01․ A DC Shunt Motor having shunt field resistance of 250 Ω and armature resistance of 0.5 Ω is connected to 250 V supply and load current of 21 A. What is the back emf generated ?

02․ The flux is maximum in the following part of a DC motor:

In DC motor, flux is maximum under the trailing pole tip as the resultant flux is strengthened at the leading pole and weakened at the trailing pole tips due to armature reaction.

03․ In a loaded DC generator, if the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will

In order to reduce the adverse effects of armature reaction in DC machines, we should shift the brushes along the direction of rotation in generator and against the direction of rotation in motor. This would result in a reduction in air gap flux which will reduce the induced voltage in generator and would increase the speed in motor.

04․ What is the emf generated by a 4 pole Lap connected DC Motor rotating at 1500 rpm having 1000 conductors and useful flux per pole is 0.4 mWb.

05․ In a loaded DC motor, if the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will

In order to reduce the adverse effects of armature reaction in DC machines, we should shift the brushes along the direction of rotation in generator and against the direction of rotation in motor. This would result in a reduction in air gap flux which will reduce the induced voltage in generator and would increase the speed in motor.

06․ For a DC Shunt Motor having armature resistance of 0.5 Ω and 2 A armature current at no-load, when the armature current is changed to 20 A at loaded condition the speed is 1000 r.p.m. What is the speed at no-load?

07․ A DC motor with armature resistance of 0.5 ohms connected directly to a 220 Volt supply. If the armature is stationary then the current flowing through the armature is

As the armature is stationary so the back e.m.f E

_{b}is zero.08․ A DC compound motor has

In compound motor having both series and shunt field winding that is why it is called compound motor. It may be a short shunt compound or long shunt compound motor or it may be cumulatatively or differentially compounded depending upon the connection.

09․ In a DC Shunt Motor if the load current increases then field flux

In shunt motor, the field flux mainly depends upon field current. I

_{sh}= V_{t }/ R_{sh}, if V_{t}is constant then I_{sh}will also be constant. Hence the flux remains constant.10․ In DC series motor the speed is ______________ proportional to the armature current.

In DC series motor, the series field and armature field are carrying the same current, so the flux φ is produced by the armature current flowing in the field winding and φ is directly proportional to armature current Ia. From emf equation, it can be stated that N is inversely proportional to the flux and so in this case N is inversely proportional to armature current.

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