If a charge $16Q$ is at point $A$ and a charge $25Q$ is at point $B$, then calculate $\left|\overrightarrow{E}\right|$ at origin.

The charge per unit length of the four quadrants of the ring are, $2\lambda$, $-2\lambda$, $\lambda$ and $-\lambda$, respectively. What is the electric field at the centre?

A charged ball $B$ hangs from a silk thread $S$, which makes an angle $\theta$ with a large charged conducting sheet $P$, as shown in the figure. The surface charge density $\sigma$ of the sheet is proportional to,

A thin semi-circular ring of radius $r$ has a positive charge $q$ distributed uniformly over it. The net field $\overrightarrow{E}$ at the centre $O$ is,