A short bar magnet has a length 2l and a magnetic moment 10Am² . Find the magnetic field at a distance of z = 0.1m from its centre on the axial line. Here, l is negligible as compared to z.

A. 2 × 10⁻³ T
B. 3 × 10⁻³ T
C. 1 × 10⁻³ T
D. 4 × 10⁻³ T