Q.For the same short bar magnet of Numerical 3 ($m = 0.9\ \text{A}\cdot\text{m}^2$), calculate the magnitude and direction of the magnetic field at a point on its equatorial line at the same distance of $10\ \text{cm}$ from its centre.

Modelling a short bar magnet as two poles $\pm q_m$ a distance $2l$ apart (dipole moment $m=q_m(2l)$, from S to N), the field it produces at a point far away ($d\gg l$) along its own AXIS is $B_{\text{axial}}=(\mu_0/4\pi)(2m/d^3)$, directed along $\vec{m}$; on its EQUATORIAL line (the perpendicular bisector of the S-N line) it is $B_{\text{eq}}=(\mu_0/4\pi)(m/d^3)$, directed opposite to $\vec{m}$ and exactly HALF the axial …