# The switch has been open for a long time then at t 0

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Unformatted text preview: uniformly throughout its volume, the magnitude of the potential difference |Vb – V0| would 53% A. increase B. decrease ALWAYS START FROM DEFINITION OF POTENTIAL b ∆ V = − ∫ E ⋅ dr 0 C. stay the same Break integral into two pieces a b ∆V = − ∫ E ⋅ dr − ∫ E ⋅ dr 0 conductor: = 0 insulator: 0 a same for conductor & insulator Physics 212 Lecture 29, Slide 9 RL Circuits 1 In the circuit below, V = 6 Volts, R = 10 Ohms, L = 100 mH. The switch has been open for a long time. Then, at t = 0, the switch is closed. What is the time constant for the current through the inductor? 30% A. R/L B. R/2L C. L/R D. 2L/R E. L/2R I 2 I – I1 L L dI1 − ( I − I1 ) R = 0 dt IR = V − L 1 I1 2 L dI1 + IR − V = 0 dt dI1 dt dI1 dI − V + L 1 + I1R = 0 dt dt 2L dI1 + I1R = V dt Strategy: Back to First Principles • The time constant is determined from a differential equation for the current through the inductor. • Equation for current through inductor obtained from Kirchhoff’s Rules τ= " L" 2 L = " R" R Physics 212 Lecture 29, Slide 10 Faraday’s Law A rectangular wire loop travels to the right with constant velocity, starting in a region of no magnetic field, moving into a region with a constant field pointing into the page (shaded rectangle below), and continuing into a region of no magnetic field. Which plot below best represents the induced current in the loop (Iloop) as it travels from the left through these three regions? Note: a positive Iloop corresponds to a counter-clockwise current. Current in...
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