Distinguish between electric potential and electric potential energy.

If $3$ charges of magnitude $q$ each are placed at the vertices of an equilateral triangle of side $l \ cm$,what is the net potential energy of the system?

What is the change in kinetic energy of an $\alpha$-particle when it moves from a point at $70\ V$ to a point at $50\ V$?

Three charges each of value $+q$ are placed at the corners of an isosceles triangle $ABC$ with sides $AB = AC = 2a$. The midpoints of $AB$ and $AC$ are $D$ and $E$ respectively. The work done in taking a charge $Q$ from $D$ to $E$ is (where $\varepsilon_0$ is the permittivity of free space):

There are four concentric shells $A, B, C$ and $D$ of radii $a, 2a, 3a$ and $4a$ respectively. Shells $B$ and $D$ are given charges $+q$ and $-q$ respectively. Shell $C$ is now earthed. The potential difference $V_A - V_C$ is:

Two point charges are located on the $x$-axis. $q_1 = -1 \ \mu C$ at $x = 0$ and $q_2 = +1 \ \mu C$ at $x = 1 \ m$. Find the work done in bringing a third charge $q_3 = +1 \ \mu C$ from infinity to $x = 2 \ m$.