154 Direct Current CircuitsP28.66Start at the point when the voltage has just reached 23∆Vand the switch has just closed. The voltage is 23∆Vand isdecaying towards 0 V with a time constant RC2∆∆VtVeCtRCaf=LNMOQP−232.We want to know when ∆Cwill reach 13∆V.Therefore,13232VVe=LNMOQP−ore−=212ortRC122=ln .VR1R2∆V+C∆VcVoltagecontrolledswitchFIG. P28.66After the switch opens, the voltage is 13∆V, increasing toward ∆Vwith time constant RRC+bg:∆VCtR RC=−LNMOQP−+23.WhenVC=232323∆Veore=12.SoRC2122=+lnandTt tR RC=+=+1222ln.P28.67(a)First determine the resistance of each light bulb: P=∆VR2RV===∆Ωaf af12060 0240VW..We obtain the equivalent resistance Reqof the network of lightbulbs by identifying series and parallel equivalent resistances:FIG. P28.67RReq+123111240120360
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .