Q.Three point charges $q_1 = +1\ \mu\text{C}$, $q_2 = -2\ \mu\text{C}$ and $q_3 = +3\ \mu\text{C}$ are situated at distances of $1\ \text{m}$, $2\ \text{m}$ and $3\ \text{m}$ respectively from a point $P$. Find the net electric potential at $P$.

Using superposition, $V_P = k(q_1/r_1 + q_2/r_2 + q_3/r_3)$ with $q_1=1\ \mu\text{C}, r_1=1\ \text{m}$; $q_2=-2\ \mu\text{C}, r_2=2\ \text{m}$; $q_3=3\ \mu\text{C}, r_3=3\ \text{m}$:

$\frac{q_1}{r_1} = 1\times 10^{-6},\quad \frac{q_2}{r_2} = -1\times 10^{-6},\quad \frac{q_3}{r_3} = 1\times 10^{-6}$ …

Compute each $q_i/r_i$ term separately, keeping signs, the …

• Vector-adding the contributions (as if finding a resultant field) instead of simply adding the (signed) numbers -- potential is a scalar sum. …