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Static Electricity - Part I |
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On a cold dry morning, have you ever felt that while removing a pullover, the hair on your hands stand up? Take a few pieces of paper. Take a plastic comb and comb your hair fast. Your hair has to be dry. Then hold the comb close to the papers. The papers will tend to get attached to the comb. What is making the paper stick to the comb? Well, all these phenomena are due to transfer of charges from one object to the other. The study of static charges is called static electricity. All of us know that matter is made up of atoms. Atoms in turn have
electrons and protons (and neutrons). Electrons are electrically negative
and the protons are electrically positive charges. Like charges repel each
other where as unlike charges attract each other. The unit of charge is a
coulomb (C) and one electronís charge is as follows : What we will
study in this chapter : 1. How static electricity is generated? 1.
How static
electricity is generated? We
saw in the experiment with a plastic comb that the comb gets charged when
you vigorously comb your dry hair. The electrons from your hair get
dislodged and get on the surface of the comb.
The plastic comb gets negatively charged and your dry hair will
become positively charged. Pieces of paper get attracted to the charged
plastic comb. The reason for the paper to get attracted is because charges
in the paper get polarized or induced. The detail mechanism is explained in
the next section. A
question might arise in your mind : what happened to your dry hair which had
become positively charged by having electrons transferred to the plastic
comb? The charges built up have to be earthed. The earth is considered to be
a reservoir of electrons, so the electrons from the earth travel up, through
your body. If the charges are not earthed soon, you may get a sharp shock if
you touch anything metallic. The sharp shock is due to charges built up in
your body being electrically neutralized by the electrons hopping from the
metal you have touched. Static
electricity is observed only in insulators. As far as electrical properties
are concerned, materials can be divided into two groups : conductors and
insulators. In
conductors, the electrons move around freely. Most metals are conductors. In
our electrical wiring the metal threads are either copper or aluminum. In
metals, the electrons are bound to many atoms at the same time. This type of
bonding is either ionic or metallic bonding.
That is why metals are known to have a îseaî of electrons in
them. These electrons can flow easily, that is the reason why metals become
good conductors of electricity. If you
rub a metal, charges will build up, but they get nullified or earthed
quickly. In
insulators, the number of electrons moving freely is not as many as in
metals. If you observe the electron binding in an insulator, they are
usually covalent bonded. Most of the man made materials made out of
hydrocarbons like plastic, nylon, etc are insulating. From naturally occurring substances, rubber, and wood are good
examples of insulators. Insulators are also known as bad conductors. Now
the question is how do insulators develop static electricity? In the
insulators the electrons are tightly bound and are not as ìfreeî to move around as in metals. But there are some materials,
where there may be residual electrons that are not tightly bound. In that
case, the loosely bound residual electrons are easy to be dislodged from the
material. There may be locations in the material where electrons are not
tightly bound. These electrons can jump off from one material and get
attached to any other material close to it. It has to be remembered that the
electrons jump off only on rubbing the comb vigorously on dry hair.
The
phenomena of static electricity will not occur on wet hair. This is because
water conducts electricity. Hence the comb will not develop static
electricity.
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