In moving from $A$ to $B$ along an electric field line, the electric field does $6.4 \times {10^{ – 19}}\,J$ of work on an electron. If ${\phi _1},\;{\phi _2}$ are equipotential surfaces, then the potential difference $({V_C} – {V_A})$ is…..$V$

A circle of radius $R$ is drawn with charge $+ q$ at the centre. A charge $q_0$ is brought from point $B$ to $C$, then work done is

Two equal charges $q$ are placed at a distance of $2a$ and a third charge $ – 2q$ is placed at the midpoint. The potential energy of the system is

A block of mass $m$ moving with speed $v$ compresses a spring through distance $x$ before its speed is halved. What is the value of spring constant ?

If $50$ joule of work must be done to move an electric charge of $2 \,C$ from a point, where potential is $-10$ volt to another point, where potential is $V$ volt, the value of $V$ is ……… $V$