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Question: Answered & Verified by Expert
Two long conductors, separated by a distance $\mathrm{d}$ carry current $\mathrm{I}_1$ and $\mathrm{I}_2$ in the same direction. They exert a force $F$ on each other. Now the current in one of them increased to two times and its direction reversed. The distance is also increased to $3 \mathrm{~d}$. The new value of the force between them is
PhysicsMagnetic Effects of CurrentJEE MainJEE Main 2004
Options:
  • A
    $-2 \mathrm{~F}$
  • B
    $\mathrm{F} / 3$
  • C
    $-2 F / 3$
  • D
    $-\mathrm{F} / 3$
Solution:
1232 Upvotes Verified Answer
The correct answer is:
$-2 F / 3$
Force between two long conductor carrying current
$$
F=\frac{\mu_0}{2 \pi} \frac{l_1 l_2}{d} \ell
$$
According to question
$$
F^{\prime}=\frac{\mu_0}{2 \pi} \frac{\left(-2 I_1\right)\left(I_2\right)}{d} \ell
$$
From equation (i) and (ii), $\mathrm{F}^{\prime}=-\frac{3}{2} \mathrm{~F}$.

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