The electric potential at the centre of two concentric half rings of radii $R_1$ and $R_2$,having same linear charge density $\lambda$ is

Four electric charges $+q, +q, -q$ and $-q$ are placed in order at the corners of a square of side $2r$. The electric potential at a point $P$ midway between the two negative charges is:

$A$ and $C$ are concentric conducting spherical shells of radius $a$ and $c$ respectively. $A$ is surrounded by a concentric dielectric of inner radius $a$,outer radius $b$ and dielectric constant $k$. If sphere $A$ is given a charge $Q$,the potential at the outer surface of the dielectric (at radius $b$) is:

$A$ positively charged ring is in the $y-z$ plane with its centre at the origin. $A$ positive test charge $q_0$,held at the origin,is released along the $x$-axis. Then its speed

Three equal charges are placed at the corners of an equilateral triangle. Which of the graphs below correctly depicts the equally-spaced equipotential surfaces in the plane of the triangle? (All graphs have the same scale.)

The electric potential energy of a $2 \mu C$ charge is $3 \times 10^{-5} \text{ J}$ at a point in a uniform electric field. The electric potential at the point is . . . . . . $V$.