Two small spherical balls each carrying a charge Q=10μC (10 micro-coulomb) are suspended by two insulating threads of equal lengths 1m each, from a point fixed in the ceiling. It is found that in equilibrium threads are separated by an angle 60o between them, as shown in the figure. What is the tension in the threads (Given: 1(4πε0)=9×109Nm/C2)

A
18 N
B
1.8 N
C
0.18 N
D
None of the above

Solution:

In the following figure, in equilibrium $F_{e} = T \sin 30^{o}, r = 1 m$

$\begin{array}{l} \Rightarrow 9 \times 10^{9} \cdot \frac{Q^{2}}{r^{2}} = T \times \frac{1}{2} \\ \Rightarrow 9 \times 10^{9} \cdot \frac{{(10 \times 10^{- 6})}^{2}}{1^{2}} = T \times \frac{1}{2} \Rightarrow T = 1 .8 N \end{array}$

Solution:

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