Resistance and Static Electricity
As we have learned, some kinds of atoms contain loosely
attached electrons. Electrons can be made to move easily from
one atom to another. When those electrons move among the atoms
of matter, a current of electricity is created.
Take a piece of wire. The electrons are passed from atom to
atom, creating an electrical current from one end to the other.
Electrons are very, very small. A single copper penny contains
more than 10,000,000,000,000,000,000,000 (1x1022)
electrons.
Electricity "flows" or moves through some things
better than others do. The measurement of how well something
conducts electricity is called its resistance.
Resistance in wire depends on how thick and how long it is,
and what it's made of. The thickness of wire is called its guage.
The smaller the guage, the bigger the wire. Some of the largest
thicknesses of regular wire is guage 1.
Different types of metal are used in making wire. You can
have copper wire, aluminum wire, even steel wire. Each of these
metals has a different resistance; how well the metal conducts
electricity. The lower the resistance of a wire, the better it
conducts electricity.
Copper is used in many wires because it has a lower
resistance than many other metals. The wires in your walls,
inside your lamps and elsewhere are usually copper.
A piece of metal can be made to act like a heater. When an
electrical current occurs, the resistance causes friction and
the friction causes heat. The higher the resistance, the hotter
it can get. So, a coiled wire high in resistance, like the wire
in a hair dryer, can be very hot.
Some things conduct electricity very poorly. These are
called insulators. Rubber is a good insulator, and that's why
rubber is used to cover wires in an electric cord. Glass is
another good insulator. If you look at the end of a power line,
you'll see that it is attached to some bumpy looking things.
These are glass insulators. They keep the metal of the wires
from touching the metal of the towers.
Static Electricity
Another type of electrical energy is static electricity.
Unlike current electricity that moves, static electricity stays
in one place.
Try this experiment...
Rub a balloon filled with air on a wool sweater or on your
hair. Then hold it up to a wall. The balloon will stay there by
itself.
Tie strings to the ends of two balloons. Now rub the two
balloons together, hold them by strings at the end and put them
next to each other. They'll move apart.
Rubbing the balloons gives them static electricity. When you
rub the balloon it picks up extra electrons from the sweater or
your hair and becomes slightly negatively charged.
The negative charges in the single balloon are attracted to
the positive charges in the wall.
The two balloons hanging by strings both have negative
charges. Negative charges always repel negative charges and
positive always repels positive charges. So, the two balloons'
negative charges "push" each other apart.
Static electricity can also give you a shock. If you walk
across a carpet, shuffling your feet and touching something made
of metal, a spark can jump between you and the metal object.
Shuffling your feet picks up additional electrons spread over
your body. When you touch a metal doorknob or something with a
positive charge the electricity jumps across the small gap from
your fingers just before you touch the metal knob. If you walk
across a carpet and touch a computer case, you can damage the
computer.
One other type of static electricity is very spectacular.
It's the lightning in a thunder and lightning storm. Clouds
become negatively charged as ice crystals inside the clouds rub
up against each other. Meanwhile, on the ground, the positive
charge increases. The clouds get so highly charged that the
electrons jump from the ground to the cloud, or from one cloud
to another cloud. This causes a huge spark of static electricity
in the sky that we call lightning.
You can find out more about lightning at Web Weather for
Kids - www.ucar.edu/40th/webweather/
But What Is Static Electricity?
You'll remember from Chapter
2 that the word "electricity" came from the Greek
words "elektor," for "beaming sun" and
"elektron," both words describing amber. Amber is
fossilized tree sap millions of years old and has hardened as
hard as a stone.
Around 600 BCE (Before the Common Era) Greeks noticed a
strange effect: When rubbing "elektron" against a
piece of fur, the amber would start attracting particles of
dust, feathers and straw. No one paid much attention to this
"strange effect" until about 1600 when Dr. William
Gilbert investigated the reactions of magnets and amber and
discovered other objects can be made "electric."
Gilbert said that amber acquired what he called
"resinous electricity" when rubbed with fur. Glass,
however, when rubbed with silk, acquired what he termed
"vitreous electricity."
He thought that electricity repeled the same kind and
attracts the opposite kind of electricity. Gilbert and other
scientists of that time thought that the friction actually
created the electricity (their word for the electrical charge).
In 1747, Benjamin
Franklin in America and William Watson in England both
reached the same conclusion. They said all materials possess a
single kind of electrical "fluid." They didn't really
know anything about atoms and electrons, so they called how it
behaved it a "fluid.
They thought that this fluid can penetrate matter freely and
couldn't be created or destroyed. The two men thought that the
action of rubbing (like rubbing amber with fur) moves this
unseen fluid from one thing to another, electrifying both.
Franklin defined the fluid as positive and the lack of fluid
as negative. Therefore, according to Franklin, the direction of
flow was from positive to negative. Today, we know that the
opposite is true. Electricity flows from negative to positive.
Others took the idea even further saying this that two
fluids are involved. They said items with the same fluid attract
each other. And opposite types of fluid in objects will make
them repel each other.
All of this was only partially right. This is how scientific
theories develop. Someone thinks of why something occurs and
then proposes an explanation. It can take centuries sometime to
find the real truth. Instead of electricity being a fluid, it is
the movement of the charged particles between the objects... the
two objects are really exchanging electrons.
READ MORE ABOUT IT!
Here are some additional websites to check out.
|
