Question

Suppose you have a 66.0 nC point charge and you measure a potential of 291 V. At
what distance from the charge did you make the measurement?

Answer 1

The potential of the point charge is:

$\varphi = k\dfrac{q}{r}$ ,

where $q$ is the charge, $r$ is the distance from charge to the point of measurement and $k = 9×10^9 N⋅m^2⋅C^{−2}$ is the Coulomb's constant. Express $r$ from this formula ans substitute numerical values:

$r = k\dfrac{q}{\varphi} = 9\cdot 10^9 \dfrac{66\cdot 10^{-9}}{291} = 2.04 m$.

Answer. r = 2.04 m.