🔍 Key Concepts
• Brush sparking causes in DC machines (motors and generators)
• Effect of brush pressure, alignment, and wear on commutation
• How commutator surface condition (dirt, eccentric wear, high mica, uneven bar height) affects sparking
💭 Think About
• Which of the listed conditions would disturb the smooth transfer of current from one commutator bar to the next at the brushes?
• Do the options in A, B, and C describe different types of mechanical or electrical problems, or are they overlapping causes of the same symptom (sparking)?
• If each individual item in A, B, and C can reasonably cause sparking, what does that suggest about an option that tries to combine them?
✅ Before You Answer
• For each bullet in A, B, and C, ask: "Would this increase resistance, cause arcing, or disturb contact at the brush/commutator interface?"
• Confirm that you understand "neutral point" and why setting brushes off-neutral affects commutation in a DC machine.
• Before choosing, check whether any one of A, B, or C includes a condition that is not a realistic cause of brush sparking; if all listed conditions are valid causes, that affects how you view option D.