Question

A square frame of side $\ell$ carries a current produces a field B at its centre. The same current is passed through a circular loop having same perimeter as the square. The field at its centre is B' ,the ratio of $\frac{B}{B'}$ is

• A. $\frac{8\sqrt2}{\pi^2}$
• B. $\frac{8}{\pi^2}$
• C. $\frac{\sqrt2}{\pi^2}$
• D. $\frac{\pi^2}{8\sqrt2}$

Answer 1

Answer: (A)

$\frac{8\sqrt2}{\pi^2}$

Answer 2

$B=4 \left[ \frac{\mu _0}{4 \pi r} (\sin\theta_1+\sin \,\theta _2)\right],B=\frac{\mu_0\,ni}{2r}$