As the capacitors 4 and 2 are connected in parallel and are in series with 6 capacitor, their equivalent capacitance is

Charge in the circuit


Since, the capacitors and 2 are connected in parallel, therefore potential difference across them is same.

Also
or

Since, are parallel to their equivalent capacitance will be . Now, are in series, so the net equivalent capacitances of circuit.



Since, is the voltage of the battery, so charge on this system


If the capacitor breaks down then total equivalent capacitance

New charge stored


Change in total charge

Since, the proton is moving against the direction of electric field so, work is done by the proton against electric field. It implies that electric field does negative work on the proton.
Again, proton is moving in electric field from low potential region to high potential region hence, its potential energy increases.

When charge is at , then its potential energy is

Where charge is at , then

Hence, change in potential energy

applying the condition of rotational equilibrium

The two capacitor the circuit are in parallel order, hence

The work done in charging the equivalent capacitor is stored in the form of potential energy.
Hence,

Applying the condition of rotational equilibrium,

But

applying principle of moments
F (0.6)=100(0.8)
ÞF=133.3N

Potential difference between two equipotential surfaces A and B.



Or

Or
Similarly,
Since,
therefore