For a DC machine, in a commutator ________(a) Copper is harder than mica(b) Mica and copper are equally hard(c) Mica is harder than copper(d) Cannot be determinedThis question was addressed to me in homework.My question is taken from Commutation Process in division Commutation Process & Excitation Methods of DC Machines

For a DC machine, in a commutator ________(a) Copper is harder than mi

1.	For a DC machine, in a commutator ________(a) Copper is harder than mica(b) Mica and copper are equally hard(c) Mica is harder than copper(d) Cannot be determinedThis question was addressed to me in homework.My question is taken from Commutation Process in division Commutation Process & Excitation Methods of DC Machines
Answer» The CORRECT CHOICE is (c) Mica is harder than copper Explanation: Due to its MECHANICAL strength and insulating properties mica is a satisfactory material. However, mica is much harder than the copper SEGMENTS, so during manufacturing it requires to under-cut the mica by sawing slots between the adjacent segments of the commutator.

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