Two conducting spheres of radii $r_1$ and $r_2$ are charged to the same surface charge density. The ratio of electric fields near their surfaces is

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

Electrical as well as gravitational effects can be thought to be caused by fields. Which of the following is true for an electrical or gravitational field?

$A$ thin conducting ring of radius $R$ is given a charge $+Q.$ The electric field at the centre $O$ of the ring due to the charge on the part $AKB$ of the ring is $E.$ The electric field at the centre due to the charge on the part $ACDB$ of the ring is

There exists an electric field of magnitude $E$ in the $x$-direction. If the work done in moving a charge of $0.2 \, C$ through a distance of $2 \, m$ along a line making an angle $60^{\circ}$ with the $x$-axis is $4 \, J$,then the value of $E$ is ........ $N / C$.

Four charges $+q, +2q, +q$ and $-2q$ are placed at the corners $A, B, C$ and $D$ of a square respectively. The force on a unit positive charge kept at the centre $O$ is