Four charges equal to $-Q$ are placed at the four corners of a square and a charge $q$ is at its centre. If the system is in equilibrium, the value of $q$ is
$-\frac{Q}{4} (1 + 2 \sqrt 2 )$
$\frac{Q}{4} (1 + 2 \sqrt 2 )$
$-\frac{Q}{2} (1 + 2 \sqrt 2 )$
$\frac{Q}{2} (1 + 2 \sqrt 2 )$
Calculate the work done in taking a charge $-2 \times 10^{-9} \,C$ from $A$ to $B$ via $C$ is ......... (in diagram)
Two identical small spheres carry charge of $Q_1$ and $Q_2$ with $Q_1>>Q_2.$ The charges are $d$ distance apart. The force they exert on one another is $F_1.$ The spheres are made to touch one another and then separated to distance $d$ apart. The force they exert on one another now is $F_2.$ Then $F_1/F_2$ is
A dipole having dipole moment $p$ is placed in front of a solid uncharged conducting sphere are shown in the diagram. The net potential at point $A$ lying on the surface of the sphere is :-
Half of the space between parallel plate capacitor is filled with a medium of dielectric constant $K$ parallel to the plates . If initially the capacity is $C$, then the new capacity will be
If the distance between the plates of a capacitor having capacity $C$ and charge $Q$ is doubled then work done will be