Question

Two small spheres each having equal positive charge $Q$ (Coulomb) on each are suspended by two insulating strings of equal length $L$ (metre) from a rigid hook (shown in figure). The whole set up is taken into satellite where there is no gravity. The two balls are now held by electrostatic forces in horizontal position, the tension in each string is then

• A. $\frac{Q^2}{16\pi {\epsilon }_0{L}^2}$
• B. $\frac{Q^2}{8\pi {\epsilon }_0{L}^2}$
• C. $\frac{Q^2}{4\pi {\epsilon }_0{L}^2}$
• D. $\frac{Q^2}{2\pi {\epsilon }_0{L}^2}$

Answer 1

Answer: (A)

In this case, tension will be equal to force

The tension in each string
$T=F$
$=\frac{1}{4\pi {\epsilon }_0}\frac{Q^2}{(2L{)}^2}$
$=\frac{Q^2}{16\pi {\epsilon }_0{L}^2}$