Electrical Machines
A commutator in DC machines can 1. provide half-wave rectification 2. Provide full-wave rectification 3. convert ac to dc 4. Convert dc to ac 5. provide controlled full-wave rectification From these, the correct answer is

 2, 3 ,5
 2, 3, 4
 1, 2, 3
 2, 3, 4, 5

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Electrical Machines
With the increase in speed of a DC motor

 back emf falls and line current increases.
 both back emf as well as line current increase.
 back emf increases but line current falls.
 both back emf as well as line current fall.

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