Question

For the circuit shown, which of the following statements is true

• A. With S₁ closed, V₁ = 15 V, V₂ = 20 V
• B. With S₃ closed, V₁ = V₂ = 25 V
• C. With S₁ and S₂ closed V₁ = V₂ = 0
• D. With S₁ and S_­3 closed V₁ = 30 V, V₂ = 20 V

Answer 1

Answer: (D)

With S₁ and S_­3 closed V₁ = 30 V, V₂ = 20 V

Answer 2

When S₃ is closed, due to attraction with opposite charge, no flow of charge takes place through S₃. Therefore, potential difference across capacitor plates remains unchanged or V₁ = 30 V and V₂ = 20 V.

Alternate Solution

Charges on the capacitors are

– $q _ { 1 } = ( 30 ) ( 2 ) = 60 p C$, $q _ { 2 } = ( 20 ) ( 3 ) = 60 p C$

or $q _ { 1 } = q _ { 2 } = q ($ say $)$

The situation is similar as the two capacitors in series are first charged with a battery of emf 50 V and then disconnected.

When S₃ is closed, V₁ = 30 V and V₂ = 20 V.