Correct Answer - Option 4 : 350 V
CONCEPT
Capacitance: The capacitance tells that for a given voltage how much charge the device can store.
Q = CV
where Q is the charge in the capacitor V is the voltage across the capacitor and C is the capacitance of it.
In the Parallel circuit, the equivalent capacitance is the algebraic sum of all the capacitance.
In the Series circuit, the reciprocal of the equivalent capacitance is the algebraic sum of all the reciprocal of the capacitance.
Ceq = C1 + C2 + C3 +...... (In parallel)
1/Ceq = 1/C1 + 1/C2 + 1/C3 +...... (in series)
Calculations:
C1 = 15 μA, C2 = 5 μA, V1 = 400 V, V2 = 200 V
q1 = C1 × V1
= 15 × 10-6 × 400 = 6 mC
q2 = C2 × V2
= 5 × 10-6 × 200
= 1 mC
qeq = q1 + q2 = 7 mC
Ceq = C1 + C2 = 15 + 5 = 20 μ F
qeq = Ceq Veq
7 × 10-3 = 20 × 10-6 × Veq
Veq = 350 V