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Electrical Machines: 


Electrical Machines are the devices which convert mechanical energy into electrical energy and vice versa. It is also used to transform one form of electrical energy into another. Electrical Machine’s work on the principle of electromagnetic forces, which lead to either mechanical or electrical operations. These technologies find diverse applications in the field of power generation, green energy and electrical transmissions. 


Electrical Machines Sample Questions:


Question 1: An _______________ energy conversion device is one which converts electrical to mechanical and mechanical to electrical form of energy. 


a) electro-mechanical                       b) mechanical-electro

c) electrical                                       d) mechanical 


Answer: electro-mechanical

Explanation: The principle behind the conversion of mechanical to electrical and electrical



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Question 2: Short pitched coil ___________ the generated EMF in the system.


a) increases                  b) decreases 

c) either (a) or (b)          d) none of these

Answer: decreases 

Explanation: The effect of a short pitched coil



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Question 3: Which of the following losses is evaluated using  retardation test on DC shunt motor?


a) Iron losses               b) Copper losses 

c) Friction losses         d) Stray losses 

Answer: Stray losses 

Explanation: Retardation test is used to find stray



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Question 4: In the hopkinson’s test, Machine A has field current of 1.6A and B has field current of 1.4A. Which of the above machines acts as a motor?


a) A                                           b) B

c) Both (a) and (b)                    d) none of these

Answer: B

Explanation: Given, 


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Question 5: Which of the following is responsible for the change in terminal voltage, when the load on a generator is varied?


a) Armature reactance            b) Leakage reactance

c) Armature resistance           d) All of the above


Answer:  Armature resistance  

Explanation: Armature resistance generally causes reduction in air gap flux and, which further reduces



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Question 6: In terms of operation, which of the following is similar to an induction motor?

a) Stepper motor              b) Synchronous motor 

c) Universal motor            d) Transformer  

Answer: Transformer  

Explanation:  Induction motor has a similar operation as the transformer. It works on



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Question 7: An induction motor with 1500 rpm speed will have 


a) 2 Poles               b) 3 Poles

c) 4 Poles               d) 6 Poles


Answer:  2 Poles  

Explanation: n = Synchronous speed (rpm) , f = supply frequency (induction motor), p = pair of poles per phase



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Question 8: What is the effect on current, if the resistance of the field winding of the D.C. generator is increased?


a) Decreases                   b) Increases

b) Constant                     d) None of these 


Answer: Decreases

Explanation: If the resistance of the field winding is increased, current in the field decreases.



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Question 9: ____________ can be used for braking purposes in electric trains.


a) D.C Motor                        b) Induction Motor 

c) Induction generator          d) All of these    


Answer: Induction generator

Explanation: Induction generator runs at a very high speed, which is greater than the synchronous speed.  



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Question 10: Which of the following is used to maintain constant voltage at the end of the feeder?


a) Shunt Motor              b) Differential compound DC

c) Induction Motor          d) DC series generator 


Answer: DC series generator 

Explanation: In a DC series generator, end voltage increases as the load increases from no load to full load.



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