If four charges \(+12\,\text{nC}, -20\,\text{nC}, +32\,\text{nC}\) and \(-15\,\text{nC}\) are arranged at the four vertices of a square of side \(\sqrt{2}\,\text{m}\), then the net electric potential at the centre of the square due to these four charges is
Show Hint
Electric potential is a scalar quantity, so it can be added algebraically even if the charges are at different locations.
Step 1: The distance of the centre of the square from each vertex is:
\[
r = \frac{\sqrt{2}}{2} = \frac{1}{\sqrt{2}}\,\text{m}
\]
Step 2: Use the formula for electric potential at a point:
\[
V = \frac{1}{4\pi \varepsilon_0} \sum \frac{q_i}{r}
\]
Step 3: Total charge:
\[
q_{\text{net}} = (+12 - 20 + 32 - 15)\,\text{nC} = 9\,\text{nC} = 9 \times 10^{-9}\,\text{C}
\]
Step 4: Electric potential:
\[
V = \frac{1}{4\pi \varepsilon_0} . \frac{9 \times 10^{-9}}{1/\sqrt{2}} = 9 \times 10^9 . 9 \times 10^{-9} . \sqrt{2} = 81 \sqrt{2} \approx 81\,\text{V}
\]