Page 1 of 3 PHYS1120 Exam III review Things to remember for PHYS1110: algebra, trig (sin, cos, ..) vector math, especially vector addition, Fnet = ma problems, free-body diagrams Exam1 and Exam2 Material : E-fields, Gauss's Law, voltage, capacitors, circuits. Last part of Chapter 26 : RC circuits • Voltage across a capacitor is always CqVC=. • An uncharged capacitor has ∆V= 0 , acts like a wire, as short (does not resist the flow of current). • A fully charged capacitor has I = 0, acts like an open switch. • time constant is τ = RC Ch. 27 Magnetic fields • • This is the definition of B . on qFqv=×GKKBF • When both E-field and B-field are present: Ntot E BqEFF=+GGGG • Motion of charge in magnetic field and in velocity selector. • on wireFIL=×BGKK, force and torque on a current loop Ch. 28 Sources of Magnetic fields • Currents cause magnetic fields (B-fields) • Biot-Savart Law: 02ˆIdrdB4rµπ×=KKA (Know what all the symbols mean) 10/11/2009 M.Dubson PHYS1120 Notes ©University of Colorado at BoulderPage 2 of 3 • Ampere's Law: 0enclosedBd Iµ⋅ =∫KKAvL B Be able to use Ampere to derive B-field outside long straight wire: 0IB2rµ=π , I B-field inside long wire: 02IrB2Rµ=π B-field inside solenoid: 0Bn=µ IB=+GGG (No need to memorize these formulas; know how to derive them) • "modified right-hand rule" point thumb in direction of straight thing, fingers curl in sense of circular thing. • B-field is a vector: BB tot 1 2 • parallel currents attract; anti-parallel currents repel • Gauss's Law for B-fields: Bda 0⋅ =∫KKv ⇒ Magnetic monopoles do not exist. • field of a solenoid, permanent magnet acts like solenoid Ch. 29 Faraday's Law • Faraday's Law: An emf (= battery voltage) is caused by a changing magnetic flux: (N loops)dNdtΦ= −E ( where Φ is the flux through 1 loop) magnetic flux Φ, emf around a loop B da= ⋅∫KKEd= ⋅∫KKAvLE Be able to use Faraday's Law to derive E-field inside or outside a solenoid. net atomic current on rimuniform B(out) Side View: atomic current on rim, like solenoid End View: N S B-field enters B-field comes out of "North" end "South" end 10/11/2009 M.Dubson PHYS1120 Notes ©University of Colorado at BoulderPage 3 of 3 • Lenz's Law: Iinduced creates Binduced in direction that opposes the change in flux. • Motors and generators • Eddy current forces always oppose the motion To prepare for any exam: • Study my online lecture Notes. • Review Concept Tests, CAPA problems, and Tutorial HW. (Read question and try to remember reasoning that gets to the answer) • Prepare your formula sheet. Prioritize: which are the important equations? • 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
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