Question 428Electricity & Electronics - Assistant Engineer

The correct answer is D. The reason is that there is an optimal pressure range for DC generator brushes that results in minimal brush wear. Brush pressures above the optimal range cause excessive mechanical wear, as the brushes are pressing too hard against the commutator, leading to faster abrasion. Conversely, brush pressures below the optimal range cause excessive electrical wear, as the brushes are not making proper contact with the commutator, leading to increased arcing and burning. The other options are incorrect because A incorrectly states that the wear rate is proportional to brush pressure, and B incorrectly states that the wear rate is inversely proportional to brush pressure. Option C is incorrect because it incorrectly describes the effects of brush pressure above and below the optimal range.