A very long cylindrical wire of radius R carries a current  ${\mathrm{I}}_0$ uniformly distributed across the cross-section of the wire. Calculate the magnetic flux through a rectangle that has one side of length w running down the centre of the wire and another side of length R, as shown in figure.

• A

  $\frac{{\mathrm{\mu }}_0{\mathrm{I}}_0\mathrm{w}}{4\mathrm{\pi }}$

• B

  $\frac{{\mathrm{\mu }}_0{\mathrm{I}}_0\mathrm{wR}}{4\mathrm{\pi }}$

• C

  $\frac{{\mathrm{\mu }}_0{\mathrm{I}}_0\mathrm{R}}{4\mathrm{\pi w}}$

• D

  None