$A$ charge produces an electric field of $1\, N/C$ at a point distant $0.1\, m$ from it. The magnitude of the charge is:

Two charged thin infinite plane sheets of uniform surface charge density $\sigma_{+}$ and $\sigma_{-}$ where $\left|\sigma_{+}\right|>\left|\sigma_{-}\right|$ intersect at a right angle. Which of the following best represents the electric field lines for this system?

What will be the magnitude of the electric field at point $O$ as shown in the figure? Each side of the figure has length $l$ and segments are perpendicular to each other.

$(a)$ 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 electric field at the center of a semi-circle of radius $a$ and linear charge density $\lambda$ is given by:

Four point charges are placed at the vertices of a regular hexagon as shown in the figure below. What will be the net electric field at the centre?