The correct answer is: B. Eddy current losses.
Laminating the core of a D.C. generator significantly reduces eddy current losses. Eddy currents are induced currents that flow in a closed loop within a conductor. They are caused by a changing magnetic field. The eddy currents cause heat to be generated, which can reduce the efficiency of the generator.
Laminating the core of the generator breaks up the magnetic field into smaller loops, which reduces the eddy currents and the amount of heat generated. This results in a more efficient generator.
Hysteresis losses are caused by the magnetic domains in the core of the generator realigning themselves with the changing magnetic field. These losses are proportional to the square of the magnetic field strength. Laminating the core does not reduce hysteresis losses.
Copper losses are caused by the resistance of the copper windings in the generator. These losses are proportional to the square of the current flowing through the windings. Laminating the core does not reduce copper losses.
Windage losses are caused by the friction of the air against the rotating parts of the generator. These losses are proportional to the square of the speed of rotation. Laminating the core does not reduce windage losses.