State the direction of the magnetic dipole moment (from $S$ to $N$ pole of the magnet) and write the unit of the magnetic dipole moment.

The magnetic field due to a short bar magnet of magnetic dipole moment $M$ and length $2l$,on the axis at a distance $Z$ (where $Z \gg l$) from the centre of the magnet is given by . . . . . . .

Magnetic field intensity is defined as

The magnetic field lines due to a bar magnet are correctly shown in

Use:
$(i)$ the Ampere's law for $\vec{H}$ and
$(ii)$ continuity of lines of $\vec{B}$,to conclude that inside a bar magnet,
$(a)$ lines of $\vec{H}$ run from the $N$ pole to $S$ pole,while
$(b)$ lines of $\vec{B}$ must run from the $S$ pole to $N$ pole.

Write a brief history of magnets.