Static electricity and atoms
You walk across the rug, reach for the doorknob and .... you get a shock.
Or, you come inside from the cold, pull off your hat and...... all your hair
stands on end. What is going on here, you might wonder.
The answer is Static Electricity.
To understand what static electricity is, we have to learn a little bit
about the nature of matter. 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 put one half away. Take the other half and 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. This
is called an atom. If you divided it further into smaller pieces, it would
no longer be gold.
Different atoms
Everything around us is made of atoms. Scientists so far have discovered
115 different kinds of atoms. Everything you see is made of different
combinations of these atoms.
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 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 centre of the atom, like the sun in the centre
of the solar system. The electrons orbit the nucleus like the planets move
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.
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.
The protons and neutrons in the nucleus are tightly held together.
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
looses 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 material hold their electrons very tightly. Electrons do not move
through them very well. They are called insulators. Plastic, cloth, glass
and dry air are good insulators. Some material have 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 material, and
are both insulators, electrons may be transferred (or moved) from one to the
other. The more vigorous the rubbing, the more electrons move, and the
larger the charges built 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.
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.
Positive charge
So what does all this have to do with shocks? Or hair full of static?
When you take off your wool hat, it rubs against your hair. Electrons move
from your hair to the hat. Now each of the hairs has the same positive
charge. Remember, things with the same charge repel each other.
So the hair strands try to move away from each other. The farthest they
can get is to stand up and away from all the other hair.
If you walk across a carpet, electrons move from the rug to you. Now you
have extra electrons.
Touch the doorknob, the electrons move from you to the knob and you get a
shock.
An experiment for you
You must have seen the flames coming out of burning wood. These flames
are quite colourful. Sometimes they are red, sometimes yellow, blue or
green. But have you ever thought where these colours come from?
First, collect things like salt, caustic soda, baking soda and lime,
which are easily available in your house. Now take a coin and holding it
with the pliers, dip it in water and then insert it into a heap of salt, so
that some salt particles remain stuck to the coin. When you heat the coin
over a spirit lamp, you will see a shining yellow flame. Continue keeping
the coin over the flame till this yellow colour is not visible any more.
Conduct this test with all other materials you have collected, one by one
and note down the colours of the flame against each material. It is quite
possible that in some cases, the colour of the flame might not change, but
in the majority of cases, it would. For example, borax would emit a green-coloured
flame on heating.
It has already been proved by scientists that every element gives out its
own peculiar light on heating. For example, sodium, when heated to a certain
temperature, emits a yellow light. This is the reason why salt (chemical
name - sodium chloride) gave a yellow flame when heated. Similarly, boron
(found both in borax and boric acid) produces a green light.
Now you would not be surprised to see different colours in the flame by
different combustive elements present in the wood. Carry out this experiment
only under adult supervision.
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