A thin, uniformly charged ring of radius $R$ carries a total charge $Q$. A point charge $q$ is placed at the center of the ring. The force required to move the charge $q$ a small distance $z$ along the axis of the ring is proportional to:

$'n'$ charges $Q,\,4Q,\,9Q,\,16Q$ are placed at distance of 1,2,3 meter from point $'O'$ on the same straight line. The electric intensity at $'O'$ is

An infinite number of charges each of magnitude $'q'$ are placed on $x - axis$ at distances of 1,2,4,8 ….meter from the origin. The intensity of the electric field at origin is

Two charges $+ 5\mu C$ and $+ 10\mu C$ are placed $20\;cm$ apart. The net electric field at the mid-point between the two charges is

Infinite charges of magnitude q each are lying at $x = 1,2,4,8..$ metre on X-axis. The value of intensity of electric field at point $x = 0$ due to these charges will be

Charges $+ 2q, + q$ and $+ q$ are placed at the corners $A,B$ and $C$ of an equilateral triangle $ABC.$ If $E$ is the electric field at the circumcentre $O$ of the triangle, due to the charge $+ q,$ then the magnitude and direction of the resultant electric field at $O$ is

Equal charges $q$ are placed at the vertices $A\;{\rm{and\;}}B$ of an equilateral triangle $ABC$ of side $a.$ The magnitude of electric field at the point $C$ is

Two point charges +q and -q are separated by a distance d. What is the electric field at the midpoint between them?

A ring of radius $r$ carries a charge $Q$ uniformly distributed over its length. A charge $q$ is placed at its centre will experience a force equal to

$'n'$ charges $Q,\,4Q,\,9Q,\,16Q$ are placed at distance of 1,2,3 meter from point $'O'$ on the same straight line. The electric intensity at $'O'$ is

Two point charges $\left( { + Q} \right)$ and $\left( { - 2Q} \right)$ are fixed on the $X$-axis at positions $a$ and $2a$ from origin respectively. At what positions on the axis, the resultant electric field is zero