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Electrostatics The study of electrical forces at rest. Electrical Forces and Charges. Arise from particles in atoms Protons in nucleus attract electrons in orbit around the nucleus. Atom Basics. Charge. The strength of charged particles is measured in coulombs .
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Electrical Forces and Charges • Arise from particles in atoms • Protons in nucleus attract electrons in orbit around the nucleus. • Atom Basics
Charge • The strength of charged particles is measured in coulombs. • An electron and a proton have the same magnitude of charge, just opposite signs. • An electron has a charge of –1.602x10–19C. • A proton has a charge of +1.602x10–19 C.
Conservation of Charge • The electrons are not created or destroyed, they are simply transferred from one object to another. • The overall amount of electrical charge stays the same. • Also, all net charges will be a multiple of the charge on one whole electron—there are no fractional electrons!
Transfer of Charge • By FRICTION, when electrons are transferred by friction from one object to another. • By CONDUCTION, when electrons are transferred from one object to another by direct contact without rubbing. • By INDUCTION, when electrons are caused to gather or disperse by the presence of nearby charge. • Electroscope Simulation
Conductors permit electrons to flow freely from atom to atom and molecule to molecule permit charge to be transferred across the entire surface of the object Conductors allow for charge transfer through the free movement of electrons. Insulators materials which impede the free flow of electrons from atom to atom and molecule to molecule The particles of the insulator do not permit the free flow of electrons; subsequently charge is seldom distributed evenly across the surface of an insulator Conductors vs. Insulators
Increasing Conductivity Ability • Rubber • Glass • Wool • Dry Air • Silicon • Germanium • Salt Water • Carbon • Mercury • Iron • Aluminum • Copper • Silver Increasing Conducting Ability Insulators Semi-Conductors Conductors
Like charges repel; opposite charges attract. Like charges repel And Unlike charges attract And that is that!
Coulomb’s Law The electrical force between two charges varies directly as the product of the charges and inversely as the square of the distance between them.
Coulomb’s Law F = force (N) q = charge (C) d = distance (m) k = 9.0 x 109 N m2 / C2
Example Coulomb’s Law A negative charge of -2.0 x 10-4 C and a positive charge of 8.0 x 10-4 are separated by 0.30 m. What is the force between the two charges? Is it attractive or repulsive?