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Static ElectricityChapter 20
Electric ForceSection 20.1
ElectrostaticsElectric Statics that can be
collected and held in one place.
Charged ObjectsObject that exhibits
electric interaction after rubbing is said to be charged◦Like charges: Repel
each other◦Opposite charges:
Attract each other◦Types of charge:
Matter contains both charges
A Microscopic View of ChargeAll objects contain
light, negatively charged particles◦Neutral object: positive
charge of nucleus equals the negative charge of surrounding electrons
◦Separation of charge: Occurs when two objects are rubbed together
Conductors and InsulatorsElectric
Conductor◦ Material that
allows charges to move easily
◦ Metals (ie: copper, iron, silver, gold)
Electric Insulator◦ Material through
which charge will not move easily
◦ Glass, dry wood, plastics, rubber, cloth, and dry air
Electric ForceSection 20.2
Forces on Charged Bodies There are two kinds of charges:
◦ Positive and Negative Charges exert forces on other charges at a
distance. The force is stronger when the charges are closer Like charges repel; opposite charges attract.
ElectroscopeDevice used to
determine charge.◦ Metal knob
connected by a metal stem to two thin, lightweight pieces of metal foil.
Charging by Conduction
Charging a neutral body by touching it with a charged body◦ Leaves spread apart it electroscope is
positive
Separation of Charge on Neutral Objects
Neutral object will have charges separate. ◦ Neutral object will be attracted to
the charged object.
Charging by InductionCharging an object without
touching ◦ Single object can be charged by
induction through grounding
Coulomb’s LawForce depends on
distance◦ F = 1/r2
Force depends on charge
◦ F= qAqB
Coulomb’s Law
◦ F= qAqB/ r2
Elementary Charge◦ Magnitude on electron:
1.60 X 10 -19 C◦ 1 C = 6.24 X 1018
electrons
Coulomb’s Law
Force in Newtons (N)
Coulomb’s constant: 9.0 X 109 Nm2/C2
Distance between ChargesIn Meters (m)
Charge in Coulombs (C) of object 1
Charge in Coulombs (C) of object 2