Electric Potential Practice Test

Three point charges lie in the $xy$-plane: $q_1=+2.0\times10^{-9}\ \text{C}$, $q_2=-2.0\times10^{-9}\ \text{C}$, and $q_3=+1.0\times10^{-9}\ \text{C}$. A point $P$ is $0.30\ \text{m}$ from $q_1$, $0.30\ \text{m}$ from $q_2$, and $0.20\ \text{m}$ from $q_3$. Use superposition with $V=\sum kq_i/r_i$ (and $k=8.99\times10^{9}$, $e=1.60\times10^{-19}\ \text{C}$). In the situation described, what is the electric potential at point $P$ due to the charge configuration?

A uniform electric field $E=1.2\times10^{3},\text{N/C}$ points upward. Points $A$ and $B$ are separated vertically by $d=0.50,\text{m}$, with $B$ above $A$. Use $\Delta V=V_B-V_A=-Ed$. Based on the data, calculate the potential difference between points $A$ and $B$.