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. $\frac{B}{2}$
• B. $2B$
• C. $B$
• D. $4B$

Answer 1

The correct option is C $B$

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

$B=\frac{{\mu }_{0}2I}{2\pi r}-\frac{{\mu }_{0}I}{2\pi r}=\frac{{\mu }_{0}I}{2\pi r}$

When current $2I$ is switched off then magnetic field due to conductor carrying current $I$ is

$B=\frac{{\mu }_{0}I}{2\pi r}$.