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Question: Answered & Verified by Expert
Two long straight parallel conductors are carrying currents $i_1$ and $i_2$ in the same direction. Work done per unit length, when the distance between them is doubled is
PhysicsMagnetic Effects of CurrentAP EAMCETAP EAMCET 2018 (23 Apr Shift 2)
Options:
  • A $2 \times \frac{\mu_0}{2 \pi} i_1 i_2$
  • B $\frac{\mu_0}{2 \pi} i_1 i_2 \ln [2]$
  • C $\frac{\mu_0}{2 \pi} i_1 i_2 \ln [4]$
  • D 0
Solution:
1982 Upvotes Verified Answer
The correct answer is: $\frac{\mu_0}{2 \pi} i_1 i_2 \ln [2]$
$\begin{aligned} \text { Work done } & =\int_d^{2 d} F \cdot d x=\int_d^{2 d} \frac{\mu_0 i_1 i_2}{2 \pi x} \cdot d x \\ & =\frac{\mu_0 i_1 i_2}{2 \pi}\left[\log _e x\right]_d^{2 d}=\frac{\mu_0 i_1 i_2}{2 \pi}\left(\log _e 2\right)\end{aligned}$

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