Uniform electric field of magnitude 100 V/m in space is directed along the line y = 3 + x. Find the potential difference between point (3, 1) & (1, 3)

Slope electric field lines m1 = 1 and slope of the line joining points (3,1) and (1,3) is m2=3-11-3 =-1.Since m1×m2 =-1 ,the line joining the points must be an equipotential surface .