The ratio of magnetic induction on the axis of a circular current carrying coil of radius r to the magnetic induction at its centre will be

• A

  $\frac{1}{{\left(1+\frac{{\mathrm{x}}^2}{{\mathrm{r}}^2}\right)}^{3/2}}$

• B

  $\frac{1}{{\left(1+\frac{{\mathrm{x}}^2}{{\mathrm{r}}^2}\right)}^{1/2}}$

• C

  $\frac{1}{{\left(1-\frac{{\mathrm{X}}^2}{{\mathrm{r}}^2}\right)}^{-3/2}}$

• D

  $\frac{1}{{\left(1+\frac{{\mathrm{X}}^2}{{\mathrm{r}}^2}\right)}^{-1/2}}$