static electricity. what is static electricity the buildup of electrical charges in one place....
TRANSCRIPT
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
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