AP Physics C: Electricity and Magnetism / Unit 9: Electric Potential
9.1 Electric Potential Energy
Notes
$$U=\frac{kq_1q_2}{r},\qquad \Delta U=-\int\vec F\cdot d\vec r$$
- For a group of charges, add $U$ for every pair.
Practice
The work needed to bring two $+1$ μC charges from far apart to 0.1 m apart ($k=9\times10^9$):
$\displaystyle \frac{9\times10^9\cdot10^{-12}}{0.1}$.
Three charges: how many pair terms in the total $U$?
AB, AC, BC.
Opposite charges released from rest will:
Lower energy.
Ready for more? Take the Unit 9 test.