Question

Two long wires one carrying current 1 A and other carrying 2 A in the same direction are placed parallel to each other produces a net magnetic field B at the mid-point. What will be the field at mid-point when current 1 A is switched off?

• A. $B$
• B. $2B$
• C. $\frac{B}{2}$
• D. $\frac{3B}{2}$

Answer 1

The correct option is B $2B$

Given : $I_1=1A$ and $I_2=2A$

Magnetic field $B$ at center.

Solution :

Magnetic field due to long current carrying wire is $\frac{{\mu }_{0}I}{2\pi r}$

$B_1=\frac{{\mu }_0\cdot 1}{2\pi r}T⨂$ , where r is the distance between center and the wire 1

$B_2=\frac{{\mu }_0\cdot 2}{2\pi r}T⨀$ , where r is the distance between center and the wire 2

Hence, $B=\frac{{\mu }_0\cdot 2}{2\pi r}-\frac{{\mu }_0\cdot 1}{2\pi r}=\frac{{\mu }_0\cdot 1}{2\pi r}T⨀$

$B_2=2B$

The correct Opt : {B}