Electric potential at a point 'P' due to a point charge of 5 × 10^...

Electric potential at a point P due to a point charge, \left(\because \mathrm{K}=9 \times 10^9\right)V_P=\frac{K Q}{r}\Rightarrow \quad 50=\frac{9 \times 10^9 \times 5 \times 10^{-9}}{\mathrm{r}}\Rightarrow \quad \mathrm{r}=\frac{45}{50}=\frac{9}{10}=0.9 \mathrm{ m}=90 \mathrm{ cm}