As the brushes ride on the commutator of a...

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Question 1 of 205eccefa3bacbc34ba4d480a5

As the brushes ride on the commutator of a DC generator, eventually mica ridges will form between the bars causing sparking and chipping of the brushes. When this happens the mica must be undercut. To what depth is the mica undercut?

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🔍 Key Concepts

• Function of mica insulation between commutator bars in a DC generator • Effect of brush wear and commutator surface on sparking • Mechanical limits: how deep you can safely cut without weakening the commutator bars

💭 Think About

• Think about why you undercut the mica in the first place: what problem are you trying to prevent as the brushes ride on the commutator? • If the undercut is too shallow, what will still happen to the brushes over time? If it is too deep, what could happen to the commutator mechanically? • Compare the slot depth to the slot width: which relationship would give a safe, effective recess without removing unnecessary material?

✅ Before You Answer

• Make sure the chosen depth gives a definite recess below the copper surface, so the brushes ride on copper, not mica. • Check whether the option would avoid excessive weakening of the commutator bars by cutting too deep. • Eliminate any choice that suggests the depth is “unimportant”, since maintenance procedures for rotating machinery are usually specified fairly precisely.

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