The number of turns of primary and secondary coils of a transformer are $5$ and $10$ respectively and the mutual inductance of the transformer is $25\,henry$. Now the number of turns in the primary and secondary of the transformer are made $10$ and $5$  respectively. The mutual inductance of the transformer in henry will be

In $SI$, Henry is the unit of

If the current $30 \,A$ flowing in the primary coil is made zero in $0.1 \,sec$. The $e.m.f.$ induced in the secondary coil is $1.5 \,volt$. The mutual inductance between the coil is.....$H$

Two coils of self inductance $2\,\,mH$ and $8\,\,mH$ are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is......$  mH$

A circular loop of radius $0.3\, cm$ lies parallel to a much bigger circular loop of radius $20 \,cm$. The centre of the small loop on the axis of the bigger loop. The distance between their centres is $15\, cm$. If a current of $20\, A$ flows through the smaller loop, then the flux linked with bigger loop is

Two circular coils have their centres at the same point. The mutual inductance between them will be maximum when their axes