The loop ABC, has the shape of an isoceles right angled triangle. If is carrying a current i. If AB = BC = l, then induction at D is

• A

  $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{i}}{2\sqrt{2}\mathrm{\pi l}}$

• B

  $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{i}}{2\mathrm{\pi a}}\left(1+\frac{1}{\sqrt{2}}\right)$

• C

  $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{i}}{4\mathrm{\pi a}}\left(1+\frac{1}{\sqrt{2}}\right)$

• D

  $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{i}}{4\mathrm{\pi l}}[\sqrt{2}-2]$