Page 1 of 3 10/11/2009 M.Dubson PHYS1120 Notes ©University of Colorado at Boulder PHYS1120 Exam II review Things to remember for PHYS1110: algebra, trig (sin, cos, ..) vector math, especially vector addition, Fnet = ma problems, free-body diagrams Exam I Material : E-fields, Gauss's Law Chapter 23 Voltage = Electric Potential Definition of voltage: fof qiUV E drq , of qU q V V E x ( if E = constant and Ex ) , xdVEdx Voltage is electrical height, E-field is slope if rE, V0 , equipotential lines Voltage due to a point charge Q: kQV(r)r Voltage due to many charges: iiiiikQkdqV(r) Vrr Work done by external agent to move charge q through a voltage difference V = ext of qW U q V . If charge q falls through a voltage difference V, KE PE q V Units of electron volts (eV). Ch.24 Capacitors capacitance QCV E hi V lo V +Q –Q E V = V dPage 2 of 3 10/11/2009 M.Dubson PHYS1120 Notes ©University of Colorado at Boulder area A d R I V hi V lo V in series: R1 R2 = Rtot = R1 + R2 R1 R2 = in parallel: C depends only on size and shape: oACd Adding capacitors in series and parallel. stored energy = 221 1 1 QU QV CV2 2 2 C energy per volume = 2oU1uEvolume 2. Ch.25, 26 Current and Circuits dQIdt, dIJ n q vA (where n = #carriers/volume, vd = drift speed) 1J E E , = resistivity = measure of internal friction, depends on composition Ohm's Law: V I R (where R = constant) Resistance of a resistor: LRA 22WVpower P I V I RtR Equivalent Resistance: tot121R11RR area A LPage 3 of 3 10/11/2009 M.Dubson PHYS1120 Notes ©University of Colorado at Boulder Things that are always true in circuits: elements in series always have the same current: elements in parallel always have the same voltage: voltage change along an unbroken ideal wire is zero (since we assume Rwire = 0 ) : wire wireV IR I 0 0 ideal battery means constant V for any current, current depends on the circuit K's Current Law (Junction Law) total current into junction = total current out of junction : 1 2 3I I I K's Voltage Law (Loop Law): total voltage change around any closed loop is zero Ammeters and Voltmeters To prepare for Exam 1: Review Concept Tests, CAPA problems, and Tutorial HW. (Read question and try to remember reasoning that gets to the answer) Prepare your formula sheet. Take the practice exam. It is no good to memorize answers. You have to understand and remember how you got the answers. R1 R2 I I R3 I I V Rbig Rsmall Ismall Ibig V same across both R's I2 I3 I1 I1 junction
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