On moving a charge of $20 \; C$ by $2 \; cm$,$2 \; J$ of work is done. The potential difference between the points is (in $V$):

The work done to take an electron from rest where potential is $-60\, V$ to another point where potential is $-20\, V$ is given by.....$eV$.

$A$ uniformly charged ring of radius $3a$ and total charge $q$ is placed in the $xy$-plane centered at the origin. $A$ point charge $q$ is moving towards the ring along the $z$-axis and has speed $v$ at $z = 4a$. The minimum value of $v$ such that it crosses the origin is

Two charges $8 \ \mu C$ each are placed at the corners $A$ and $B$ of an equilateral triangle of side $0.2 \ m$ in air. The electric potential at the third corner $C$ is

The ratio of electric potentials at the point $E$ to that at the point $F$ is

$A$ sphere of radius $1\,cm$ has a potential of $8000\,V$. The energy density near its surface will be: