Question

A current carrying coil is bent sharply, So as to convert it into a double loop both carrying current in the same direction if $B$ be the initial magnetic field at the center. What will be the final concentric magnetic field.

• A. $2B$
• B. $4B$
• C. $8B$
• D. $Zero$

Answer 1

The correct option is B $4B$

$\text{Given}$ : B is the initial magnetic field at the center

$\text{To find}$ : the final concentric magnetic field.

$\text{Solution}$ :

Radius of the double loop, r = $\frac{R}{2}$

Where R is the radius of single loop.

Now, $B_{centre}$= $\frac{{\mu }_o}{4\pi }\times \frac{2\pi I}{R}$

So, magnetic field due to each coil is double of that due to single coil.

and total magnetic field
=2B+2B=4B

$\text{Hence option B is correct}$