In steady state heat conduction, the equations that determine the heat current $j ( r )$ [heat flowing per unit time per unit area] and temperature $T( r )$ in space are exactly the same as those governing the electric field $E ( r )$ and electrostatic potential $V( r )$ with the equivalence given in the table below.

Heat flow	Electrostatics
$T( r )$	$V( r )$
$j ( r )$	$E ( r )$

We exploit this equivalence to predict the rate $Q$ of total heat flowing by conduction from the surfaces of spheres of varying radii, all maintained at the same temperature. If $\dot{Q} \propto R^{n}$, where $R$ is the radius, then the value of $n$ is

Four charges are placed at the circumference of a dial clock as shown in figure. If the clock has only hour hand, then the resultant force on a charge $q_0$ placed at the centre, points in the direction which shows the time as

Two point charges $+q$ and $-q$ are held fixed at $(-d, 0)$ and $(+d, 0)$ respectively of a $(x, y)$ coordinate system. Then

If the distance between the plates of a capacitor having capacity $C$ and charge $Q$ is doubled then work done will be

 An insulator plate is passed between the plates of a capacitor. The the displacement current

Two condensers $C_1$ and $C_2$ in a circuit are joined as shown in figure. The  potential of point $A$ is $V_1$ and that of $B$ is $V_2$. The potential of point $D$ will be