Why does a configuration of charges possess potential energy?

What is potential energy?

Obtain an expression for potential energy of the configuration of three charges Hence generalise the result for a system of n point charges?

Why CB configuration is seldom used?

What does the negative sign in the expression for potential energy ( U = -p E cos theta) signify?

Consider an arbitrary electrostatic field configuration. A small test charge is placed at a null point (i.e., where E = 0) of the configuration. Show that the equilibrium of the test charge is necessarily unstable. Verify this result for the simple configuration of two charges of the same magnitude and sign placed a certain distance apart.