Exercise E7 Charges on a Ballon
A balloon has a charge of $Q=7~{\rm nC}$ on its surface.
How many additional electrons are on the balloon?
\begin{align*}
Q &= 7~{\rm nC} = 7\cdot 10^{-9}~{\rm C} \\
n_{\rm e} &= {{7*10^{-9}~{\rm C}}\over{1.6022*10^{-19}~{\rm C/electron}}}
= 43.7*10^{9}~{\rm electrons}
\end{align*}
\begin{align*}
43.7*10^{9}~{\rm electrons}
\end{align*}