Question

Magnetic field due to two current carrying conductors of the same length at the same point is $B$ and $\frac{B}{4}$ respectively when they are placed near the point one after the other. Now, if the direction of current of the first conductor is reversed, then the value of respective magnetic fields will be:

$($Here, negative sign represents the reversal of direction of the magnetic field$)$

• A. $-B,-\frac{B}{4}$
• B. $B,-\frac{B}{4}$
• C. $-B,\frac{B}{4}$
• D. $B,\frac{B}{4}$

Answer 1

The correct option is C $-B,\frac{B}{4}$

Given:

${\overrightarrow{B}}_1=B$ and ${\overrightarrow{B}}_2=\frac{B}{4}$

As the direction of current is reversed in the first conductor only, then, from right-hand thumb rule, the direction of magnetic field will also get reversed.

Hence, ${\overrightarrow{B}}_1^{{}^{\prime }}=-B$

But, the direction of magnetic field due to the second conductor will remain the same.

$i.e.{\overrightarrow{B}}_2^{{}^{\prime }}=\frac{B}{4}$

Hence, option $\left(c\right)$ is the correct answer.