Class: XII
Electrical Machines-(787)
Sample Question Paper 2019-20

SECTION–A

Answer any 10 questions out of the given 12 questions:
1. Which motor cannot be started on no load?
(a) Series Motor
(b) Shunt motor
(c) Cumulative compound motor
(d) Both b and c.
 
2. Which of the following motor has negative speed regulation?
(a) Seriesmotor
(b) Stunt motor
(c) Cumulative compoundmotor
(d) Differential compoundmotor
 
3. Core of transformer is laminated to
(a) Reduce hysteresislosses
(b) Eddy currentlosses
(c) Copperlosses
(d) All of theabove
 
4. A transformertransforms
(a) Power factor
(b) Voltage
(c) Power
(d) Energy

5. Natural oil cooling is used in transformer upto a rating of
(a) 3000 kVA
(b) 1000 kVA
(c) 500 kVA
(d) 250 kVA
 
6. Soldering iron is made of wedge shape in order to......
(a) Apply high pressure atedge
(b) Retainheat
(c) Retainsolder
(d) Forge welding
 
7. The purpose of using flux in soldering is to.......
(a) Increase fluidity of soldermetal
(b) Feel up gaps left in a badjoint
(c) Carbonsteel
(d) Prevent oxidesforming
 
8. The starting torque of a capacitor start motor is
(a) zero
(b) low
(c) same as ratedtorque
(d) more than ratedtorque.
 
9. A universal motor is one
(a) which can run on any value of supplyvoltage
(b) which has infinitely varyingspeed
(c) which can operate on ac as well as dc voltage
(d) which can work as single phase or three phasemotor.
 
10. The motor used in household refrigerators is
(a) dc seriesmotor
(b) dc shuntmotor
(c) universalmotor
(d) single phase inductionmotor.
 
11. The direction of rotation of universal motor can be reversed by
(a) reversing the supplyterminals
(b) switching over from ac todc
(c) interchanging the brushleads
(d) any of theabove.
 
12. In an induction motor, rotor speed is always
(a) Less than the statorspeed
(b) More than the statorspeed
(c) Equal to the statorspeed
(d) None ofthese
 
Very Short Questions: (2 marks each).
Answer any 5 questions out of the given 7 questions:
13. How is speed control of dc motor achieved?  
14. What are the functions of poles in dc motors?  
15. What are characteristics of capacitor start motor?  
16. What are different types of solder?  
17. Give winding details of fractional horse power motor?  
18. What are the causes of faults in ac motor?  
19. List applications of voltage and current transformer.  

Short Questions: (3 marks each).
Answer any 5 questions out of the given 7 questions:
20. What is single phase repulsion motor? Also write various applications of single phase motor?
21. Describe the construction of starters used to start a three-phase slip-ring induction motor.  
22. Explain the construction and working principle of compound motor with a neat schematic diagram.
23. Explain testing, fault finding and repairing of dc motor.  
24. Describe working principle of Shunt motor. Also give the differences between series and shunt motor.
25. Draw and explain step up and step down transformers.  
26. Give construction details and winding details of shaded pole motor.  

SECTION –B

Long/Essay type questions (5 marks each).
Answer any 1 question out of the given 2questions:
27. What are various soldering techniques? Explain in details. 
28. Classify AC motors. Explain principle of operation, construction and characteristics of Universal Motor.

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