Question

Two similar spheres having +q and -q charge are kept at a certain distance. F force acts between the two. If in the middle of two spheres, another similar sphere having +q charge is kept, then it experience a force in magnitude and direction as

• A. Zero having no direction
• B. 8 F towards +q charge
• C. 8 F towards -q charge
• D. 4 F towards +q charge

Answer 1

The correct option is C 8 F towards -q charge

Initially, force between A and C $F=k\frac{Q^2}{r^2}$


When a similar sphere B having charge +Q is kept at the mid point of line joining A and C, then Net force on B is
$F_{net}=F_A+F_C=k\frac{Q^2}{{\left(\frac{r}{2}\right)}^2}+\frac{k{Q}^2}{{\left(\frac{r}{2}\right)}^2}=8\frac{k{Q}^2}{r^2}=8F$.
(Direction is shown in figure)