(a) Gauss’s law of magnetism: It states that the net magnetic flux out of any closed surface is zero. That is, the number of magnetic field lines entering any closed surface is equal to the number of magnetic field lines leaving the closed surface.
Significance of Gauss’s law of magnetism: It amounts to a statement that there are no magnetic mono poles. For dipole, any closed surface has magnetic flux towards inward direction to south pole and equal flux towards outward direction to north pole.
In the case of mono poles, magnetic flux is not zero and hence it is a fact that mono poles does not exist.
(b) Properties of magnetic field lines due to a bar magnet:
(i) Magnetic field lines are closed continuous curves.
(ii) No two magnetic field lines can intersect.
(iii) Tangent to magnetic field lines at any point gives the direction of magnetic field strength at that point.
(iv) Large and closely arranged magnetic field lines represent stronger magnetic field and vice versa.
