Physics - Capacitor Question with Solution | TestHub

With S at 1, the $2\mu F$ is in parallel with the right $1\mu F$: a $3\mu F$ bank in series with the left $1\mu F$ across 20 V, giving charge $Q=15\mu C$.

With S at 2 the circuit is the mirror image, so the total stored energy is unchanged; the battery pushes $\Delta Q=10\mu C$ around during the changeover.

Heat liberated $=W_{\text{battery}}=20\times 10\mu C=2\times 10^{-4}$ J, so n = 2.