A straight section PQ of a circuit lies along the X-axis from $\mathrm{x}=-\frac{\mathrm{a}}{2}\mathrm{to}\mathrm{x}=\frac{\mathrm{a}}{2}$ and carries a steady current i. The magnetic field due to the section PQ at a point X = + a will be

• A

  Proportional to a

• B

  Proportional to a²

• C

  Proportional to 1/a

• D

  Zero