Static Electricity
Bonnie and Lee were dressed for the weather as
they walked to school one very cold winter day. As
they entered the school, they noticed that the
hallway lights were out. Lee was right behind
Bonnie when she removed her hat.
Suddenly Lee called out, “Wow! What was that?”
Bonnie asked, “What was what?”
“Your head just lit up like the Fourth of July!” Lee responded. “When you took off your
hat, I saw sparks around your head and I could hear little crackles. Here, let me
straighten your hair, it’s all standing on end.”
Lee reached for Bonnie’s hair. “Crack!” “Ouch! Something just happened that hurt!”
“I felt it, too!” said Bonnie.
Why is Bonnie’s hair acting in this strange manner?
Is it something in the hat? Or in her hair? Or both?
How could the girls study make this phenomenon happen again so they could study it?
Background Information
You walk across the rug and reach for the doorknob. You see sparks and hear crackles, 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? And why does it only seem to happen in the winter? The answer is
STATIC ELECTRICITY. To understand what static electricity is, you have to learn about the
nature of matter, the structure of atoms, and how parts of atoms behave.
PARTS OF AN ATOM and ELECTRICAL CHARGES
Atoms are made up of protons, neutron, and electrons. Each atom has a nucleus in its center
that contains protons and neutrons. The electrons orbit around the nucleus. Protons, neutrons,
and electrons have very unique characteristics. One of these properties is called an electrical
charge. Protons have a positive charge, electrons have a negative charge, and neutrons have no
charge. Normally, each atom has an equal number of protons and electrons. So each positive charge is
balanced by a negative charge. As a result, there is no overall electric force on an atom.
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ELECTRONS CAN MOVE
It is possible for electrons to sometimes leave their atoms. Some materials hold their electrons
very tightly and electrons do not move through them very well. Other materials hold electrons
with less energy, so it is easier for the electrons to be taken from the atom. When this happens,
the atom has more protons than electrons and so has a positive charge. The electrons, on the
other hand, can be held by other atoms which then gives them a negative charge. With enough
energy, electrons can flow through some materials, called conductors. Static electricity is the
imbalance of positive and negative charges. In static electricity, charges build up on an object,
but they do no flow continuously.
Materials like plastic, cloth, glass and dry air do not easily gain, lose, or pass electrons. They
are good insulators. Most metals on the other hand (e.g. silver, copper, gold, and aluminum) are
good conductors.
An object becomes charged only when electrons are transferred from one location to another. If
one object gives up electrons, another object gains those electrons.
Charging By Friction
When two common uncharged objects rub together, some electrons from one object can move
onto the other object. The object that gains the electrons becomes negatively charged, and the
object that loses electrons becomes positively charged. Charging by friction is the transfer of
electrons from one uncharged object to another by rubbing. 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 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.
Charging By Conduction
Charging by conduction is the transfer of electrons from a charged object to another object by
direct contact. Electrons transfer from the object that has the more negative charge to the one
that has the more positive charges. When the hat was removed, the electrons were stripped
from Bonnie’s hat. The negative charge was great enough that some of the electrons jumped
the gap between hat and hair, giving off light and sound as they did so. The remaining
electrons stayed on Bonnie, waiting for the unsuspecting Lee allow them to be discharged.
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Lightning
Lightning is a dramatic example of static electricity. Lighting is a temporary current of electricity
that happens as a result of a large build-up of static charge. It is essentially the same
phenomenon as “static shock,” but it happens on a much larger scale. During thunderstorms,
air swirls violently. Water droplets within the clouds become electrically charged. Electrons
move from areas of negative charge to areas of positive charge and produce an intense spark.
This restores a neutral condition but you see the spark as lighting.
What causes lightning to enter a building or strike a person?
Electrical charges can travel through humans as the current travels to the ground and returns to
the clouds. Lightning can travel through cable and phone lines into a building. It can also enter
through open spaces such as doors and windows. Any metal such as pipes and electrical wires
will provide a path for lightning.
Inquiry Problem Solution
So what does this have to do with sparks and crackles? Or hair standing on end? When Bonnie
took off her wool hat, it rubbed against her hair. Electrons moved from her hat to her hair. When
electrons move from an area of negative charge to areas of positive charge they may produce
sparks and crackles as some of the electrons “jump” back through the air from the hat to the
hair.
Each of the hairs now has the same charge. 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. Bad hair day! Dry air is more common in the winter. This is why it
does not happen every time Bonnie wears a hat.
When Lee went to touch Bonnie’s hair, the remaining electrons were conducted to her – giving
her a very mild electric shock.
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