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, 4, 5
 2, 3 ,5
 2, 3, 4
 1, 2, 3

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Electrical Machines
A DC shunt generator builds up to a voltage of 220 V at no load while running at its rated speed. If the speed of the generator is raised by 25% kepping the circuit conditions unaltered, then the Voltage to which the machine would build up will

 increase to 1.25 times 220 V
 not change and remain at 220 V
 increase to value lying between 220 V and 1.25 times 220 V
 increase to a value greater than 1.25 times 220 V

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