Question

Two small spherical balls each carrying a charge Q = 10$\mu C$ (10 micro-coulomb) are suspended by two insulating threads of equal lengths 1 m each, from a point fixed in the ceiling. It is found that in equilibrium threads are separated by an angle 60⁰ between them, as shown in the figure. What is the tension in the threads. (Given : $\frac{1}{\left( 4\pi\varepsilon_{0} \right)} = 9 \times 10^{9}Nm/C^{2}$)

• A. 8 N
• B. 1.8 N
• C. 18 N
• D. None of these

Answer 1

Answer: (B)

1.8 N

Answer 2

From the geometry of figure

r = 1m

In the condition of equilibrium $T\sin 30^{o} = F_{e}$

$T \times \frac{1}{2} = 9 \times 10^{9}.\frac{(10 \times 10^{- 6})^{2}}{1^{2}}$

$\Rightarrow$T= 1.8 N