A circular loop of radius R is carrying current I. The ratio of magnetic field at the center of circular loop and at a distance R from the center of the loop on its axis is

A circular coil of radius 'r' is placed on another circular coil whose radius is 'R' and the current flowing through it is changing and their centers coincide. ($R \gg r$). If both the coils are coplanar, then the mutual inductance between them is proportional to

A graph of magnetic flux ($\Phi$) versus current (I) is shown for four inductors A, B, C, D. The smallest value of self inductance is for inductor.

In the given circuit, if $dI/dt = -1\ \text{A/s}$ then the value of $V_{AB}$ at this instant will be