Question

Q3: 20 In Figure-3, the switch was initially closed for a long time. Att = 0, it is opened. Calculate (i) ve(0+). (0+), ic(O+) and Ve(0) [4+4+2+2) (ii) vo(t) when 120 t=0 vacot) 9:375V 50 - 1 Rch tza - 52 switch 20 die-375 V/S (tot) = -1815A 25V 30 Vc + C=0.5F Lo 4:37e-046 v Figure-3

Answer 1

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Solution: - at to switch is opened. Calculate :- 1) Uclot), duc (ot), iclot) & Vc loo) dt ii) Velt) when to 512 5 so T to {22 { 32 25v ut GO.SE * at tro Copacitor is fully charged & ciruit is in steady state, so capacitor will be open circuited 330 250 320 to So Valo) res voltage across 3 resistor Velo) - 25x3, 75 - 9.375U 3+5 As voltage across capaitor cannot change suddenly, so UcCo-). Vel) = Uc (ot) Uclot) = 9.375 v * at to E 32

So here capacitor is charged at 9.375 Volts & it will discharge throyle (30#20 = 5m) Senator. Standard Discharging equation for RC circuit res Velt) = Vco e the Uco = writical capacitor coltage To fine constant - RC here co= 9.375U, R=52, C = O.SE Vects - 9.3750 t/2.5 Uc(t) = 9.375e-0.ut u dt * duct) -0.4x 9.375e-Out duelo"). -049-375e duc Cot) - - 3.75 Us dt dt * Welt) = C.dvelt? et iclot) - 0.5x-3.75 lclot) = -1975 A * Veloo) - et Velt) t700 = 9.375e Uc6= OV