Answer 1

The net magnetic flux (Φ_B) through any closed surface is always zero.

This law suggests that the number of magnetic field lines leaving any closed surface is always equal to the number of magnetic field lines entering it.

Suppose a closed surface S is held in a uniform magnetic field `vecB`.

Consider a small vector area element Δ`vec"S"` of this surface.

Magnetic flux through this area element is defined as ΔΦ_B = `vec"B".Δvec"S" `

Considering all small area elements of the surface, we obtain net magnetic flux through the surface as:

Ø_B = `sum_"All" ΔØ_"B"  = sum_"All" vec"B". Δvec"S" = 0`