Question

A wire carrying current I and other carrying $ 2I $ in the same direction produce a magnetic field B at the mid-point. What will be the field when $ 2I $ wire is switched off?

• A. $ B/2 $
• B. $ 2B $
• C. $ B $
• D. $ 4B $

Answer 1

Answer: (C)

When two parallel conductors carrying current $I$ and $2 I$ in the same direction, then magnetic field at the mid-point is

$B=\frac{\mu_{0} 2 I}{2 \pi r}-\frac{\mu_{0} I}{2 \pi r}=\frac{\mu_{0} I}{2 \pi r}$
When current $2 I$ is switched off then magnetic field due to conductor carrying current $I$ is $B=\frac{\mu_{0} I}{2 \pi r} .$