Electrostatics Question 437
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 1m each, from a point fixed in the ceiling. It is found that in equilibrium threads are separated by an angle $ 60^{o} $ between them. What is the tension in the threads (Given: $ \frac{1}{(4\pi {\varepsilon _{0}})}=9\times 10^{9}Nm/C^{2} $ ) [MP PET 2001; Pb PET 2003]
Options:
A) 18 N
B) 1.8 N
C) 0.18 N
D) None of the above
Show Answer
Answer:
Correct Answer: B
Solution:
In equilibrium $ F _{e}=Tsin30^{o} $ , r = 1m therefore $ 9\times 10^{9}.\frac{Q^{2}}{r^{2}} $ =$ T\times \frac{1}{2} $
therefore $ 9\times 10^{9}.\frac{{{(10\times {{10}^{-6}})}^{2}}}{1^{2}}=T\times \frac{1}{2} $
$ \Rightarrow $ T = 1.8 N
