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 experiences a force whose magnitude and direction are

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

Answer 1

The correct option is C 8F towards -q charge

Initially, force betwen 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

$F_{net}=F_A+F_C=K\frac{Q^2}{\left(\frac{r}{2}\right)}+\frac{K{Q}^2}{(\frac{r}{2}{)}^2}=8\frac{K{Q}^2}{r^2}=8F.$

(Direction is shown in figure)