Ch 23 Notes

# Ch 23 Notes - Electric Charge Two independent...

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1 Electric Charge • Two independent quantities--positive (+) and negative(-) • Charges of the same sign repel one another and charges with opposite signs attract one another • Net charge is conserved in an isolated system • Charge is quantized—comes in integer multiples of e =1.602x10 -19 coulombs (C) Electric Forces Materials • Electrical conductors—many of the electrons are free to move within the material • Insulators—all of the electrons are bound to atoms—none can move. • Semiconductors—number of free electrons free to move somewhere between that of an insulator and of a conductor Charging by Induction

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2 Charging by Induction, 2 Charge Rearrangement in Insulators Coulomb’s Law • The electrical force between two stationary charged particles is – inversely proportional to the square of the separation r between the particles and directed along the line joining them – proportional to the product of the charges, q 1 and q 2 , on the two particles – attractive if the charges are of opposite sign, repulsive if the charges are of like sign – conservative
3 Mathematical Form of Coulomb’s Law Vector equation! 12 12 2 ˆ e qq k r = Fr •SI unit of charge : Coulomb (C) k e = 8.9875 x 10 9 N.m 2 /C 2 = 1/(4 π ε o ) o = 8.8542 x 10 -12 C 2 / N.m 2 Coulomb's Law, Notes • Remember the charges need to be in coulombs e is the smallest unit of charge • except quarks e = 1.6 x 10 -19 C – So 1 C needs 6.24 x 10 18 electrons or protons • Typical charges can be in the μ C range • Remember that force is a vector quantity Hydrogen Atom Example • The electrical force between the electron and proton is found from Coulomb’s law •|F e |= (k e q e

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Ch 23 Notes - Electric Charge Two independent...

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