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 ........ $N / C$.

Two point charges $+10 q$ and $-4 q$ are located at $x=0$ and $x=L$ respectively. What is the location of a point on the $x$-axis from the origin, where the net electric field due to these two point charges is zero? $(r = \text{required distance})$

$(a)$ Consider an arbitrary electrostatic field configuration. $A$ small test charge is placed at a null point (i.e.,where $E = 0$) of the configuration. Show that the equilibrium of the test charge is necessarily unstable.
$(b)$ Verify this result for the simple configuration of two charges of the same magnitude and sign placed a certain distance apart.

The dimensional formula of electric field is . . . . . . .

The energy density of an electric field is proportional to which of the following?

Two point charges $-10 \mu C$ and $+5 \mu C$ are situated on the $X$-axis at $x=0$ and $x=\sqrt{2} \ m$. The point along the $X$-axis where the electric field becomes zero is: