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JEE Main 2013 (9 Apr, Shift 1) · Electric Charge & Coulomb's Law

Electric Charge & Coulomb's Law question from JEE Main 2013 (9 Apr, Shift 1)

Q72JEE Main 2013 · 9 APR · SHIFT 1Medium

Electric Charge & Coulomb's Law

Two balls of same mass and carrying equal charge are hung from a fixed support by threads of length $l$ . At electrostatic equilibrium, assuming that angles made by each thread is small, the separation, x between the balls is proportional to:

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Answer: (d)

Small angle: $\tan\theta \approx \dfrac{x}{2l} = \dfrac{F}{mg} = \dfrac{kq^2}{x^2 mg}$ .
$x^3 = \dfrac{2kq^2 l}{mg} \Rightarrow x \propto l^{1/3}$
So the answer is (d) $l^{1/3}$ .

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