1 \begin{problem*}{20.47}
2 \Part{a} A $C = 3.00\U{$\mu$F}$ capacitor is connected to a $\Delta
3 V_a = 12.0\U{V}$ battery. How much energy $U_a$ is stored in the
5 \Part{b} If the capacitor had been connected to a $\Delta V_b =
6 6.00\U{V}$ battery, how much energy would have been stored?
7 \end{problem*} % problem 20.47
10 Simply plugging into the formula for energy stored in a capacitor we have
12 U_a &= \frac{1}{2} C (\Delta V)^2
13 = \frac{1}{2} (3.00\E{-6}\U{F}) \cdot (12.0\U{V})^2
14 = \ans{ 216 \U{$\mu$J}} \\
15 U_b &= \frac{1}{2} (3.00\E{-6}\U{F}) \cdot (6.0\U{V})^2
16 = \ans{ 54 \U{$\mu$J}}