For a circuit shown in Figure switch S1, is closed at t=0, then at t=(2R2+R1)C,S1 is opened and S2 is closed. a. Find the charge on capacitor at t=(2R2+2R1)C. b. Find current through R2 (adjacent to the battery) at t=(3R1+2R2)C.
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Solution
a. For t=0 to t=(2R2+R1)C, capacitor gets charged from all the three resistors. So q=CE[1−e1(2R2+R1)C]. Putting t=(2R2+R1)C, we get q1=CE[1−e−1]=CE(e−1)e. Now battery is disconnected and the capacitor gets discharged through R1 after S1 is opened and S2 is closed. So
∫q2q1dqq−(2R2+2R1)C∫(2R2+R1)CdtR1C or q2=q1e=CE(e−1)e2