If an electron moves from rest from a point at which potential is $50\, V$ to another point at which potential is $70\, V$,then its kinetic energy in the final state will be:

Which of the following is a volt?

$A$ pellet carrying a charge of $0.5 \, C$ is accelerated through a potential difference of $2000 \, V$. The kinetic energy attained by the pellet is:

Eight small drops,each of radius $r$ and having same charge $q$,are combined to form a big drop. The ratio between the potentials of the bigger drop and the smaller drop is

Charge is uniformly distributed on the surface of a hollow hemisphere. Let $O$ and $A$ be two points on the base of the hemisphere,where $O$ is the center of the base and $A$ is a point between the center and the rim. Let $V_O$ and $V_A$ be the electric potentials at $O$ and $A$ respectively. Then,

$A$ point charge $q$ of mass $m$ is placed at the center of a ring of radius $R$ carrying a charge $Q$. When it is slightly displaced,the point charge accelerates to infinity along the $x$-axis. The ultimate speed of the point charge is .......