A capacitor of capacitance \(C=900~\text{pF}\) is charged fully by \(100~\text{V}\) battery \(B\) as shown in Figure \((a)\). Then it is disconnected from the battery and connected to another uncharged capacitor of capacitance \(C=900~\text{pF}\) as shown in Figure \((b)\). The electrostatic energy stored by the system \((b)\) is:
       

1.	\(1.5\times 10^{-6}~\text{J}\)	2.	\(4.5\times 10^{-6}~\text{J}\)
3.	\(3.25\times 10^{-6}~\text{J}\)	4.	\(2.25\times 10^{-6}~\text{J}\)

A hollow metal sphere of radius \(R\) is given \(+Q\) charges to its outer surface. The electric potential at a distance \(\frac{R}{3}\) from the centre of the sphere will be:
1. \(\frac{1}{4\pi \varepsilon_0}\frac{Q}{9R}\)
2. \(\frac{3}{4\pi \varepsilon_0}\frac{Q}{R}\)
3. \(\frac{1}{4\pi \varepsilon_0}\frac{Q}{3R}\)
4. \(\frac{1}{4\pi \varepsilon_0}\frac{Q}{R}\)

Three capacitors, each of capacitance \(0.3~\mu \text{F}\) are connected in parallel. This combination is connected with another capacitor of capacitance \(0.1~\mu \text{F}\) in series. Then the equivalent capacitance of the combination is:

When a particle with charge \(+q\) is thrown with an initial velocity \(v\) towards another stationary change \(+Q,\) it is repelled back after reaching the nearest distance \(r\) from \(+Q.\) The closest distance that it can reach if it is thrown with an initial velocity \(2v,\) is: