Question

A 1.0 µC point charge and a 7.0 µC point charge are a distance L apart. Where should a third point charge be placed so that the electric force on that third charge is zero? (Use the following as necessary: L.)

away from the 1.0 µC charge, ---Select--- between the charges on the far side of the 1 µC charge on the far side of the 7 µC charge .

Answer 1

Given

q1 = 1 uC , q2 = 7 uC

Distance is L

Let the third charge be q placed at x cm from q1

The force on q due to q1 is

F1 = k*q*q1 / x²

F1 = k*q*(1 uC) / x² ----1

Force on q due to q2 is

F2 =  k*q*q2 / (L-x)²

F2 = k*q*(7 uC) / (L-x)² -------2

Since net electric force is zero.

F1 = F2

k*q*(1 uC) / x² = k*q*(7uC) / (L-x)²

(L-x)² = 7*x²

L - x = 7 * x

L = x*(1+7)

L = 3.64*x

x = 0.274*L

the charge should be placed at a distance of 0.274 L from the 1uC charge.