The magnetic energy stored in an inductor of inductance $5 \mu \mathrm{H}$ carrying a current of 2 A is

A bicycle wheel of radius ' $R$ ' has ' $n$ ' spokes. It is rotating at the rate of ' $F$ ' r.p.m. perpendicular to the horizontal component of earth's magnetic field $\vec{B}$. The e.m.f. induced between the rim and the centre of the wheel is

A long solenoid has 1500 turns. When a current of $$3.5 \mathrm{~A}$$ flows through it, the magnetic flux linked with each turn of solenoid is $$2.8 \times 10^{-3}$$ weber. The self-inductance of solenoid is

A coil having effective area A, is held with its plane normal to magnetic field of induction B. The magnetic induction is quickly reduced by $$25 \%$$ of its initial value in 2 second. Then the e.m.f. induced across the coil will be