The equivalent capacitance of the following arrangement is:
               
1. \(18~\mu \text{F}\)
2. \(9~\mu \text{F}\)
3. \(6~\mu \text{F}\)
4. \(12~\mu \text{F}\)

Two capacitors of capacitance \(6~\mu\text{F}\) and \(3~\mu\text{F}\) are connected in series with battery of \(30~\text{V}\). The charge on \(3~\mu\text{F}\) capacitor is:
          
1. \( 3 ~\mu\text{C}\)
2. \( 1.5 ~\mu\text{C}\)
3. \( 60~\mu\text{C}\)
4. \( 900~\mu\text{C}\)

Three charges \(-Q,q,\) and \(-2Q\) are placed along a line as shown in the figure. The system of charges will have a positive potential energy configuration when \(q\) is placed at the midpoint of line joining \(-Q\) and \(-2Q\) if:

Work done to carry a negatively charged body in direction of the electric field:
(assuming no other force is acting on the body)

Two concentric metallic spherical shells \(A\) and \(B\) of radii \(a\) and \(b\) respectively \((b>a)\) are arranged such that outer shell is earthed and inner shell is charged to \(Q\). Charge on the outer surface of outer shell will be:
1. \(- \frac{Q a}{b}\)
2. \(Q \left[1 - \frac{a}{b}\right]\)
3. \(-Q\)
4. zero

The equivalent capacitance across \(A\) and \(B\) in the given figure is:

Surface charge density on the positive plate of a charged parallel plate capacitor is \(\sigma.\) Energy density in the electric field of the capacitor is:
1. \(\dfrac{\sigma^2}{\varepsilon_0}\)
2. \(\dfrac{\sigma^2}{2\varepsilon_0}\)
3. \(\dfrac{\sigma}{\varepsilon_0}\)
4. \(2\sigma^2 \varepsilon_0\)

Two capacitors of capacity \(2~\mu\text{F}\) and \(3~\mu\text{F}\) are charged to the same potential difference of \(6~\text V.\) Now they are connected with opposite polarity as shown. After closing switches \(S_1~\text{and}~S_2\), their final potential difference becomes: