On the lower left corner of a square is a fixed charge qLL = 1.5x10^-9 C and on the loser right corner is a fixed charge qLR = 4.0x10^-9 C. The square has a side length L = 0.25 meters.

Question

a) Find the electric potential energy of a third charge q = -6x10^-9 C placed at the upper left corner of this square.

b) Find the potential energy of this same third charge q placed at the upper right corner of the square.

Answer 1

Easy. Potential is a scalar, so add the voltage from each of the other charges.

Upper left Potential

V=kqLL/sidelength + kQLR/diagonal length

Then the electric potentialenergy of the third charge is

V*q

Do the same technique for the last charge, add the voltage potential from the three charges, then for elec potential energy, that sum times qur.