In Millikan's experiment, an oil drop having charge $q$ gets stationary on applying a potential difference $V$ in between two plates separated by a distance $d$. The weight of the drop is
$\frac{q}{{Vd}}$
$q\frac{d}{V}$
$q\,Vd$
$q\frac{V}{d}$
Three identical small electric dipoles are arranged parallel to each other at equal separation a as shown in the figure. Their total interaction energy is $U$. Now one of the end dipole is gradually reversed, how much work is done by the electric forces.
Three charges are placed along $x$-axis at $x=-a, x=0$ and $x=a$ as shown in the figure. The potential energy of the system is
An electron enters in high potential region ${V_2}$ from lower potential region ${V_1}$ then its velocity
On rotating a point charge having a charge $q$ around a charge $Q$ in a circle of radius $r$. The work done will be