Barron's 2nd Edition PT1 Q46

Barron's Book

46) This question asks us to find the electric potential at the origin. To do so, we can use this formula.

Where V is voltage, k is Coulomb's constant, q is charge and r is distance

We need to remember that electric potential is a scalar values, so we'll sum the potential produced by each charge. Our next step is to actually calculate the voltage produced by each charge at that point.

Where V is voltage, k is Coulomb's constant, q is charge, and r is distance

When calculating the electric potential of the left charge, although the charge is at -2 on the graph, we still use +2 because we are not concerned whether the charge is above, below, on the right, or any other direction around the point. All we care about is the distance from the charge to the point.

Answer: A