1Bweek4 - Physics 1B Notes Week 4 Spring 2010 Electricity...

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1 Physics 1B Spring 2010 Electricity and Magnetism Notes Week 4© Walter Gekelman This is it folks, these four equations capture all of electricity and magnetism. We will spend the rest of the quarter an half of next studying what they mean! Integral Form : Differential form: E ˆ n dA = Q in ε 0 surface B surface ˆ n dA = 0 E line d l = t B ˆ n dA area B line d l = μ 0 i + 0 0 t E ˆ n dA area Here i is current, j is current density, Q is charge, ρ is charge density and E and B are electric and magnetic fields. It will take these courses to explore what these equations mean and what some of their solutions are. These are Maxwell’s equations and date back to the late 1800’s. Note two vector identities make this all possible: ∇ × A ( ) ˆ ndA = A d l A ( ) dV = A ˆ ndA

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2 First a bit about history: Gilbert in the year 1570 took a thin “sensitive” arrow on a stalk and rubbed it with many things including fur, diamonds, opals, rock crystal. It then turned when it seemed to be attracted by other objects that were rubbed. Otto Von Guericke in the 1660’s used a ball of sulfur and rubbed it against himself (or a cat) and was able to put large amounts of charge on it. He also discovered electrical forces could be attractive or repulsive Stephen Gray (1700) Found the “electric fluid” moved through metals and that an electrified object could be discharge by attaching it to the earth. He deduced that metal could not be electrified because the charge would rapidly pass through it and go somewhere else.
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1Bweek4 - Physics 1B Notes Week 4 Spring 2010 Electricity...

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