Question

A +2nC point charge is 1cm below while a −2nC point charge is 1cm to the right of a third point charge q as shown in Figure 1 If q = 3 μC , what is the magnitude of the net electric force acting on it? (Please notice the different unit for q.)

Answer 1

F2 0.01m 0.01m F1 q1-2nC

Electric Force, $F=kq_{1}q_{2}/r^{2}$

$F_{1}=kq_{1}q/r^{2}$

$F_{1}=9*10^{9}*2*10^{-9}C*3*10^{-6}C/(0.01m)^{2}$

$F_{1}=9*10^{9}*2*10^{-9}*3*10^{-6}/0.01^{2}$

$F_{1}=0.54N$

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$F_{2}=kq_{2}q/r^{2}$

Since charges and distance are same

$F_{2}=F_{1}=0.54N$

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Net Force, $F=\sqrt{F_{1}^{2}+F_{2}^{2}}$

$F=\sqrt{(0.54N)^{2}+(0.54N)^{2}}$

ANSWER: $F=0.764N$

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