estatics1 - Properties of Electric Charges Two types of...

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1 Electrostatics 1 Electric Forces & Electric Fields Properties of Electric Charges Two types of charges exist ositive and negative pos t e a d egat e Like charges repel and unlike charges attract one another Nature’s basic carrier of positive charge is the proton Protons do not move from one material to another because they are held firmly in the nucleus Nature’s basic carrier of negative charge is the electron aining or losing electrons is how an object becomes charged Gaining or losing electrons is how an object becomes charged Electric charge is always conserved (never created, only exchanged) Objects become charged because negative charge is transferred from one object to another Characteristics of Fundamental Charges electric charge is quantized - that is, charge mes in units of the fundamental charge comes in units of the fundamental charge e e = 1.6 x 10 -19 C unit is C : Coulombs Materials: Conductors & Insulators Conductors are materials in which the electric charges move freely in response to an electric force Metals : Copper, aluminum and silver are good conductors added charge redistributes itself quickly over conductor sulators re materials in which electric arges Insulators are materials in which electric charges do not move freely Glass and rubber are examples of insulators When insulators are charged by rubbing, only the rubbed area becomes charged
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2 Electric Charges and Forces, Part I The Charge Model Electric Charges and Forces, Part II The Charge Model
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3 Visualizing Charge Charges on an insulator do not move. g Charges on a conductor adjust until there is no net force on any charge. We call this electrostatic equilibrium . Charging by Conduction (Contact) A charged object (the rod) is placed in contact with another bject (the sphere) object (the sphere) Some electrons on the rod can move to the sphere When the rod is removed, the sphere is left with a charge The object being charged is always left with a charge having the same sign as the object doing the charging Charging by Induction (no contact) When an object is connected to a conducting wire or pipe buried in the earth, it is said to be rounded , g Start with an uncharged sphere A negatively charged rubber rod is brought near an uncharged sphere Charging by Induction, 2 The charges in the sphere are redistributed Some of the electrons in the sphere are repelled from the electrons in the rod The region of the sphere nearest the negatively charged rod has an excess of positive charge because of the migration of electrons away from this location A grounded conducting wire is connected to the sphere Allows some of the electrons to move from the sphere to the ground
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4 Charging by Induction 3 The wire to ground is removed, the sphere is left with an excess of induced positive charge the positive charge on the sphere is evenly distributed due to the repulsion between p the positive charges
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This note was uploaded on 03/22/2011 for the course MAC AEPH114 taught by Professor Knutt during the Spring '11 term at McGill.

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estatics1 - Properties of Electric Charges Two types of...

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