1 \begin{problem*}{25.21}
2 Two particles each with charge $+2.00\U{$\mu$C}$ are located on the
3 $x$ axis. One is at $x=1.00\U{m}$, and the other is at
4 $x=-1.00\U{m}$. \Part{a} Determine the electric potential on the $y$
5 axis at $y=0.500\U{m}$. \Part{b} Calculate the change in electric
6 potential energy of the system as a third charged particle of
7 $-3.00\U{$\mu$C}$ is brought in from infinitely far away to a position
8 on the $y$ axis at $y=0.500\U{m}$.
14 V_3 = k_e \frac{q_1}{r_{13}} + k_e \frac{q_2}{r_{12}}
15 = 2 k_e \frac{2\U{$\mu$C}}{\sqrt{(1.00\U{m})^2 + (0.500\U{m})^2}}
21 \Delta U = q_3 V_3 - q_3 V_\infty = q_3 V_3 = \ans{-96.5\U{mJ}}