A coil is wound on a transformer of rectangular cross-section. If all the linear dimensions of the transformer are increased by a factor 2 and the number of turns per unit length of the coil remain the same, the self-inductance is increased by a factor of
Self-inductance,
Where n is the number of turns per unit length and N is the total number of turns, i.e., N = nl
In the given question n is same. A is increased 4 times and l is increased 2 times and hence L will be increased 8 times.