Two particles A and B having charges 20 μ C and -5μ C respectively… | JEE Main 2021 (31 Aug, Shift 1)

Q56JEE Main 2021 · 31 AUG · SHIFT 1Easy

Electric Charge & Coulomb's Law

Two particles A and B having charges 20 $\mu$ C and $-5\mu$ C respectively are held fixed with a separation of 5 cm. At what position a third charged particle should be placed so that it does not experience a net electric force?

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Answer: (b)

Unlike charges: the null point lies outside, nearer the smaller charge ( $-5\ \mu\text{C}$ at B), i.e. to the right of B.
Let it be $x$ cm right of B: $\dfrac{20}{(5+x)^2} = \dfrac{5}{x^2}$
$\dfrac{5+x}{x} = 2 \Rightarrow x = 5\ \text{cm}$
So the answer is (b) at 5 cm from $-5\ \mu\text{C}$ on the right side.

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