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A long copper wire is wound uniformly on a cylindrical spool of radius R = 1.0 cm and relative magnetic permeability , = 150. The winding thus forms a solenoid with a number of turns per unit of length n = 500 turns / m; it is traversed by a current i = 1.5 A which is kept constant by means of a suitable current generator. By applying a force to the free end of the copper wire, the spool rotates in the opposite direction to the winding and the wire begins to unwind. Assuming that the spool rotation occurs at constant angular speed w = 360 rad s 1 calculate: a) the induced electromotive force present at the ends of the solenoid; b) the total amount of energy that the generator must put into play in one revolution of the reel; c) the energy variation within the solenoid after 10 turns. Assume that the length of the solenoid is much larger than its radius.