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Static electricity is the build-up of electrical charges on the surface of some object or material. Static electricity is usually created when materials are pulled apart or rubbed together, causing positive (+) charges to collect on one material and negative (-) charges on the other surface.

Results from static electricity may be sparks, shocks or materials clinging together.

Questions you may have include:

•  What is static electricity?

• How is it created?

•  What effects does static electricity have?

This lesson will answer those questions.

Description of static electricity
Static electricity is the accumulation of electrical charges on the surface of a material, usually an insulator or non-conductor of electricity. It is called “static” because there is no current flowing, as there is an alternating current (AC) or direct current (DC) electricity.

Typically, two materials are involved in static electricity, with one having an excess of electrons or negative (-) charges on its surface and the other material having an excess of positive (+) electrical charges. Atoms near the surface of a material that have lost one or more electrons will have a positive (+) electrical charge.

If one of the materials is an electrical conductor that is grounded, its charges will drain off immediately, leaving the other material still charged.

Cause of static electricity
Static electricity is usually caused when certain materials are rubbed against each other—like wool on plastic or the soles of your shoes on the carpet. It is also caused when materials are pressed against each other and pulled apart.

The process causes electrons to be pulled from the surface of one material and relocated on the surface of the other material. It is called the tribo-electric effect or tribo-electric charging.

The material that loses electrons ends up with an excess of positive (+) charges. The material that gains electrons ends up an excess of negative (-) charges on its surface.

Dry air preferred
Static electricity is formed much better when the air is dry or the humidity is low. When the air is humid, water molecules can collect on the surface of various materials. This can prevent the build-up of electrical charges. The reason has to do with the shape of the water molecule and its own electrical forces.

Rainstorms
But when there is extreme turbulence among water drops, such as in a thunderstorm cloud, static electric charges can build up on the water drops.

Benjamin Franklin showed that static electricity in created in a thunderstorm cloud by flying a kite in a storm. He detected the static electricity by seeing the hairs on the kite string stand on end and by creating a static electric spark with a metal key. This was dangerous experiment, and Franklin was lucky not to be killed.

(For more information, see the biography of Ben Franklin’s life.)

Properties or effects of static electricity
Static electricity can cause materials to attract or repel each other. It can also cause a spark to jump from one material to another.

Attraction
Rub a balloon on a wool sweater.

The balloon collects negative electrical charges on its surface and the wool collects positive charges. You can then stick the balloon to the wall, which does not have an excess of either charge.

The balloon will also stick to the wool, although the charges may jump back to the original material in a short time.

You can also run a comb through your hair to charge the comb with static electricity. The comb can then be used to attract neutral pieces of tissue.

Repulsion
Comb your hair on a dry day or after using a hair drier. The plastic comb collects negative charges from the hair, causing the hair to have an excess of positive charges. Since like charges repel, the hair strand will tend to push away from each other, causing the “flyaway hair” effect.

Sparks
If there are enough positive (+) electrical charges on one object or material and enough negative (-) charges on the surface of the other object the attraction between the charges may be great enough to cause electrons to jump the air gap between the objects.

Once a few electrons start to move across the gap, they heat up the air, such that more and more will jump across the gap.

This heats the air even more. It all happens very fast, and the air gets so hot that it glows for a short time. That is a spark.

The same thing happens with lightning, except on a much larger scale, with higher voltages and current.

Summary
Rubbing certain materials together can cause the build-up of electrical charges on the surfaces. Opposite charges attract and same charges repel. Either charge will be attracted to something of neutral charge.

Sparks are an extreme case of electrons being attracted to an object that has a positive charge and jumping across an air gap, thus heating the air for a fraction of a second.

Take this Mini-quiz to check your understanding of the lesson material.

Top of Form
1. Where do most static electric charges collect?
A- In a copper wire
B- On the surface of a non-conductor
C- In a spark

2. Which of the following will usually create static electricity?
A-  a wet rag on a plastic comb
B- Rub a coin with a plastic comb
C- Rub a plastic comb with some rabbit fur

3. What can cause electrons to jump across a gap and cause a spark?
A- The force from a large positive charge on the other side of the gap
B- Lightning causes many things to happen
C- Heating up the gap

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