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Electric circuits miscellaneous

  1. The switch SW shown in the circuit is kept at position ‘1’ for a long duration. At t = 0+, the switch is moved to position ‘2’. Assuming | Vo2 | > | Vo1 |, the voltage vc (t) across the capacitor is

    1. Vc(t) = -Vo2(1 - e-t / 2RC - Vo1
    2. Vc(t) = Vo2(1 - e-t / 2RC + Vo1
    3. Vc(t) = -(Vo2 + Vo1) (1 - e-t / 2RC - Vo1
    4. Vc(t) = (Vo2 - Vo1) (1 - e-t / 2RC + Vo1
Correct Option: D

When the switch SW is at position 1, the capacitor C is charged to voltage V01.
Now, when the switch SW is thrown to position 2, the circuit becomes as shown below :

VC (0-) = VC (0+) = V01
Using KVL in the circuit, we get

V02 - 2R
dq
-
q
= 0
dtc

dq
=
dt
cV02 - q2RC




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