In an inductor of self-inductance $$2 \mathrm{~mH}$$, current changes with time (in sec) according to the relation, $$I=(3 t^2-3 t+8) A$$. The emf becomes zero at

A metallic rod of length '$$a$$' is rotated with an angular frequency of $$0.2 \mathrm{~rads}^{-1}$$ about an axis normal to the rod passing through its one end. A constant and uniform magnetic field of '$$\mathrm{B}$$' T parallel to the axis exists everywhere. The emf developed across the ends of the rod is

Select the unit of the coefficient of mutual induction from the following.

Around the central part of an air cored solenoid of length $$20 \mathrm{~cm}$$ and area of cross section $$1.4 \times 10^{-3} \mathrm{~m}^2$$ and 3000 turns, another coil of 250 turns is closely wound. A current $$2 \mathrm{~A}$$ in the solenoid is reversed in $$0.2 \mathrm{~s}$$, then the induced emf produced is