A parallel plate capacitor with air between the plates has a capacitance of $9\ pF$. The separation between its plates is '$d$'. The space between the plates is now filled with two dielectrics. One of the dielectric has dielectric constant $K_1 = 6$ and thickness $\frac{d}{3}$ while the other one has dielectric constant $K_2 = 12$ and thickness $\frac{2d}{3}$. Capacitance of the capacitor is now........$pF$

Three charges $4q,\,Q$ and $q$ are in a straight line in the position of $0$, $l/2$ and $l$ respectively. The resultant force on $q$ will be zero, if $Q = $

Figures below show regular hexagons, with charges at the vertices, In which of the following cases the electric field at the centre is not zero.

Calculate the work done in taking a charge $-2 \times 10^{-9} \,C$ from $A$ to $B$ via $C$ is ......... (in diagram)

A parallel plate condenser with plate area $A$ and separation $d$ is filled with two dielectric materials as shown in the figure. The dielectric constants are $K_1$ and $K_2$ respectively. The capacitance will be

If the electric potential of the inner shell is $10\,V$ and that of the outer shell is $5\,V$ , then the potential at the centre will be.....$V$