Let four point charges qa, qb, qc, and qd placed on the vertices of a square on side a.

1. Find the electric field exerted on the qa charge.

2. Find the electrical potential exerted on the qa charge, deduce the potential energy of the qa charge

We give: a=2.8 10-10 m, qa = 1.6 10-19 C

We take qb= qc = -qa e and qd = 2qa root of 2