What is the electric potential at the point indicated with the dot in (Figure 1)?

### Answer

We have: AB = 3.0cm = CD

and

AD = BC = 4cm

and

```
A D^{2}+D C^{2}=A C^{2} \quad 2
\Rightarrow \quad A C^{2}=3^{2}+4^{2}=25 \Rightarrow \quad A C=5 \mathrm{~cm}
```

Now electric potential at point C =>

```
\begin{aligned}
V_{c} &=\frac{K\left(2 \times 10^{-9}\right)}{D C}+\frac{K\left(2 \times 10^{-9}\right)}{A C}+\frac{k\left(2 \times 10^{-9}\right)}{B C} \\
&=9 \times 10^{9} \times\left(2 \times 10^{-9}\right)\left[\frac{1}{3 \times 10^{-2}}+\frac{1}{5 \times 10^{-2}}+\frac{1}{4 \times 10^{-2}}\right] \\
&=18\left[\frac{20+12+15}{60 \times 10^{-2}}\right] \\
&=\frac{18 \times 47 \times 10^{2}}{60}=1410
\end{aligned}
```