Electric potential at any point is `V=-5x +3y+sqrt(15)z`, then the magnitude of the electric field is

Explanation

The four charges q each are placed at the corners of a square of side a. Find the potential energy of one of the charges

The electric potential of a point A due to charges B, C and D is
`V=(1)/(4pi epsilon_(0))q/a+1/(4pi epsilon_(0))q/(sqrt(2)a)+1/(4pi epsilon_(0))q/a=1/(4pi epsilon_(0))(2+1/sqrt(2))q/a`
`:.` Potential energy of the charge at A is `PE =qV=1/(4pi epsilon_(0))(2+1/sqrt(2))q^(2)/a`