\begin{problem*}{25.21}
-Two particles each with charge $+2.00\U{$\mu$C}$ are lopcated on the
+Two particles each with charge $+2.00\U{$\mu$C}$ are located on the
$x$ axis. One is at $x=1.00\U{m}$, and the other is at
$x=-1.00\U{m}$. \Part{a} Determine the electric potential on the $y$
axis at $y=0.500\U{m}$. \Part{b} Calculate the change in electric
potential energy of the system as a third charged particle of
-$-3.00\U{$\mu$C}$ is brought in from infinitely far away to a positino
+$-3.00\U{$\mu$C}$ is brought in from infinitely far away to a position
on the $y$ axis at $y=0.500\U{m}$.
\end{problem*}