Most people know what electricity
is. It comes out of the wall sockets in our homes and makes the lights
go on. It can hurt you if you touch it. Why is that? Why do you get a
shock when you touch a doorknob? Lightning looks like electricity. Why
Everything in the world is made up of tiny particles called atoms. They are so small that they cannot be seen even with a microscope. Atoms are made of two kinds of electric charge. In the middle of the atoms are the positive charges and flying around the outside are the negative charges.
Most of the time, there are just as many positive charges as negative
charges. Each positive charge has a negative partner. Sometimes,
however, there are too many of one kind of charge. These extra charges
go looking for a companion. These negative charges are called electrons
and are not held very tightly in the atom so it is easy for them to
move around. The moving electrons make up what we call electricity.
There are two kinds of electricity: static and current.
You are probably familiar with static electricity;
it is what makes your hair stand up when you rub a balloon against it
or gives you a shock from your doorknob. In static electricity,
electrons are moved around mechanically
(i.e. by someone rubbing two things together). When you drag your feet
across the carpet, extra charge is scraped off the rug and collects on
your body. When you touch a doorknob, all the charge wants to leave you
and go to the doorknob. You see a spark and get a shock as the
electrons leave you.
Lightning is the result of static electricity. In a thunderstorm, negatively charged particles can build up in a cloud. Electrons repel
each other; they really don’t like each other and want to get as far
away from each other as possible. The farthest they can get away from
each other is if they go into the ground because it’s the biggest thing
around. As the electrons jump to the group, we see lightning. It’s just
like a big spark. Benjamin Franklin found out that lightning can be
very dangerous. Lightning has more than 20 million Volts!
In current electricity, electricity has to flow in a closed loop called a circuit.
If the loop is broken anywhere, the electricity can’t get through. This
is like blood in the body. Blood gets pumped through your arteries by
the heart and eventually comes back to the heart through your veins. In
a circuit, electric charges are the blood and the wires are the
arteries and veins. Electric charges have a certain amount of energy.
The measure of this energy is called voltage (Volts).
A flashlight battery has about 1 ½ Volts and your wall socket
has about 120 Volts. The electrons moving through a circuit are called
a current. You can get an electric shock when a big current – lots of electrons – flows through your body.
The electrons in a circuit have to be pushed by something, like a battery.
If you look at one end of a battery, there is a + sign, this where the
extra positive charges are. At the other end, where there’s a – sign,
there are extra negative charges (electrons). When we turn on a
flashlight the electrons race out of the battery through the wires to
get to where the positive charges are. On their way, they run through
the wire inside the light bulb. The thin wire inside the bulb gets very
hot and makes light.
Wonders of Physics
University of Wisconsin
1150 University Ave
Madison, WI 53706