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Static Electricity

Static Electricity

• What is Electricity ?

• What is Static Electricity ?

• difference between them ?

Static Electricity• What is Electricity

Electricity is a form of energy. Electricity is the flow of electrons. All matter is made up of atoms, and an atom has a center, called a nucleus. The nucleus contains positively charged particles called protons and uncharged particles called neutron

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+

–

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Atom Nucleus

Static Electricity

• What is Static Electricity

Static electricity occurs when there is a build up of electric charge on the surface of a material.

It is called static electricity because the charges don’t move.

The electricity we use everyday involves moving charges.

Static = Charge does not move or flow

Two kinds of charges• After being rubbed, a plastic ruler can attract paper scraps.

Ruler carries electric charge.

It exerts electric force on paper.

This charging method is called charging by friction.

The interaction between static electric charges is called electrostatics

Static Electricity

Static Electricity

Where do charges come from?.

If electrons = protons ⇒ neutral

If electrons > protons ⇒ gaining electrons, negative charge

If electrons < protons ⇒ losing electrons, positive charge

Static ElectricityWhere do charges come from?

When a balloon rubs a piece of wool...

electrons are pulled from the wool to the balloon.

The balloon has more electrons than usual.

The balloon: – charged, The wool: +chargedwool

– +++

+

+

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Static Electricity

Where do charges come from?

Rubbing materials does NOT create electric charges.

It just transfers electrons from one material to the other.

Static Electricity

Examples of static electricity:

Rubbing a balloon on your hair

Walking across carpet

Clothes tumbling in dryer

What do these have in common?

Friction!!!!

Static Electricity

Combing transfers

electrons from the hair

to the comb by friction,

resulting in a negative

charge on the comb and

a positive charge on the

hair.

Static Electricity

Induced charge

• Charged and neutral objects (not touching) are attracted because electrons move in the neutral object.

• Electrons move toward a +ve charged object and away from a –ve charged one.

This is called “induced charge”

Static Electricity

Conduction

Conduction = direct transfer of charge

Example : walk across carpet and touch a doorknob shocking!

Electrons are stripped from the carpet and we gain a –ve charge

When you touch the doorknob, electrons jump onto it :electrical discharge

Static Electricity

Rules of static electricity

Objects with like (same) charges repel, but

objects with unlike charges attract.

Charged objects attract neutral objects

Static Electricity

Does friction always create static charge?

Different materials have different strength of attraction for electrons

If two objects of the same material are rubbed, no static charge forms (equal number of electrons transfer each way)

If two different objects are rubbed, they will have different attraction to the electrons. The stronger one will take electrons away from weaker one and static charges build up

Static Electricity

Uses of static electricity

Dust removal (Pollution Control)

Photocopy (Xerography)

Car Painting

Static Electricity

Effect of Materials on Static Electricity Materials are listed below according how well they create static electricity

when rubbed with another material, as well as what charge the material will possess.

Become positive in charge

Materials that gain a positive (+) electrical charge ( or tend to give up electrons)

Dry human skin Greatest tendency to giving up electrons and becoming highly positive (+) in charge

Leather

Glass The glass on your TV screen gets charged and collects dust

Static Electricity

Effect of Materials on Static Electricity

Human hair "Flyaway hair" is a good example of having a moderate positive (+) charge

Nylon

Wool

Lead A surprise that lead would collect as much static electricity as cat fur

Cat fur

Silk

Aluminium Gives up some electrons

Paper

Static Electricity

Effect of Materials on Static Electricity

Neutral

There are very few materials that do not tend to readily attract or give up electrons when brought in contact or rubbed with other materials.

Materials that are relatively neutral

Cotton Best for non-static clothes

Steel Not useful for static electricity

Static Electricity

Effect of Materials on Static Electricity

Become negative in charge

Materials that gain a negative (−) electrical charge

Wood Attracts some electrons, but is almost neutral

Nickel, Copper Copper brushes used in Wimshurst electrostatic generator

Gold, Platinum Attract electrons almost as much as polyester

Polyethylene (Scotch Tape)

Pull Scotch Tape off surface and it will become charged

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