magnetic lines behave like a stretched band.why is it so?

Question

shayaan_mustafa · Answer

kindly elaborate your question.
Thanks

anonymous · Answer

Because there are no magnetic monopoles.  That is, there is no such thing as a magnetic "charge," the way there are electrical charges, which can serve as a source or sink of magnetic field lines.  WIthout a place for the field lines to start or stop, all field lines must be closed loops at all times.  They act like stretchy bands because a larger loop means a stronger magnetic field at the source (which is some electrical current).  So increasing the size of a loop takes work (extra current), and shrinking the loop releases energy (as the magnetic field energy converts back to electric current).