Wednesday, 9 April 2014

PEE SECOND MID UNIT WISE BITS

  UNIT-VIII: Single phase induction motors

Section-I: Multiple choice questions

1. At starting, the line current of a capacitor start induction motor is ______ the normal full load current[ b ]
(a)8 to 10 times (b)4 to 5 times (c) equal to (d)7 to 8 times

2.  The main winding and starting winding of a single phase induction motor are connected in__________ across the supply. []
(a)series (b) parallel (c)series parallel (d)none

3.  The main winding and starting winding of a single-phase induction motor are connected in ________ across the supply [b ]
(a) series (b) parallel (c) series-parallel (d) none of the above

4. The main winding and starting winding of a single-phase induction motor are connected in ________ across the supply [b ]
(a) series (b) parallel (c) series-parallel (d) none of the above

5.A two-phase a.c. servometer has [b ]
(a) wound rotor (b) cage rotor (c) wound or cage rotor (d) a rotor similar to that in d.c motors
Section-II: Fill in the blanks

1. In capacitor start induction motor the angle between Im and Is is about  75˚

2. The purpose of starting winding in a single phase induction motor is to produce rotating flux
3. A single phase induction motor employs squirrel cage rotor

4. A 50 Hz, 4-pole, single-phase induction motor will have a synchronous speed of 1500 RPM
5. The full-load efficiency of a shaded-pole motor is about 30 to 35 %.
6. The amount of torque required to move a stepper motor one full step is called   holding torque


                                 


 UNIT-5:   D.C. Generators

 1. The type of compound generator commonly used for obtaining an almost constant terminal voltage is    [   b   ]
(a) Over compound (b)flat compound (c)cumulative compound (d)under compound 
2. In a DC machine, the number of Commutator segments is equal to [ c ]
(a)number of conductors (b)number of poles (c)number of coils (d)both a and b

3.  The yoke of a dc machine is made up of    [  d  ]
(a) silicon steel (b)soft iron (c)aluminium (d)cast steel

4. The field winding of a d.c shunt machine usually carries ______ of the rated current of the machine [ ]
(a) 2% to 5% (b) 15% to 20% (c) more than 20% (d) less than 0.5%

5.A shunt generator delivers 195 A at a terminal p.d of 250 V. The armature resistance and shunt field resistance are 0.02Ω and 50Ω respectively. What is the value of generated e.m.f?c ]
(a) 246 V (b) 270 V (c) 254 V (d) 282 V

6. In a long-shunt compound-wound generator, the shunt field is connected parallel with
 [ d  ]
(a) armature (b) parallel combination of armature and series field
(c) series field (d) series combination of armature and series field

7. The Commutator in a dc machine can be convertc]
(a) ac to dc (b) dc to ac (c) both a and b (d) None of the above

8.The emf produced in the dc generator is ____ induced emf [ b ]
(a) Statically (b) Dynamically (c) magnetically (d) Electrostatically

9.  DC generator operates on the principle ofa]
(a) Electromagnetic induction (b) Lenz's law (c) Biov Savart's law (d) none of these

10. The Mechanical energy source used to drive a dc generator is called a [ b  ]
(A) Rotor (B) Prime Mover (C) Alternator (D) Motor drive

11.  The nature of current having in the armature of a dc machine is _____ [ a ]
a) AC b) DC c) pulsating d) None

12.  The induced voltage in a single loop reverses_____b ]
a) Once each revolution b) once each half revolution
c) one each quarter revolution d) 8 times each revolution
13.  The field of self excited generator is excited by [   c]
a) Dc b) Ac c) By its own current d) Either ac or Dc

14.  Emf induced in each conductor of a DC Machine is [ a ]
A) An alternating emf B) A direct emf
C) A pulsating emf D) Emf of random wave shape

15.  The residual magnetism of a DC shunt generator can be regained by [a ]
A) Connecting the shunt field to a battery B) Running the generator on no load for sometime C) Grounding the shunt field D) Reversing the direction of rotation of the generator.

16.  A DC Generator working is based on the principle of [ c]
(A) Ohm’s Law (B)Statically induced emf
(C)Dynamically induced emf (D) Mutual induction

17.  D.C. generator generates [b ]
a) D.C. voltage in the armature b) A.C. voltage in the armature terminals
c) A.C. super imposed over d.c. d) None of above

18.  E.m.f generated in the armature terminals of a d.c. generator is [d ]
a) Directly proportional to number of poles b) Directly proportional to the flux per pole
c) Directly proportional to number of conductors per path d) All (a), (b) and (c)


19.  The generator develops electric pressure by (c )
A. Conversion of heat B. Conversion of light
C. Electro-magnetic induction D. Conversion of Chemical energy

20.  In separately excited D.C generator the field is connected (c )
A.In series with armature B. Across the armature C. To an external source D. None

21.  Slip rings are usually made of (b )
A. copper B. carbon C. phosphor bronze D. aluminum

22.  An electric _________ is a machine which converts mechanical energy (or power) is to electrical energy (or power) [ d]
A) Motor B) Induction Motor C) Synchronous Motor D) Generator
23.  The Mechanical energy source used to deive a dc generator is called a [b ]
(A) Rotor (B)Prime Mover (C) Alternator (D) Motor drive

24.  In a multi polar (P-pole) machine running at a speed of N rpm, the frequency of generated emf is given as _______ [d ]
a) f=pn/60 b) f=pn c) f=n/p d) f=np/120

25.  The field of self excited generator is excited by [ c]
a) Dc b) Ac c) By its own current d) Either ac or Dc


26.  Generator converts [a ]
a) mechanical energy to electric energy b) electric energy to mechanical energy c) both d) none

27.  In a DC machine the iron losses are also called as [a ]
a) core losses b) eddy current losses c) hystersis losses d) all the above

28.  The armature current in a DC machine is collected by [ b]
a) Yoke b) brushes c) poles d) all the above

29. The Armature core of a de machine is made up of ( d)
(a) Solid Aluminum (b) Laminated Aluminum (c) Solid steel (d) Laminated steel
30. Which type core coupling occurs between a mechanical and Electrical System ( b)
(a) Electrostatic (b) Electro mechanical (c ) Mechanical (d) Electrical
31.  The highest speed of a 50 Hz AC generator can be [b ]
A) 6000 rpm B) 3000 rpm C) 1500 rpm D) 7000 rpm
32.  High permeability magnetic materials helps [ a]
A) To confine the flux within the magnetic circuit. B) To allow the flux to leak C) In producing more current. D) None of these
33.  For iron the curve between flux linkages () and current (i) is______ [ b]
a) Linear b) Non-linear but not circle c) circle d) semi-circle
34.  The greatest percentage of heat loss in a d.c. machine is due to____ [ d]
a) Eddy current loss b) Hysteresis loss c) frictional loss d) copper loss
35.  The field winding of a d.c.shunt machine usually carries____ __of the rated current if the machine [a ]
a) 2% to 5% b)15% to 20% c) more than 20% d) less than 0.5%
36.  In a dc generator, the generated EMF is directly proportional to the [b ]
a)Field current (b) pole flux (c) parallel paths (d)no. of dummy coils

37.  Faradays ________ law states that the magnitude of induced emf is equal to the rate of change of flux linkages. [b ]
A)First B) Second C) Third D) Fourth

38.  The material for commutator brushes is generally [d ]
A)Mica B) Copper C) Cast Iron D) Carbon

39.  In DC generators, lap winding is used for [ b]
A)High voltage, high current B) Low voltage, high current
C) High voltage, low current D) Low voltage, low current

40.  In a shunt generator the voltage build up is generally restricted by
[d ]
A) Speed Limitation B) Armature heating
C) Insulation Restrictions D) Saturation of Iron

41.  In a DC generator the critical resistance refers to the resistance of
 [ b]
A) Brushes B) Field C) Armature D) Load

42. A dc generator is machine that converts [ c]
A)Electrical to mechanical (B) chemical to electrical
(C)Mechanical to Electrical (D) none of the above

43. In a dc generator the emf is induced in the [B ]
(A) field coils (B) Armature coils (C) commutator segments (D)brushes

44.  The function of the brushes in a DC generator is to [ A]
(A) carry current to external circuit (B) prevent sparking
(C) keep the commutator clean (D) convert AC into DC

45.  The voltage of a DC Shunt generator is built up by [C ]
(A) permanent magnetism (B) proper operation of the field rheostat
(C) residual magnetism (D) increasing the speed

46.  Which of the following is not a part of the DC machine [ D]
(A) armature (B) commutator (C) field winding (D) damper winding

47.  Stray losses in a DC generator consist of _____ losses [A]
(A) Magnetic and Mechanical Losses (B) Magnetic and Electrical losses
(C) Copper and Iron Losses (D) None of the above





48. Which of the following is a function of the yoke [c ]
A) To reduce eddy current loss B) To support the field winding
C) To provide a return path for the flux D) To distribute the flux uniformly

49. A dc series generator has a terminal voltage of 110V. The armature resistance is 0.2 ohms and current is 10A. The generated emf is _____________ volts. [A ]
A) 112 B) 115 C) 120 D) 125

50. In a DC generator, the initial voltage is produced due to [B ]
A) Saturation of the core B) Residual magnetism
C) Eddy currents D) Hysteresis

51. A 6-pole lap-winding generator has 300 conductors the emf induced per conductor being 5V. The generated voltage of the generator is [ ]
A) 60V B) 1500V C) 360V D) 250V

52. A dc shunt generator gives its greatest voltage at [A ]
A) No load B) Full load C) Half full load D) None of the above

53. the maximum eddy current loss occur in _________ of a dc machine [ c]
A) Field poles B) Yoke C) Armature D ) Commutating poles

54. The efficiency of a dc generator means [ D]
A) Electrical efficiency B) Mechanical efficiency C) Overall efficiency D) None
55. The terminal voltage of the __________ generator widely changes in load current [ A]
A) Series B) Shunt C) Flat compounded D) Over compounded

56. The running speed of the dc series motor is basically determined by
[ B]
A) Field excitation B) Load C) Armature resistance D) None

Section -II
1. The brushes that carry the current to the load are made up of   Carbon
2. Power lost as heat in the armature and field windings of a dc machine is called COPPER loss.
3. A shunt generator delivers 195A at a terminal p.d of 250V. The Ra and Rf are 0.02Ω and 50Ω respectively. The generated emf is 254V
4. In a cumulatively compounded generator, the shunt and series fields aid each other
5. The e.m.f equation of a d.c generator in terms of flux, poles etc is given by Eg = (ΦZNP) / (60 * A)
6.  The most economical method of finding no-load losses of a large d.c. machine is  Swinburne’s test.
7. Emf equation of generator is  Eg = (ΦZNP) / (60 * A)
8. Yoke is made of which material   Cast iron or Cast steel
9. Types of windings in dc generator   Lap winding ,wave winding
10. The magnetic field which initially induces emf in the armature in a self excited dc generator is Because of Residual magnetism(residual flux)

11. Faraday's second Law states that the magnitude of individual emf is equal to the rate of  Change of flux linkages.
12.A four pole DC generator is running at 1500 rpm. The frequency of current in the armature is 50Hz
13. The armature of a dc machine is a laminated to reduce Eddy current losses

14. The function of interpoles in a dc machine is to   improve commutation
15. The EMF induced in a coil rotating in a uniform magnetic field is maximum when the flux linkage by the coil is  minimum
16. The O.C.C of a d.c. generator is also called its magnetic or no load saturation characteristic.
17. The number of parallel paths are equal to number of poles when Armature conductors are connected in  Lap winding
18. In d.c. generators, current to external circuit from armature is given through Commutator
19. Main purpose of carbon brushes in a d.c. machine to improve the commutation process
20. The e.m.f produced in a D.C generator is Dynamically induced e.m.f
                           
21. The armature current and field current will be equal in case of a D.C series machine
22. Whenever a conductor cuts magnetic flux, dynamically induced emf is produced in it according to Faradays law of  Electromagnetic induction
23.LAP winding in DC machine is used for low voltage, high current generators
24. Slip rings are usually made of  Phosphor Bronze  material
25. An AC generator having 6 poles is required to generate voltage at 120 cps, The speed of the generator is ______________rpm

26. The greatest eddy current loss occurs in the Armature of a d.c. machine.
27. A d.c. compound generator having full load terminal voltage equal to the no-load voltage is called  Flat-compounded generator
28. Lap winding is suitable for high   current but  low voltage generators
29. In lap winding, the number of brushes is always  no. of poles
30. The armature core of a DC generator is usually made of  Silicon Steel
31. In over compound generator, full load terminal voltage is  More than no-load terminal voltage
32. The law of working principle of DC generators is Fleming’s right hand rule

33. When constant terminal voltage is required at the output terminals, shunt types of DC generator is used.

34. In a Long shunt compound generator, the shunt field is connected in parallel with series combination of armature and series field

35. If the flux per pole of a DC Generator is halved but its speed is doubled, the generated emf will be remains same
____________________


36. To raise generator voltage, we have to  raise the field current

37. An application of a differential compound generator is Arc welding

38. Wave winding is suitable for______________current but ________________voltage generators

39. A dc generator beyond critical resistance wills generate  No emf
40. The rotating part of a DC machine is   Armature

41.


                                



                                            UNIT-6:D.C.MOTORS

1.  In a DC machine, the number of commutator segments is equal to [c ]
(a)number of conductors (b)number of poles (c)number of coils (d)both a and b

2.  Main advantage of differentially compound motor is that    [ ]
(a)stable under heavy loads (b)speed increases to very high values on no load
(c)speed remains constant if load is not excessive (d)start under heavy load

3.  Which of the following motor should never be started on no load     [  d ]
(a)shunt (b)compound cumulative (c)compound differentially (d) series

4.  The yoke of a dc machine is made up of [  d ]
(a)silicon steel (b)soft iron (c)aluminium (d)cast steel

5.  The value of back emf in a dc motor is maximum at _______ [ ]
(a)no load (b)full load (c)half full load (d)one fourth full load

6.  The field winding of a d.c shunt machine usually carries ______ of the rated current of the machine [  a]
(a) 2% to 5% (b) 15% to 20% (c) more than 20% (d) less than 0.5%

7.  The speed of a d.c. motor can be controlled by changing [   ]
(a) its flux (b) armature circuit resistance
(c) applied voltage (d) all of the above

8. By putting controller resistance in series with the armature of a d.c motor, we can obtain speeds [ b]
(a) above the normal speed only (b) below the normal speed only
(c) above as well as below the normal speed (d) none of the above

9 . The only disadvantage of field control method for controlling the speed of a d.c shunt motor is that it [  c]
(a) give speeds lower than the normal speed (b) is wasteful
(c) needs a large rheostat (d) adversely affects commutation

10.  The Commutator in a dc machine can be convert [ c]
(a) ac to dc (b) dc to ac (c) both a and b (d) None of the above

11.  Fleming's left hand rule is applicable for: [b ]
(a) dc generator (b) dc motor (c) alternator (d) Transformer

12. The armature torque of the dc shunt motor is proportional to []
(a) armature current only (b) field flux only (c) armature current and flux both (d) None

13.  Motor which should not run at no-load is [a ]
(a) Series motor (b) shunt motor (c) compound motor (d) induction motor

14.  High permeability magnetic materials helps [a ]
A) To confine the flux within the magnetic circuit. B) To allow the flux to leak
C) In producing more current. D) None of the

15.  A Commutator in a DC machine can convert ____ to ______ [ c]
(a) AC, DC (b) DC, AC (c) either ‘A’ or ‘B’ (d) None

16.  The current flowing through armature conductors of a dc motor is _____________ [c ]
a) Pulsating b) Dc c) Ac d) none of these


17  In Swinburne’s test of a Dc machine [ b]
a) No load losses are calculated and copper losses are measured
b) No load losses are measured and copper losses are calculated
c) Both the losses are measured
d) Both the losses are calculated

18.  The supply terminals for a dc shunt motor are reversed. What will be effect on the motor [b ]
a) It will run as Dc generator b) runs in reverse direction c)it stops d)its burns

19.  The magnitude of force acting on a current carrying conductor placed in a magnetic field is independent of [ c ]
A) Flux density B) length of conductor
C) cross-sectional area of conductor D) current flowing Through the conductor



20.  When a dc machine is connected in the dc supply main it will produce [ d]
A) Emf in opposition to applied voltage. B) Unidirectional torque
C) Copper losses in the windings D) all of the above

21.  Emf induced in each conductor of a DC Machine is [a ]
A) An alternating emf B) A direct emf
C) A pulsating emf D) Emf of random waveshape

22.  The starting torque of a dc shunt motor is [b ]
A) Zero B) low C) high D) very high

23.  The eddy current losses is directly proportional to [ b ]
a) f b)f^2 c)f^1.6 d)f^3

24.  The iron losses [ d]
a) core losses b) eddycurrent losses c) hystersis losses d) all the above

25.  The speed of a d.c motor can be controlled by varying [d ]
a)its flux per pole b)resistance of armature circuit c)applied voltage d)all the above

26.  The Swinburne’s test in a DC machine is also called as [a ]
a) no-load test b) Full-load test c) half-load test d) 1/3-load test

27.  Series motor is used for………………applications [d ]
a) constant speed b) constant torque c) high starting speed d) high starting torque

28.  3-point starter in DC motor is used to limit [a ]
a) current b) voltage c) both a and b d) none

29.  Application of DC shunt motor is [a]
a) For driving machine tools b) For driving cranes
c) For driving Hoists d) For driving Trains

30.  Torque developed by a DC motor depends upon [ d]
a) Current flow through conductors b) Magnetic field and active length of the conductors
c) Number of conductors and radius of armature d) All the above factors

31.  A series motor has a relatively [ a]
a) High starting torque b) Medium starting torque
c) Low starting torque d) a zero starting torque

32. Fleming’s left hand rule is applicable to ( b)
A. DC generator B. DC motor C. Alternator D. Transformer

33.  The current flowing through armature conductors of a dc motor is _____________ [ c]
a) Pulsating b) Dc c) Ac d) none of these

34.  In a DC motor Swinburne’s test is also called as [ c]
a) half load test b) full-load test c) no-load test d) all

35.  For constant speed applications which DC motor is preferred [ b]
a) Series b) shunt c) compound d) all

36.  The torque developed in DC motor is based on ……………… [ a]
a) Lenz’s law b) faraday’s law c) gauss’s law d) All

37. The output of a dc motor depends mainly on the following two factors [ D]
A)Speed and applied voltage (B) Speed and back emf.
(C)Torque and applied voltage (D) Speed and torque

38. The formula for the torque developed by a dc motor is [ A]
(A)T=K.Iaφ (B) T=K2Ia2φ (C) T=Kia 2Φ2 (D) T=KIa / φ

39. The direction and force can in the DC motor determined by [ c]
A)Fleming’s Right hand rule (B) Lenz’s law
(C)Fleming’s Left hand rule (D) Ohm’s law

40.  The armature current drawn by a DC motor is given by Ia = V/Ra only when [ A]
(A) its stationery (B) runs at half load (C) runs at full load (D) None

41.  The armature power developed by a DC motor is given by [ B]
(A) VIa (B) EbIa (C) Ia2Ra (D) All the above

42. The direction of torque in a DC motor is determined by [D ]

A) Faraday’s laws of electromagnetic induction B) Ohm’s Law
C) Fleming’s right hand rule D) Fleming’s left hand rule

43. Which of the following is true, representing the mechanical characteristics of a DC Shunt motor [ A ]
A) Speed versus torque B) Terminal voltage versus filed current
C) Generated emf versus field current D) Terminal voltage versus load current

44. The back e.m.f in a d.c motor [A ]
A) Opposes the applied voltage B) Aids the armature current
C) Aids the applied voltage D) None of the above
45. The Armature core of a de machine is made up of [ d  ]
(a) Solid Aluminum (b) Laminated Aluminum (c) Solid Steel(d) Laminated Steel

46. Which type core coupling occurs between a mechanical and Electrical System [b ]
(a) Electrostatic (b) Electro mechanical (c ) Mechanical (d) Electrical

47. The direction of rotation of a dc motor can be determined by________________ [  B ]
A) Fleming's right hand rule B) Fleming's left hand rule
C) Lenz's law D) Ampere's la

48. A dc series motor must not be started on no-load because it would [ A ]

A) Run at dangerous speed B) Zero speed
C) Runs rated speed D) Run half of rated speed

49. Motor starters are essential for [ D  ]

A) Accelerating the motor B) Starting the motor
C) Prevent fuse blowing D) Avoiding excessive starting current

50. The resistance of the shunt field winding as compared to the series field winding [  B ]
A) Less B) More C) Same D) None


51.  A d.c series motor is most suitable for [  D]
A) Punch presses B) Pump C) Laths D) Cranes

52. A brake test is usually restricted to ______________ dc motors [ A ]
A) Small kw output rating B) Variable speed C) High speed D) Constant speed


                        SECTION-II:FILL IN THE BLANKS

1. The brushes that carry the current to the load are made up of Carbon
2. Power lost as heat in the armature and field windings of a dc machine is called  copper loss
3. Series dc motor should never be started on no load.
4. The relation between speed, flux and backemf in a dc motor is   NαEb/Ф
5. The motor terminal voltage equation is given by  V = Eb+ IaRa
6. The most economical method of finding no-load losses of a large d.c. machine is swinburne’s test.
7. Yoke is made of which material Cast iron or Cast steel
8. Losses in DC machine are Iron losses,Cu losses, Mechanical losses
9. Types of     DC motors , D.C series motor, d.c shunt motor
10. In DC shunt motor the Torque is directly proportional to Ia
11. The starting resistance for a dc shunt motor  Low
12. A 3 point starter is considered suitable for dc Shunt motor
13. The armature of a dc machine is a laminated to reduce  Eddy current losses
14. If the flux of a dc motor approaches zero its speed will Infinite
15. The direction of mechanical force experienced on a current carrying conductor placed in a magnetic Field is determined by Fleming’s left hand rule
16. The function of interpoles in a dc machine is to improve commutation

17. The speed of a DC motor is directly proportional to its Back emf and inversely proportional To Flux
18. The current drawn by a dc motor at the starting instant will be High
19. The collection of current from armature conductors to the external load is the function of Commutator and brushes
20. The iron or core losses are also known as Constant losses
21. In d.c motor unidirectional torque is produced with the help of-Brushes-and commutator.
22. Under constant load conditions, the speed of a d.c motor is affected by V, Ra, Ø
23. The Eb/V ratio of a d.c motor known as Efficiency
24. An invertor is employed to convert DC voltage to AC voltage
25. When load is removed,D.C.series motor will run at the highest speed.
26. The purpose of starter for DC Motor is to control the starting current
27. The condition for maximum efficiency is when constant losses are equal to variable losses
28. The DC shunt motor is used for constant  speed  applications
29. Three point starters are used for starting of both shunt and compound motor
30. The speed of a DC motor is directly proportional to its EMF and inversely proportional to FLUX
31. The predetermination of efficiency of a DC motor is done by the Swinburne’s test


32. The speeds above the rated speed in a DC machine can be obtained by field flux control method.
33. Induced EMF equation of a DC machine is  E= (ΦZNP)/ (60*A)
34. The interaction between the Armature flux and the flux produced by the rotor direct correct is  Armature Reaction
35.  The type of DC motor that can be used for applications involving nearly constant speed is
D.C. Shunt motor
36. The armature speed control method provides the speed control Below the rated speed.
37. Condition for maximum torque developed by a DC motor is Eb = V/2
38. Because of its high starting torque, a series motor   is used for traction applications
39. The DC motor used for traction purpose is D.C.series motor
40. The condition for maximum efficiency in a DC machine is  Constant loss=variable loss
41. A 4-pole d.c. machine has   four  magnetic circuits

42. The motor equation is V=Eb+IaRa

43. The carbon brushes are preferable to copper brushes  because    reduce sparking
44. The speed of a   Shunt   motor  is practically constant

45.The interaction between the Armature flux and the flux produced by the rotor direct correct is   Armature reaction

46. The Armature core of a dc machine is made up of Laminated Steel

47. If the back emf in a dc motor vanishes suddenly, the motor will Burn

48. Shunt motor has the best speed regulation

49. The terminal voltage equation for the motor is V = Eb + I a Ra
50. The armature current and field current are equal in the case of Series and over compound  machines
51. The armature reaction is given by The effect of armature flux on distribution of main field flux.
52. The starting torque of the dc shunt motor is  Low
53. The current drawn by the dc motor at starting is Very high
54. A 3 point starter is suitable for shunt motors
55. The variable losses in the dc shunt machine is Armature copper losses










                                             UNIT-7: TRANSFORMERS

           SECTION-1: MULTIPLE CHOICE QUESTIONS

1. A Transformer will have low efficiency at ________________Load [C   ] 
 A) Full load B) Half load C) No-load D) none

2. A transformer has an efficiency of 80% and works at 100V, 4KW. If the secondary voltage is 240V, find primary current [a ]
(a)40A (b)30A (c)20A (d)10A

3.The no load current of a transformer is generally of the order of _______the full load current []
(a)less than 5% (b)more than 5% (c)equal to that (d)zero

4.  The open-circuit test on a transformer is always made on [ a]
(a) low-voltage winding (b) high-voltage winding
(c) Either low or high voltage winding (d) none of the above

5. The Principle of operation of a Transformer is  [  B]
(A) Electromagnetic Induction (B)Mutual Induction
(C) Varying a conductor in a magnetic field (D) Electrostatic induction

6.  The flux involved in the emf equation of a transformer has [   D]
(A) RMS value (B) Average value (C) Total value (D) Max. value

7.  In a single phase transformer, with subscripts 1 and 2 for primary and secondary windings[a ]
(A) E1N2= E2N1 and I1N1= I2N2 (B) E1N1= E2N2 and I1N1= I2N2
(C) E1N2= E2N1 and I1N2= I2N1 (D) E1N1= E2N2 and I1N2= I2N1s

8.Eddy current losses in a transformer core can be reduced by _____ [ a ]
(a) Reducing the thickness (b) decreasing air gap in the magnetic circuit
(c) Increasing air gap in the magnetic circuit. (d) Increasing the thickness

9. Which of the following describes a transformer [b ]
(a) Mechanical device (b) Static device (c) Electrostatic device (d) Rotating device

10. A Step up Transformer is step up level of _______________ [A ]
A) Voltage B) Current C) Power D) Frequency

11. Transfer of electrical power from primary to secondary in a transformer takes place [B]
A) Electrically B) Electromagnetically
C) Magnetically D) None of these


12. The short circuit test of a transformer gives the information of [A ]
A) Cu losses of the transformer B) Core losses of the transformer
C) Winding circuit impedance D) None of these

      SECTION 2: fill in the blanks

1.The iron core in a transformer provides a LOW RELUCTANCE path to the main flux.

2. The type of value of flux involved in the emf equation for a transformer is MAXIMUM

3. The transformation ratio of a transformer is   N1/ N2

4. The primary ampere turns of transformer is EQUAL to secondary ampere turns.

5. The phasor postion of magnetizing current component of an ideal transformer in phasor diagram  lags the applied voltage by 900

6. If rated Dc voltage is applied instead of AC to the primary of a transformer thenprimary winding of the transformer will burn.

7. If Pi be the iron losses and Pc be the copper losses on full load, then the condition for obtaining the maximum efficiency at 3/4th full load is  
Pc= (16/9) Pi

8.A transformer can have Zero regulation at leading power factor.

9. The chemical used in breather is silica gel

10. the no load current in a transformer lags the applied voltage by  75˚

11. In a Transformer Core is laminated to reduce    Eddy current loss

12. Condition for maximum efficiency of Transformer is Constant losses = variablelosses

13. THE efficiency of transformer is ______________

14. The shot circuit test is conducted to determine is COPPER LOSSES AND  SERIES PARAMETERS

15. The core losses in a transformer consists of Hysteresis and Eddy current losses

16. The voltage regulation of a transformer can be determined by conducting Open Circuit (OC) and Short Circuit (SC) tests.

17.  The open-circuit test on a transformer gives Iron losses

18. A transformer has full-load copper loss of 400 W. The copper loss at half-full load will be 100W

19. Transformer operates on AC only.

20 A transformer steps up the voltage by a factor 100. The ratio of current in the primary to that in secondary is 100

21. Efficiency of a transformer is maximum if  Iron losses=cu losses

22.  The Regulation of a Transformer is zero, when the Power factor is leading

23. The shot circuit test is conducted to determine is Series parameters

24. In a Transformer Core is laminated to reduce Eddy current losses

25. The no load current in a transformer lags the applied voltage by approximately 90˚










                                  UNIT-VIII: Single phase induction motors

Section-I: Multiple choice questions

1. At starting, the line current of a capacitor start induction motor is ______ the normal full load current[ b ]
(a)8 to 10 times (b)4 to 5 times (c) equal to (d)7 to 8 times

2.  The main winding and starting winding of a single phase induction motor are connected in__________ across the supply. []
(a)series (b) parallel (c)series parallel (d)none

3.  The main winding and starting winding of a single-phase induction motor are connected in ________ across the supply [b ]
(a) series (b) parallel (c) series-parallel (d) none of the above

4. The main winding and starting winding of a single-phase induction motor are connected in ________ across the supply [b ]
(a) series (b) parallel (c) series-parallel (d) none of the above

5.A two-phase a.c. servometer has [b ]
(a) wound rotor (b) cage rotor (c) wound or cage rotor (d) a rotor similar to that in d.c motors
Section-II: Fill in the blanks

1. In capacitor start induction motor the angle between Im and Is is about  75˚

2. The purpose of starting winding in a single phase induction motor is to produce rotating flux
3. A single phase induction motor employs squirrel cage rotor

4. A 50 Hz, 4-pole, single-phase induction motor will have a synchronous speed of 1500 RPM
5. The full-load efficiency of a shaded-pole motor is about 30 to 35 %.
6. The amount of torque required to move a stepper motor one full step is called   holding torque