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A force F acts between two charges kept 1 cm apart in air. If permittivity of air and dielectric constant of water are $\in _0$ and $K$ respectively, find the force acting when both atoms are placed in water.

$(A)\;\frac{F}{K}\\ (B)\;\frac{F \in _0}{K} \\ (C)\; \frac{F}{K \in _0}\\ (D)\;\frac{FK}{\in _0} $

1 Answer

Force in air $F= \large\frac{1}{4 \pi \in _0} \frac{q_1q_2}{r^2}$
Force in water $F'= \large\frac{1}{4 \pi (k \in _0)} \frac{q_1q_2}{r^2}$
=> $F'= \large\frac{F}{K}$
Hence A is the correct answer.
answered Jan 3, 2014 by meena.p

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