Electrostatics Question 498
Question: A pendulum bob of mass $ 30.7\times {{10}^{-6}}kg $ and carrying a charge $ 2\times {{10}^{-8}}C $ is at rest in a horizontal uniform electric field of 20000 V/m. The tension in the thread of the pendulum is $ (g=9.8m/s^{2}) $ [UPSEAT 2004]
Options:
A) $ 3\times {{10}^{-4}}N $
B) $ 4\times {{10}^{-4}}N $
C) $ 5\times {{10}^{-4}}N $
D) $ 6\times {{10}^{-4}}N $
Show Answer
Answer:
Correct Answer: C
Solution:
$ T=\sqrt{{{(mg)}^{2}}+{{(QE)}^{2}}} $
$ =\sqrt{{{(30.7\times {{10}^{-6}}\times 9.8)}^{2}}+{{(2\times {{10}^{-8}}\times 20000)}^{2}}} $
$ =5\times {{10}^{-4}}N $
