Question

In an electric motor why only the brushes made up of carbon are used why not iron, copper etc.?

Answer 1

There are a number of reasons, including:
1. Carbon is self-lubricating.
2. Carbon has a negative temperature coefficient of resistance, which means that its resistance falls as its temperature increases -which is opposite that of metals such as copper.
3. Carbon is softer than copper, so will not damage the commutator.
4. Carbon will acquire the shape of the commutator segments and, so, will ensure maximum contact with them.