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PHYSICS 212 Electricity and Magnetism. 1. Electric Fields. Fundamental properties of electric charge Charging by induction and conduction Coulombs law and the electric force Electric fields Electric field lines Problems / Vectors. Charge Conservation. Experiments show that.
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PHYSICS 212 Electricity and Magnetism 1. Electric Fields • Fundamental properties of electric charge • Charging by induction and conduction • Coulombs law and the electric force • Electric fields • Electric field lines • Problems / Vectors
Charge Conservation Experiments show that • Electric charge cannot be created nor destroyed • CONSERVATION OF CHARGE • Total charge of an object is always an integer multiple of a basic charge “e” • CHARGE QUANTIZATION
Types of Charge • Two types of charge • Named + and - • Like charges repel • Unlike charges attract • Repulsion and attraction are FORCES
Coulombs Law • The force between charges is given byCOULOMBS LAW
Meaning of Symbols • Coulombs constant • Unit vector pointing from charge 1 to charge 2 • The distance between the charges • The force exerted on charge 2 by charge 1
Atomic Structure • Atoms = • Nucleus • is very small less than 10-15 m in diameter, but heavy • Contains protons and neutrons • plus • Electrons • Diameter approx. 10-10 m • are very light but make up the volume of the atom
Materials • Materials are atoms bound together by electrons • Electrons are on the outside • Produce the quality of “Solidness” • Different materials hold their electrons with different forces • Rubbing one material on the other displaces electrons • one material becomes positive the other negative
Charging by induction Charging by Induction
Charging by Conduction Charging by conduction - - - + + + - - - + + + + + + + + + + + + + + + + - + + + + - + - + + + + - + + - + + - + + +
Force due to Many Sources • at a point r • The electric Force due to many point charge sources on a charge q • is the vector sum of all forces due to source charges
Diagram of Many Sources F F1 Q1 q Q2 F2 r F3 Q3
Force Due to Continuous Source • The Electric Force due to a continuous distribution of point charge sources: • A charged solid • at a point r on a charge q • is the vector integral of all forces due to the source charges
Diagram of Continuous Source F q Q r dF
Electric Field The Electric Field is the Force per unit charge
Meaning of Symbols • at a point r • The Electric Field due to many point charge sources • is the vector sum of all fields due to source charges
Diagram of Field due to Point Sources E1 Q1 E E2 Q2 r E3 Q3
Electric Field Lines Electric Field lines are lines that have Electric Field vectors as tangent lines at each point.