Two coils having self-inductances $\mathrm{L}_1=75 \mathrm{mH}$ and $L_2=48 \mathrm{mH}$ are coupled with each other. If the mutual inductance of the coils is 37.2 mH , then coefficient of coupling will be

An elastic conducting material is stretched into a circular loop. It is placed with its plane perpendicular to uniform magnetic field $\mathrm{B}=0.6 \mathrm{~T}$. When loop is released, the radius starts shrinking at constant rate $3 \mathrm{~cm} / \mathrm{s}$. The induced e.m.f. in the loop at an instant when the radius of the loop is 10 cm will be (in mV )

Two inductors of 88 mH each are joined in parallel. The current passing through this combination is 4 A . The energy stored in this combination of inductors in joule is

A bicycle wheel of diameter ' $D$ ' has ' $N$ ' number of spokes. Wheel is rotating at the rate of ' $x$ ' revolutions per minute, perpendicular to the horizontal component of earth's magnetic field ' $\mathrm{B}_{\mathrm{H}}$ '. The e.m.f. induced between the rim and the centre of the wheel will be