The magnetic field at the centre of a circular coil of radius $I$, due to current I flowing through it, is $B$. The magnetic field at a point along the axis at a distance $\frac{r}{2}$ from the centre is
  • A$B / 2$
  • B$2 B$
  • C$\left(\frac{2}{\sqrt{5}}\right)^{3} B$
  • D$\left(\frac{2}{\sqrt{3}}\right)^{3} B$
JEE MAIN 2022, Medium
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