairs push away from one another.
Current electricity
When electrons move, they carry electrical energy from one place to another. This is called current electricity or an electric current. A lightning bolt is one example of an electric current, although it does not last very long. Electric currents are also involved in powering all the electrical appliances that you use, from washing machines to flashlights and from telephones to MP3 players. These electric currents last much longer.
Have you heard of the terms potential energy and kinetic energy? Potential energy means energy that is stored somehow for use in the future. A car at the top of a hill has potential energy, because it has the potential (or ability) to roll down the hill in future. When it’s rolling down the hill, its potential energy is gradually converted into kinetic energy (the energy something has because it’s moving).
Static electricity and current electricity are like potential energy and kinetic energy. When electricity gathers in one place, it has the potential to do something in the future. Electricity stored in a battery is an example of electrical potential energy. You can use the energy in the battery to power a flashlight, for example. When you switch on a flashlight, the battery inside begins to supply electrical energy to the lamp, making it give off light. All the time the light is switched on, energy is flowing from the battery to the lamp. Over time, the energy stored in the battery is gradually turned into light (and heat) in the lamp. This is why the battery runs flat.
Picture: A battery like this stores electrical potential energy in a chemical form. When the battery is flat, it means you’ve used up all the stored energy inside by converting it into other forms.
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