Question

C1=10 uf c2=40 uf c3=20uf c4=30 uf find the capacitance between the point A and B when 1) the key K is closed 2) the key is open

Answer 1

two capacitors C1 = 2uF and C2 = 4uF are connected in series so, equivalent capacitance is Ceq = C1.C2/(C1 + C2) = 2 × 4/(2 + 4) = 4/3 uF

we know,

Q = CV

where Q is charge , C is the capacitance of capacitor and V is the potential difference.

now, Qnet in circuit = equivalent capacitance of capacitors attached in circuit × potential difference

Qnet = 1200 × 4/3 = 1600uC

both the capacitors are in series so, charge passing through both are same. e.g., Q = 1600uC

hence, Q = CV

here, C = 2uF , Q = 1600 uC

now, V = 1600uC/2uF = 800v

hence, potential difference across 2uF is 800v