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

  • [JEE MAIN 2022]
  • A

    $B / 2$

  • B

    $2 B$

  • C

    $\left(\frac{2}{\sqrt{5}}\right)^{3} B$

  • D

    $\left(\frac{2}{\sqrt{3}}\right)^{3} B$

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  • [JEE MAIN 2022]