Find Ctot and time for 3 volts 2 Switsh a Find CTor Ci0pts b

2) Switsh a) Find CTor, Ci0pts.) b)Aftr the switch is closed, hew lon will it be until there are 3 Vo Its hesuiteh is clased hou lon a cross the 90 capacrte (20 pts (xorts,)

Solution

a) 30 and 60 uF are in parallel,

so equivalent of these two,

C\' = 30 + 60 uF = 90 uF

C\' and 90 uF are in series,

1/Ceq = 1/90 + 1/90

Ceq = 45 uF

b) charge will be same same on both similar as in Ceq.

so, Q = Q0 ( 1 - e^- ( t /RC))

CV = C V0 ( 1 - e^- ( t /RC))

3 = 12 ( 1 - e^-(t / (120 x 45 x 10^-6)))

t = 1.55 x 10^-3 s = 1.55 ms