PHY2061 R. D. Field Department of Physics chp36_3.doc University of Florida RL Circuits "Building-Up" Phase: Connecting the switch to position Acorresponds to the "building up" phase of an RL circuit. Summing all the potential changes in going around the loop gives ε−−=IRLdIdt0, where I(t)is a function of time. If the switch is closed (position A) at t=0 and I(0)=0(assuming the current is zero at t=0) then d Id tIR= −−1τε, where I have define τ=L/R. Dividing by (I-ε/R) and multiplying by dt and integrating gives ()dIIRdtIt−= −∫∫ετ/001, which implies ln//IRRt−− = −εετ. Solving for I(t)gives ()I tRet( )/=−−ετ1. The potential change across the inductor is
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