Lect09

# Lect09 - Physics 213 Sept 21 2006 Physics 213 Sept 21 2006...

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Unformatted text preview: Physics 213! ! Sept. 21, 2006 Physics 213! ! Sept. 21, 2006 Physics II: Heat & Electromagnetism today-- 1. Electric field of continuous charge dist. 2. Electric potential 3. Electric field lines 4. Electric dipoles Electric potential energy U Electric potential V ! 9.1 ! 9.2 Physics 213! ! Sept. 21, 2006 Physics 213! ! Sept. 21, 2006 Recall: electric field of a point charge, represented by an vector at each point in space, looks like r r E( r ) r Electric field of a point charge, represented by field lines-- r r E( r ) r r q q r r ! 9.3 ! 9.4 Physics 213! ! Sept. 21, 2006 Physics 213! ! Sept. 21, 2006 Properties of field lines: 0.! They're not vectors! 1.! They point in the direction of the electric field. (precisely: the electric field is tangent to the field line.) r 2.! Spacing of field lines !1 E . 3.! # of field lines q charge +2q: charge +q: 4.! Field lines, like E field, point away from "+" charges and toward "-" charges 5. Field lines never cross 6. Field lines never begin or end except on charges 7. Field lines never make closed loops if the field is static (not time varying) charge q: r ! 9.5 ! 9.6 Physics 213! ! Sept. 21, 2006 Physics 213! ! Sept. 21, 2006 two positive charges +q an electric dipole (+q and q): (+2q and q): ! 9.7 ! 9.8 Physics 213! ! Sept. 21, 2006 Physics 213! ! Sept. 21, 2006 Electric dipole-- +q d q A) An electrically neutral dipole is placed in an external electric field. In which situation In a uniform electric field: +q d r F+ r E r F! q (s) is there zero net force on the dipole? 1. (a) 2. (c) 3. (a) and (c) 4. (c) and (d) 5. none of the above ! 9.9 ! 9.10 ...
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Lect09 - Physics 213 Sept 21 2006 Physics 213 Sept 21 2006...

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