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

BEFORE 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. 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 Place an “X” in the appropriate box: +ve and -ve +ve and neutral +ve and +ve -ve and neutral -ve and –ve Neutral and neutral

Attract Repel Neither X Place an “X” in the appropriate box: +ve and -ve X +ve and neutral +ve and +ve -ve and neutral -ve and –ve Neutral and neutral

Rules of static electricity Objects with like charges repel, but objects with unlike charges attract 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 do both, without touching the object - it is an action-at-a-distance force. Laws of Static Charge Like charges repel Opposite charges attract Neutral objects are attracted to charged objects See pages 258 - 259

Charging Objects Charging By Conduction Charging By Induction 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 charge movement and separation in the in the neutral object (like charges repel!) See pages 259 - 260