The correct answer is: B. Decrease
A DC generator is a device that converts mechanical energy into electrical energy. It does this by using a rotating magnetic field to induce an electric current in a stationary coil of wire. The strength of the induced current is proportional to the strength of the magnetic field and the number of turns in the coil.
The resistance of the field winding is the resistance of the wire that is used to create the magnetic field. If the resistance of the field winding is increased, the current that flows through the winding will decrease. This will decrease the strength of the magnetic field, which will in turn decrease the induced current in the coil.
Therefore, if the resistance of the field winding is increased, the output voltage of the generator will decrease.
Option A is incorrect because increasing the resistance of the field winding will decrease the current that flows through the winding, which will in turn decrease the strength of the magnetic field. This will decrease the induced current in the coil, and therefore the output voltage of the generator.
Option C is incorrect because increasing the resistance of the field winding will decrease the current that flows through the winding, which will in turn decrease the strength of the magnetic field. This will decrease the induced current in the coil, and therefore the output voltage of the generator.
Option D is incorrect because increasing the resistance of the field winding will not cause the output voltage to fluctuate heavily. The output voltage will decrease, but it will not fluctuate.