$A$ charge of $3 \ C$ experiences a force of $3000 \ N$ when placed in a uniform electric field. The potential difference between two points separated by a distance of $1 \ cm$ along the field lines is.....$V$

$A$ semicircular ring of radius $0.5 \ m$ is uniformly charged with a total charge of $1.4 \times 10^{-9} \ C$. The electric field intensity at the center of the ring is ........ $V/m$.

$A$ metallic ring is uniformly charged as shown in the figure. $AC$ and $BD$ are two mutually perpendicular diameters. The magnitude of the electric field at $O$ due to arc $AB$ is $E$. What would be the magnitude of the electric field at $O$ due to arc $ABC$?

$A$ thin glass rod is bent in a semicircle of radius $R$. $A$ charge is non-uniformly distributed along the rod with a linear charge density $\lambda = \lambda_0 \sin \theta$ (where $\lambda_0$ is a positive constant and $\theta$ is the angle with the $x$-axis). The electric field at the centre $P$ of the semicircle is,

$A$ positive charge $q$ is placed in a spherical cavity made in a positively charged sphere. The centres of the sphere and the cavity are displaced by a small distance $\vec{l}$. The force on charge $q$ is:

$A$ unit negative charge with mass $M$ resides at the mid-point of the straight line of length $2a$ connecting two fixed charges of magnitude $+Q$ each. If it is given a very small displacement $x$ $(x \ll a)$ in a direction perpendicular to the straight line, it will: