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Unformatted text preview: Physics 7B WS C2 (rev. 2.0) Page 1 C-2. LR Circuits Questions for discussion 1 . Why does the current vary with time in an LR circuit 1 ? 2 . For the simplest type of LR circuit (consisting only of a battery ε , a resistance R, and an inductance L), the time constant is τ = L/R. What is the significance of this time constant? In other words, what does the time constant for an LR circuit tell you? 3. Consider again the simple type of LC circuit discussed in question 2. a) The inductor initially has no current flowing through it, and a switch closes and completes the circuit at time t=0. What, if any, is the inductor’s effect on the circuit at the instant the switch is thrown? That is, does it act like a battery, an open switch, or a closed switch? b) After a very long time (a few time constants, in practice), what, if any, is the inductor’s effect on the circuit? That is, does it act like a battery, an open switch, or a closed switch? 1 Some problems in LR circuits require solutions to differential equations. For the results you will need, and derivations of those results, see “Differential Equations for Circuit Problems” in the Supplementary Material at the end of the workbook, in the section “RC and LR Equations.”the end of the workbook, in the section “RC and LR Equations....
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