Dear student,
Length of the side of a cube = b
Charge at each of its vertices = q
A cube of side b is shown in the following figure.
d = Diagonal of one of the six faces of the cube
l = Length of the diagonal of the cube
The electric potential (V) at the center of the cube is due to the presence of eight charges at the vertices.
Therefore, the potential at the center of the cube is.
Regards