Question

A point charge has a charge of 2.50 X 10-11 C. At what distance from the point charge is the electric potential a) 90.0 V? b) 30.0 V? Take the potential to be zero at an infinite distance from the charge.

Note: Show your free body diagram (FBD) and solutions accurately, systematically and orderly with the standard unit, and express it into prefix word if possible.

Answer 1

Potential due to a point charge is given by $\frac{kQ}{r}$

where k= $9\times10^9$

let's deduce a equation of V in terms of r :

$V=\frac{9\times10^9\times2.5\times10^{-11}}{r}$

$r=\frac{0.225}{V}$

a) when V = 90 volts

$r=0.225/90=0.0025m$

b) when V = 30 volts

$r=0.225/30=0.0075m$