According to Maxwell's second equation, the total magnetic flux passing through a closed surface is zero.

$∯\stackrel{\rightharpoonup }{B}.\stackrel{\rightharpoonup }{ds} = 0$

where $∯\stackrel{\rightharpoonup }{B}.\stackrel{\rightharpoonup }{ds}$ is the surface integral of the magnetic field over a closed surface. This law confirms that the magnetic field is generated due to the dipole nature of the magnet as the number of magnetic lines entering the surface is equal to the number of magnetic lines leaving it. Thus, magnetic lines form closed loops and no isolated magnetic monopole can exist.