Task 30869.

Point charge 3 nC, nC -1, -1 nC located on the plane in the lattice sites with the cell in the form of a square with side a = 0.1 m. Lattice sites, which are indicated charge given radius vectors r1 = (0,0), r2 = (a, 0), r3 = (0, a), r4 = (- a, -a). The remaining nodes are no charges. To determine the dipole moment of the system of charges and their potential energy U in an external electric field E = (- 100.0) / m.