The magnetic lines of force inside a bar magnet

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon

When the current changes from $$ + 2A$$ to $$-2A$$ in $$0.05$$ second, an $$e.m.f.$$ of $$8$$ $$V$$ is inducted in a coil. The coefficient of self- induction of the coil is

The core of any transformer is laminated so as to