Fill in the blanks
Potential energy `upsilon` of a charge q at poistion vector `vector r` in an external field is________.

What is the potential energy of a charge q in a given filed?

Give the expression for potential energy of a system of two charges q_1 and q_2 in an external field.

Consider a dipole with charges +q and -q. Find out the expression of potential energy of the dipole for an external field E.

Fill in the blanks The dipole moment vector P of an electric dipole is defined by P = ______

The volume charge density within a volume is rho(r ) . What is the force on a small test charge q_0 placed outside the volume having position vector vector r_0 with respect to the same origin considered to specify the position vector of the charge distribution within the volume.

Fill in the blanks: The potential differences between the fixed layer and the diffused layer of opposite charges of a double layer is called the___________.