Static Electricity

What is Static Electricity• The buildup of electrical charges in one place.• Static = charge does not move or flow• (usually a temporary condition).• Can be detected by an electroscope.

Examples of static electricity:• Rubbing a balloon on your hair• Walking across carpet• Clothes tumbling in dryer

• What do these have in common?

Friction!!!!

Creating Static Charges

• Static charges result when some charges are transferred from one object to another by friction

• Which charges are easily removed? – Recall structure of the atom.

Recall from Chemistry

• Electrons (-) are on the outside of the atom so they can be easily removed, while protons (+) are held firmly in the nucleus

• Protons & Neutrons

• Electrons

Two Types of Charge• Electrons can be transferred by friction, but protons

cannot– Transferring protons would create a new element!

• LOSING electrons gives an object a POSITIVE charge

• GAINING electrons gives an object a NEGATIVE charge

• NOTE: When one object loses, another must gain - electrons can’t be created or destroyed

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.

BEFORE

AFTER

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”

Conduction

• Conduction = direct transfer of charge

• Eg: walk across carpet and touch a doorknob shocking!

• Electrons are stripped from the carpet and you gain a net –ve charge

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

Attract Repel Neither

+ve and -ve

+ve and neutral

+ve and +ve

-ve and neutral

-ve and –ve

Neutral and neutral

Place an “X” in the appropriate box:

Attract Repel Neither

+ve and -ve X

+ve and neutral

X

+ve and +ve X

-ve and neutral

X

-ve and –ve X

Neutral and neutral

X

Place an “X” in the appropriate box:

Rules of static electricity

1. Objects with like charges repel, but objects with unlike charges attract

2. Charged objects attract neutral objects

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 have different attractions to the e-

• The stronger one will take e- away from weaker one and static charges build up

Uses of static electricity

• Trapping particles in smokestacks of factories

• Applying grit to sandpaper

• Spray painting mesh (e.g. chain link fence)

• Powder coating

The leaves are repelled by the like charge upon them.

7.2 Electric Force--Summary

• Force is a push or pull - electric force can doboth, without touching the object - it is anaction-at-a-distance force.

Laws of Static Charge• Like charges repel• Opposite charges attract• Neutral objects are

attracted to chargedobjects

See pages 258 - 259

Charging Objects

Charging By Conduction• Charging through direct contact• Extra electrons will move to a location

where there is less of them

Charging By Induction• Bringing a charged object nearby

a neutral object will cause chargemovement and separation in thein the neutral object

• (like charges repel!)

See pages 259 - 260