The energy required to build up a current I in a coil of self-inductance L is:

A conducting ring of radius r is placed in a varying magnetic field perpendicular to the plane of the ring. If the rate at which the magnetic field varies is x, the electric field intensity at any point of the ring is ____________.
Fill in the blank with the correct answer from options given below.

A 50 Hz ac current of crest value 1A flows through the primary of a transformer. If the mutual inductance between the primary and secondary be 0.5 H, the crest voltage in the is ___________.
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A long solenoid of diameter 0.1 m has turns per meter. At the centre of the solenoid a coil of 100 turns and radius 0.01 m is placed with is axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to 0 A from 4 A in 0.05 s. If the resistance of the coil is then the total charge flowing through the coil during this time is ____________.
Fill in the blank with the correct answer from the options given below.