Three identical parallel plate capacitors are connected in parallel to a 2 volt battery. The battery is disconnected and the three capacitors are joined in series. What is the potential difference between X and Y?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 6 V
Capacitors in parallel all have the potential difference of the battery. When they are disconnected from the battery and then rejoined in series, the charge on each capacitor does not change, because the joined plates carry equal and opposite charges and nothing is added or removed. A capacitor with unchanged charge and unchanged capacitance keeps the same potential difference, and in series the potential differences add.
\( q = CV = C\times2\,\mathrm{V} \) on each capacitor
\( \displaystyle V_{\mathrm{each}} = \frac{q}{C} = 2\,\mathrm{V} \)
\( V_{XY} = 2 + 2 + 2 = 6\,\mathrm{V} \)