Electrostatics Question 451

Question: The distance between charges $ 5\times {{10}^{-11}}C $ and $ -2.7\times {{10}^{-11}}C $ is 0.2 m. The distance at which a third charge should be placed in order that it will not experience any force along the line joining the two charges is [Kerala PET 2002]

Options:

A) 0.44 m

B) 0.65 m

C) 0.556 m

D) 0.350 m

Show Answer

Answer:

Correct Answer: C

Solution:

If two opposite charges are separated by a certain distance, then for it’s equilibrium a third charge should be kept outside and near the charge which is smaller in magnitude.

Here, suppose third charge q is placed at a distance x from $ 2.7\times 10^{11}C $ then for it’s equilibrium $ | F _{1} |=| F _{2} | $

therefore $ \frac{kQ _{1}q}{{{(x+0.2)}^{2}}}=\frac{kQ _{2}q}{x^{2}} $

therefore x = 0.556 m $ ( \text{Here }k=\frac{1}{4\pi {\varepsilon _{0}}}\text{and}Q _{1}=5\times {{10}^{-11}}C,Q _{2}=-2.7\times {{10}^{-11}}C ) $



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