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Unformatted text preview: Electricity and Magnetism Coulombs Law: F = k*(q 1 q 2 )/r 2 A shell of uniform charge attracts or repels a charged particle that is outside the shell as if all the shells charge were concentrated at its center If a charged particle is located inside a shell of uniform charge, there is no net electrostatic force on the particle from the shell Electric Fields: E field = F /q =k(q)/r 2 (units: N/C) (for a point charge) The direction of E is the direction of the force on a (+) charge E field lines extend away from (+) charges and toward (-) charges F =q E : Force, F, same direction as E if q is (+), opposite if q is (-) Gausss Law : Gausss Law relates the E fields at points on a closed Gaussian surface and the net charge enclosed by that surface(only interior affects flux) electric = E*dA = Ecos dA (Electric Flux thru a Gaussian Field) ((N*m 2) /C) E field and Area vector point in same direction, parallel The electrical flux thru a Gaussian surface is proportional to the net # of E field lines passing thru that surface E * dA =q/ EA=q/ If an excess charge is placed on an isolated conductor, that amount of charge will move entirely to the surface of the conductor. None of the excess charge will be found with in the body of the conductor Electric Potential: U = electric potential energy W=work done by electrostatic force U = U f-U i = -W f = -F* d s F=q *E field U=-q *E* d s Electric Potential Difference : V= V f-V i = -W/q = U/q 0 = -E* d s V=k(q)/r U=qV *note: V is scalar, E is vector Capacitance q=CV (C: Farad) C=q/V= (A/d) (for parallel plate capacitor) C=Q/EMF Series: Parallel: V T = V 1 + V 2 + V 3 V T = V 1 = V 2 = V 3 q T = q 1 = q 2 = q 3 q T = q 1 + q 2 + q 3 1/ C T = 1/C 1 + 1/C 2 + 1/C 3 C T = C 1 + C 2 + C 3 C T = (C 1 C 2 )/(C 1 + C 2 ) 1/ C T = 1/C 1 + 1/C 2 =2/C so C=2C T U=(1/2)(q)*V=(1/2)CV 2 =q 2 /2C (U = potential energy) u =(1/2) E 2 =U/(A*d) ( u = Energy Density) Maxwells Equations: E* d A=q/ E* d s= - d B /d t B* d A=0 (closed surface) B* d s= ( i + ( d E /d t))----When in series, the bulb with the higher resistance dissipates more power.----When in series, the bulb with the higher resistance dissipates more power....
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