🔍 Key Concepts

• Brush mounting types shown: radial, trailing, and leading mounts • How a reaction-type brush holder uses friction force from commutator rotation to change effective brush pressure • Direction of armature rotation vs the arrow for frictional force on the brush face

💭 Think About

• For each mounting (A, B, C), ask: does the friction force tend to push the brush farther into the holder (increasing pressure) or pull it out (reducing pressure)? • Which mounting arrangement would cause brush pressure to automatically increase with load and friction, rather than stay constant from only the spring? • Look for the figure where the line of friction and the spring force create a twisting moment that jams the brush into the commutator as rotation continues.

✅ Before You Answer

• Identify which figure clearly labels frictional force and shows its direction relative to rotation • Note where the spring tension is applied and how the brush is tilted compared with the radius line of the commutator • Verify that in your chosen option, the friction force would cause a wedging or jamming action of the brush into the commutator, characteristic of a reaction-type holder