New Star Software Collection/NSS_Collection.iso/3-251 oo2 english program/1.ima/RR.ZIP/PELECTRI.SEQ

Text File | 1991-06-30 | 4.1 KB | 79 lines

Thales was a Greek philosopher who lived more than 2,000 years
ago. He noticed that when he rubbed fur and amber together, the
amber attracted loose fur and other substances. These stuck to
the amber. Five hundred years ago, an English scientist, called
William Gilbert, noticed the same mysterious force. He decided
to call it electricity from the Greek word elektron, meaning
"amber." Scientists have learned a lot about electricity in the
last few centuries.

They now understand that the structure and behaviour of atoms
account for the phenomena observed long ago by Thales and
Gilbert.

Every substance in our world is composed of atoms, which can be
considered the smallest units of matter. The term element
describes the general group of atoms of a particular type. There
are only about 100 different elements, but they combine in an
almost infinite number of ways to form molecules of all the
different forms of matter that we are familiar with. For
example, a molecule of water (H20) is made up of three
atoms--two of hydrogen and one of oxygen.

Each element has its own particular atomic structure. However,
to understand the differences between these structures, we must
first know what an atom is. An atom consists of several
particles: one or more protons in a nucleus surrounded by one or
more orbiting electrons. Protons are much heavier than electrons
and have a positive electrical charge. The electrons have a
negative charge. They are held in orbit around the nucleus by
the force of their attraction to the protons. (Particles with
like charges--both negative or both positive--repel each other,
whereas particles with unlike charges attract each other.) A
third kind of particle--the neutron--is present in the atoms of
all elements except hydrogen. Neutrons are a part of the
nucleus, and they carry no charge.

Atoms vary in complexity. The hydrogen atom, with its single
proton and single electron, is the simplest of all. An atom of
plutonium, on the other hand, is far more complex; it contains
94 protons and 94 electrons. An element's atomic number is
always the same as its number of protons. Thus, hydrogen has the
atomic number 1, and plutonium has the atomic number 94. In its
stable, or uncharged, state, an atom has as many protons as
electrons. However, its electrons can be drawn out of their
orbits by outside forces (such as the friction produced by
rubbing). When this occurs, the atom becomes positively charged
because it now has more protons than electrons. The "free"
electrons, which have left their orbit, may now attach
themselves to other atoms. Atoms with an excess of electrons are
said to be negatively charged.

When you comb your hair on a dry day, your hair loses electrons
and becomes positively charged. The comb gains electrons from
your hair and becomes negatively charged. The comb is generating
static electricity. As your hair loses electrons and becomes
positively charged, it crackles, stands up and tries to stick to
the comb. Because the comb has gained an excess of electrons
(from your hair), it is now negatively charged. Thus, positively
charged substances near it, like small pieces of paper and hair,
will be attracted to the comb and even stick to it.

Pieces of paper, hair, and fur are all substances that lose
their electrons easily and therefore usually have a positive
charge. The electrons of the amber and those of the comb are
firmly in place, while those of the items attracted to them are
not. When Thales rubbed fur and amber together, some of the
electrons in the fur atoms were pulled out of their orbits. They
attached themselves to the amber, giving it an excess of
electrons. The amber, now negatively charged, attracted the
positively charged atoms in the fur, which seemed to stick to
the amber. This movement of electrons from one atom to another
is the basis of how electricity is made.

If we are now able to explain what Thales and Gilbert observed,
it is only because scientists have spent centuries studying the
phenomenon of electric force. Everything that we now know about
electricity is based on an understanding of the structure and
behaviour of atoms.