Three charges $2q, -q, -q$ are located at the vertices of an equilateral triangle. At the centre of the triangle:

Calculate the electric field at the origin due to an infinite number of charges as shown in the figure.

Five positive charges, each having charge $q$, are placed at the vertices of a regular pentagon as shown in the figure. The electric potential $(V)$ and the electric field $(\vec{E})$ at the center $O$ of the pentagon due to these five positive charges are:

The figures below show regular hexagons with charges at the vertices. In which of the following cases is the electric field at the centre not zero?

Two point charges $q_{A} = 3\; \mu C$ and $q_{B} = -3\; \mu C$ are located $20\; cm$ apart in vacuum.
$(a)$ What is the electric field at the midpoint $O$ of the line $AB$ joining the two charges?
$(b)$ If a negative test charge of magnitude $1.5 \times 10^{-9}\; C$ is placed at this point,what is the force experienced by the test charge?

$A$ uniformly charged rod of length $4\,cm$ and linear charge density $\lambda = 30\,\mu C/m$ is placed as shown in the figure. Calculate the $x-$ component of the electric field at point $P$.