Download What is electricity?

Conductors
Insulators
Circuit – the pathway taken by an electric current
Closed circuit
Open circuit
Series circuit – only one pathway for current
Parallel circuit – many pathways for current
Static electricity caused by rubbing certain things together
Electromagnet
How is electricity created by a moving magnetic field?
How is static electricity created and where does it occur in nature?
An electric current creates a magnetic field and a magnetic field creates electricity
Ben Franklin
Michael Faraday
Thomas Edison
Name ________________________________________________
Science SOL 4.3 – electricity
Benjamin Franklin was one of most innovative Americans of all time. Indeed, his
work and experiments resulted in several important discoveries and inventions
including electricity, bifocal glasses, a usable battery and many more.
Ben Franklin believed electricity could be harnessed from lightning. In 1752, he
devised an experiment to test his theory. Although details of the experiment
remain sketchy to this day, Franklin originally wanted to test his theory atop a
spire that was to be built on a Philadelphia church. As he thought about it in
detail, he realized that his theory could be better tested by using a mobile kite,
rather than a stationary spire. Franklin prepared the kite by tying a handkerchief
to two crossed sticks of proper length. Extending vertically about a foot from the
vertical stick was a wire. The apparatus was extended into the air by a length of
string. Along the string of the apparatus was a metal key that would apparently
conduct the electricity. Franklin hypothesized that the wire would draw 'electric
fire' from the thunder clouds which would then be conducted through the
apparatus and be contained in the key.
Franklin used his apparatus to test the idea in a Philadelphia field equipped with a
shed. Franklin kept his experiment a secret because he feared he would be
ridiculed. He only told his 21 year-old son who had assisted him in the kite's
construction. He stood in the field with the kite in the sky for some time. As
menacing clouds passed over head with no luck, Franklin became discouraged
and was about to go home. Suddenly, he observed some threads of the kite string
stand erect. Believing the cause to be an electrical current, Franklin extended his
knuckle to the key and was shocked (not seriously). Soon after, others witnessed
the experiment and it was proven (The French had actually conducted similar
experiences a month before).
Based on this landmark experiment, Franklin invented the first lightning rod. The
lightning rod was built to attract electricity to his house. The lightning rods were
attached to a system of bells that would ring throughout his house each time
electricity had been attracted. The sparks produced would illuminate the house.
Franklin's experiments helped the evolution of the common battery we use today.
Moving Electrons and
Charges
Electricity is related to charges, and both electrons and
protons carry a charge. The amount of the charge is the
same for each particle, but opposite in sign. Electrons
carry a negative charge while protons carry positive
charge. The objects around us contain billions and
billions of atoms, and each atom contains many protons
and electrons. The protons are located in the center of the
atom, concentrated in a small area called the nucleus. The
electrons are in motion outside of the nucleus in orbitals.
The protons are basically trapped inside the nucleus and
can't escape the nucleus. As a result, it is moving electrons
that are primarily responsible for 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 (tap), 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
move 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.
How static electricity works
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 center), 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 sweater 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.
Electric circuits
For an electric current to happen, there must be a circuit. A circuit is a closed path or loop
around which an electric current flows. A circuit is usually made by linking electrical
components together with pieces of wire cable. Thus, in a flashlight, there is a simple circuit with
a switch, a lamp, and a battery linked together by a few short pieces of copper wire. When you
turn the switch on, electricity flows around the circuit. If there is a break anywhere in the circuit,
electricity cannot flow. If one of the wires is broken, for example, the lamp will not light.
Similarly, if the switch is turned off, no electricity can flow. This is why a switch is sometimes
called a circuit breaker.
How electricity moves in a circuit
Materials such as copper metal that conduct electricity
(allow it to flow freely) are called conductors. Materials that
don't allow electricity to pass through them so readily, such
as rubber and plastic, are called insulators. What makes
copper a conductor and rubber an insulator?
A current of electricity is a steady flow of electrons. When
electrons move from one place to another, round a circuit,
they carry electrical energy from place to place like
marching ants carrying leaves. Instead of carrying leaves,
electrons carry a tiny amount of electric charge.
Electricity can travel through something when its structure
allows electrons to move through it easily. Metals like
copper have "free" electrons that are not bound tightly to
their parent atoms. These electrons flow freely throughout
the structure of copper and this is what enables an electric
current to flow. In rubber, the electrons are more tightly bound. There are no "free" electrons
and, as a result, electricity does not really flow through rubber at all. Conductors that let
electricity flow freely are said to have a high conductance and a low resistance; insulators that do
not allow electricity to flow are the opposite: they have a low conductance and a high resistance.
Electromagnetism
Electricity and magnetism are closely related. You might have seen giant steel electromagnets
working in a scrapyard. An electromagnet is a magnet that can be switched on and off with
electricity. When the current flows, it works like a magnet; when the current stops, it goes back
to being an ordinary, unmagnetized piece of steel. Scrapyard cranes pick up bits of metal junk by
switching the magnet on. To release the junk, they switch the magnet off again.
Electromagnets show that electricity can make magnetism, but how do they work? When
electricity flows through a wire, it creates an invisible pattern of magnetism all around it. If you
put a compass needle near an electric cable, and switch the electricity on or off, you can see the
needle move because of the magnetism the cable generates. The magnetism is caused by the
changing electricity when you switch the current on or off.
This is how an electric motor works: An electric
motor is a machine that turns electricity into mechanical
energy. In other words, electric power makes the motor
spin around—and the motor can drive machinery. In a
clothes washing machine, an electric motor spins the
drum; in an electric drill, an electric motor makes the
drill bit spin at high speed and bite into the material
you're drilling. An electric motor is a cylinder packed
with magnets around its edge. In the middle, there's a
core made of iron wire wrapped around many times.
When electricity flows into the iron core, it creates
magnetism. The magnetism created in the core pushes
against the magnetism in the outer cylinder and makes
the core of the motor spin around.
Michael Faraday (1791-1867)
British physicist and chemist, best known for
his discoveries of electromagnetic induction and of the laws of electrolysis. His biggest
breakthrough in electricity was his invention of the electric motor.
In the last two hundred years, people have learned to use electricity for their own purposes, to run
machines.
Conductor: When we want to move electricity around (like through a cord to your computer), we make
a long wire of copper atoms, because electrons move easily from one copper atom to another.
Insulator: When we want to keep electricity from moving (like out of the cord and onto your hand,
where it would give you a shock), we make a wrapper out of rubber or plastic, because electrons don't
move easily through those materials. We use electricity to heat our houses, light up dark rooms, cook
food, run washing machines, and listen to music. Some people use
electricity to run their car!
An open circuit doesn't, which means that it's not functional.
A closed circuit has a complete path for current to flow.
If this is your first exposure to circuits, you might think that when a circuit is open, it's like an open door
or gate that current can flow through. And when it's closed, it's like a shut door that current can't flow
through. Actually, it's just the opposite, so it might take awhile to get used to this concept.
Series Circuits
A series circuit allows electrons to follow only one path. All of the
electricity follows path #1. The loads in a series circuit must share the
available voltage. In other words, each load in a series circuit will use up
some portion of the voltage, leaving less for the next load in the circuit. This
means that the light, heat, or sound given off by the device will be reduced.
The only example of a series circuit I can give you is a flashlight.
Parallel Circuits
In parallel circuits, the electric current can follow more than one
path to return to the source, so it splits up among all the available
paths. In the diagram, some current follows path #1, while the
remainder splits off from #1 and follows path #2. Across all the
paths in a parallel circuit the voltage is the same, so each device will
produce its full output.
Static Electricity
You walk across the rug, reach for the doorknob and..........ZAP!!! You get a static shock.
Or, you come inside from the cold, pull off your hat and......BOING!!! Static hair - that static
electricity makes your hair stand straight out from your head. What is going on here? And
why is static more of a problem in the winter?
To understand static electricity, we have to learn a little bit about the nature of matter. Or
in other words, what is all the stuff around us made of?
EVERYTHING IS MADE OF ATOMS
Imagine a pure gold ring. Divide it in half and give one of the halves away. Keep
dividing and dividing and dividing. Soon you will have a piece so small you will not
be able to see it without a microscope. It may be very, very small, but it is still a
piece of gold. If you could keep dividing it into smaller and smaller pieces, you would
finally get to the smallest piece of gold possible. It is called an atom. If you divided it into
smaller pieces, it would no longer be gold.
Everything around us is made of atoms. Scientists so far have found only 115 different
kinds of atoms. Everything you see is made of different combinations of these atoms.
PARTS OF AN ATOM
So what are atoms made of? In the middle of each atom is a "nucleus." The nucleus
contains two kinds of tiny particles, called protons and neutrons. Orbiting around the
nucleus are even smaller particles called electrons. The 115 kinds of atoms are different
from each other because they have different numbers of protons, neutrons and electrons.
It is useful to think of a model of the atom as similar to the solar
system. The nucleus is in the center of the atom, like the sun in the
center of the solar system. The electrons orbit around the nucleus
like the planets around the sun. Just like in the solar system, the
nucleus is large compared to the electrons. The atom is mostly
empty space. And the electrons are very far away from the nucleus.
While this model is not completely accurate, we can use it to help us
understand static electricity.
(Note: A more accurate model would show the electrons moving in 3- dimensional volumes
with different shapes, called orbitals. This may be discussed in a future issue.)
ELECTRICAL CHARGES
Protons, neutrons and electrons are very different from each other. They have their own
properties, or characteristics. One of these properties is called an electrical charge. Protons
have what we call a "positive" (+) charge. Electrons have a "negative" (-) charge. Neutrons
have no charge, they are neutral. The charge of one proton is equal in strength to the
charge of one electron. When the number of protons in an atom equals the number of
electrons, the atom itself has no overall charge, it is neutral.
ELECTRONS CAN MOVE
The protons and neutrons in the nucleus are held together very tightly. Normally the
nucleus does not change. But some of the outer electrons are held very loosely. They can
move from one atom to another. An atom that loses electrons has more positive charges
(protons) than negative charges (electrons). It is positively charged. An atom that gains
electrons has more negative than positive particles. It has a negative charge. A charged
atom is called an "ion."
Some materials hold their electrons very tightly. Electrons do not move through them very
well. These things are called insulators. Plastic, cloth, glass and dry air are good insulators.
Other materials have some loosely held electrons, which move through them very easily.
These are called conductors. Most metals are good conductors.
How can we move electrons from one place to another? One very common way is to rub two
objects together. If they are made of different materials, and are both insulators, electrons
may be transferred (or moved) from one to the other. The more rubbing, the more
electrons move, and the larger the static charge that builds up. (Scientists believe that it is
not the rubbing or friction that causes electrons to move. It is simply the contact between
two different materials. Rubbing just increases the contact area between them.)
Static electricity is the imbalance of
positive and negative charges.
OPPOSITES ATTRACT
Now, positive and negative charges behave in interesting
ways. Did you ever hear the saying that opposites attract?
Well, it's true. Two things with opposite, or different charges
(a positive and a negative) will attract, or pull towards each
other. Things with the same charge (two positives or two
negatives) will repel, or push away from each other.
A charged object will also attract something that is neutral. Think about how you
can make a balloon stick to the wall. If you charge a balloon by rubbing it on your hair, it
picks up extra electrons and has a negative charge. Holding it near a neutral object will
make the charges in that object move. If it is a conductor, many electrons move easily to
the other side, as far from the balloon as possible. If it is an insulator, the electrons in
the atoms and molecules can only move very slightly to one side, away from the
balloon. In either case, there are more positive charges closer to the negative balloon.
Opposites attract. The balloon sticks. (At least until the electrons on the balloon slowly
leak off.) It works the same way for neutral and positively charged objects.
So what does all this have to do with static shocks? Or static electricity in hair? When
you take off your wool hat, it rubs against your hair. Electrons move from your hair to
the hat. A static charge builds up and now each of the hairs has the same positive charge.
Remember, things with the same charge repel each other. So the hairs try to get as far
from each other as possible. The farthest they can get is by standing up and away from the
others. And that is how static electricity causes a bad hair day!
As you walk across a carpet, electrons move from the rug to you. Now you have extra
electrons and a negative static charge. Touch a door knob and ZAP! The door knob is a
conductor. The electrons jump from you to the knob, and you feel the static shock.
We usually only notice static electricity in the winter when the air is very dry. During the
summer, the air is more humid. The water in the air helps electrons move off you more
quickly, so you can not build up as big a static charge.
Thomas Edison's greatest challenge was the development of a practical incandescent,
electric light. Contrary to popular belief, he didn't "invent" the light bulb, but rather he
improved upon a 50-year-old idea. In 1879, using lower current electricity, a small
carbonized filament, and an improved vacuum inside the globe, he was able to produce a
reliable, long-lasting source of light. The idea of electric lighting was not new, and a number
of people had worked on, and even developed forms of electric lighting. But up to that time,
nothing had been developed that was remotely practical for home use. Edison's eventual
achievement was inventing not just an incandescent electric light, but also an electric
lighting system that contained all the elements necessary to make the incandescent light
practical, safe, and economical. After one and a half years of work, success was achieved
when an incandescent lamp with a filament of carbonized sewing thread burned for thirteen
and a half hours.