Charges 3Q, q and Q are placed along x -axis at positions x = 0, x = 1/3 and x = 1 respectively. When the force on charge Q is zero, the value of q is (a) Q/3 (b) -Q/3 (c) 4/3Q (d) -4/3Q

Answer: (d). Force on Q (at x = 1) from 3Q (distance 1): (3kQ²)/(1²), along +x. Force on Q from q (distance 2/3): (kqQ)/((2/3)²) = 9kqQ/4, along the same line. Net zero: 3Q + 9q/4 = 0 ⇒ q = -4/3Q. So the answer is (d) -4/3Q.

Charges 3Q, q and Q are placed along x -axis at positions x = 0, x =… | MHT CET 2024 (11 May, Shift 1)

Q33MHT CET 2024 · 11 MAY · SHIFT 1Medium

Electric Charge & Coulomb's Law

Charges $3Q, q$ and Q are placed along x -axis at positions $x = 0, x = \frac{1}{3}$ and $x = 1$ respectively. When the force on charge Q is zero, the value of $q$ is

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Answer: (d)

Force on $Q$ (at $x = 1$ ) from $3Q$ (distance 1): $\dfrac{3kQ^2}{1^2}$ , along $+x$ .
Force on $Q$ from $q$ (distance $\tfrac{2}{3}$ ): $\dfrac{kqQ}{(2/3)^2} = \dfrac{9kqQ}{4}$ , along the same line.
Net zero: $3Q + \dfrac{9q}{4} = 0 \Rightarrow q = -\dfrac{4}{3}Q$ .
So the answer is (d) $-\dfrac{4}{3}Q$ .

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Electric Charge & Coulomb's Law question from MHT CET 2024 (11 May, Shift 1)

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