Question

Two long parallel wires carry currents $i$ and $2i$ in the same direction. Magnetic field between the wire is B. If the current in the second wire, $2i$ is switched off, then magnetic field at the same point is

• A. 2B
• B. B
• C. B/2
• D. $\sqrt{2}B$

Answer 1

The correct option is B B

When two parallel conductors carrying current I and 2I in same direction, then magnetic field at the midpoint is $B=\frac{{\mu }_{0}2l}{2\pi r}-\frac{{\mu }_{0}I}{2\pi r}=\frac{{\mu }_{0}I}{2\pi r}$ When current 2I is switched off then magnetic field due to conductor carrying current I is $B=\frac{{\mu }_{0}I}{2\pi r.}$