Carbon brushes are ______.

Carbon brushes are ______.

• A. rigid
• B. porous
• C. conductive
• D. brittle

Answer: (B)

Carbon brushes are porous. The carbon-graphite composite used for brushes has an open, porous structure that lets lubricant or graphite remain in the material as the brush slides against the rotating commutator. This porosity provides self-lubrication, helps manage wear by giving space for debris, and helps maintain a consistent sliding contact and heat dissipation over time. While conductivity is essential for carrying current, the porous nature specifically enables the brush to perform reliably under sliding contact, making it the defining trait described here.

Carbon brushes are porous. The carbon-graphite composite used for brushes has an open, porous structure that lets lubricant or graphite remain in the material as the brush slides against the rotating commutator. This porosity provides self-lubrication, helps manage wear by giving space for debris, and helps maintain a consistent sliding contact and heat dissipation over time. While conductivity is essential for carrying current, the porous nature specifically enables the brush to perform reliably under sliding contact, making it the defining trait described here.