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Page 1 of 3 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: D V є D Uof q q f = - v v т E Чdr , D U of q = q D V i r r dV D V = E D x ( if E = constant and E P D x ) , E x = dx E hi V lo V Voltage is electrical height, E-field is slope v r if D r ^ E , D V = 0 , equipotential lines Voltage due to a point charge Q: V(r) = Voltage due to many charges: V(r) = е i kQ r Vi = е i k Qi = ri т k dq r Work done by external agent to move charge q through a voltage differenceV = Wext = D U of q = q D V . If charge q falls through a voltage differenceV, D KE = D PE = q D V Units of electron volts (eV). Ch.24 Capacitors +Q V = V E d –Q Q capacitance C V 10/11/2009 M.Dubson PHYS1120 Notes ©University of Colorado at Boulder Page 2 of 3 C depends only on size and shape: C o A d area A d Adding capacitors in series and parallel. stored energy = U energy per volume = u 1 1 1 Q2 Q V C V2 2 2 2 C U 1 o E 2 . volume 2 Ch.25, 26 Current and Circuits I = dQ , dt J = I = n q vd A (where n = #carriers/volume, vd = drift speed) 1 E , = resistivity = measure of internal friction, depends on composition r I Ohm's Law: V I R (where R = constant) lo V hi V J = sE = R V Resistance of a resistor: R = power P = r L A area A L DW V2 = I V = I2 R = Dt R Equivalent Resistance: R1 in series: R2 Rtot = R1 + R2 = R1 R tot = in parallel: R2 10/11/2009 M.Dubson PHYS1120 Notes = 1 1 1 + R1 R2 ©University of Colorado at Boulder Page 3 of 3 Things that are always true in circuits: elements in series always have the same current: I I I I Rbig R1 R2 V R3 Ismall Rsmall elements in parallel always have the same voltage: Ibig V same across both R's voltage change along an unbroken ideal wire is zero (since we assume Rwire = 0 ) : Vwire I R wire 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 I2 I1 I1 junction : I1 = I2 + I3 junction I3 junction 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. 10/11/2009 M.Dubson PHYS1120 Notes ©University of Colorado at Boulder