Three phase induction motor mcq part - 3

1. The power factor of an induction motor under no-load conditions will be closer to
(a) 0.2 lagging
(b) 0.2 leading
(c) 0.5 leading
(d) unity

Ans: a

2. The 'cogging' of an induction motor can be avoided by
(a) proper ventilation
(b) using DOL starter
(c) auto-transformer starter
(d) having number of rotor slots more or less than the number of stator slots (not equal

Ans: d

3. If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as
(a) humming
(b) hunting
(c) crawling
(d) cogging

Ans: c

4. Slip of an induction motor is negative when
(a) magnetic field and rotor rotate in opposite direction
(b) rotor speed is less than the syn-chronous speed of the field and are in the same direction
(c) rotor speed is more than the syn-chronous speed of the field and are in the same direction
(d) none of the above

Ans: c

5. Size of a high speed motor as compared to low speed motorfor the same H.P. will be
(a) bigger
(b) smaller
(c) same
(d) any of the abov

Ans: b

6. A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor
(a) will continue running burning its one phase
(b) will continue running burning its two phases
(c) will stop and carry heavy current causing permanent damage to its winding
(d) will continue running without any harm to the winding

Ans: a

7. A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the
motor
(a) will continue running burning its one phase
(b) will continue running burning its two phase
(c) will stop and carry heavy current causing permanent damage to its winding
(d) will continue running without any harm to the winding

Ans: c

8. Low voltage at motor terminals is due to
(a) inadequate motor wiring
(b) poorely regulated power supply
(c) any one of the above
(d) none of the above

Ans: c

9. In an induction motor the relationship between stator slots and rotor slots is that
(a) stator slots are equal to rotor slots
(b) stator slots are exact multiple of rotor slots
(c) stator slots are not exact multiple of rotor slots
(d) none of the above

Ans: c

10. Slip ring motor is recommended where
(a) speed control is required
(6) frequent starting, stopping and reversing is required
(c) high starting torque is needed
(d) all above features are required

Ans: d

11. As load on an induction motor goes on increasing
(a) its power factor goes on decreasing
(b) its power factor remains constant
(c) its power factor goes on increasing even after full load
(d) its power factor goes on increasing upto full load and then it falls again

Ans: d

12. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
(a) in the opposite direction as the direction of the rotating field
(b) in the same direction as the direction of the field
(c) in any direction depending upon phase squence of supply

Ans: b

13. It is advisable to avoid line starting of induction motor and use starter because
(a) it will run in reverse direction
(b) it will pick up very high speed and may go out of step
(c) motor takes five to seven times its fullload current
(d) starting torque is very hig

Ans: c

14. The speed characteristics of an induction motor closely resemble the speedload characteristics of which of the
following machines
(a) D.C. series motor
(b) D.C. shunt motor
(c) universal motor
(d) none of the above

Ans: b

15. Which type of bearing is provided in small induction motors to support the rotor shaft
?
(a) Ball bearings
(b) Cast iron bearings
(c) Bush bearings
(d) None of the above

Ans: a

16. A pump induction motor is switched on to a supply 30% lower than its rated voltage.
The pump runs. What will eventually happen ? It will
(a) stall after sometime
(b) stall immediately
(c) continue to run at lower speed without damage
(d) get heated and subsequently get damaged

Ans: d

17. 5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the following r.p.m.
Which motor will be the costliest ?
(a) 730 r.p.m.
(b) 960 r.p.m. (c) 1440 r.p.m. (d) 2880 r.p.m

. Ans: a

18. A 3-phase slip ring motor has
(a) double cage rotor
(6) wound rotor
(c) short-circuited rotor
(d) any of the above

Ans: b

19. The starting torque of a 3-phase squirrel cage induction motor is
(a) twice the full load torque
(b) 1.5 times the full load torque
(c) equal to full load torque

Ans: b

20. Short-circuit test on an induction motor cannot be used to determine
(a) windage losses
(b) copper losses
(c) transformation ratio
(d) power scale of circle diagram

Ans: a

Three Phase induction motor mcq part-2

1. An induction motor is identical to
(a) D.C. compound motor
(b) D.C. series motor
(c) synchronous motor
(d) asynchronous motor

Ans: d

2. The injected e.m.f. in the rotor of induction motor must have
(a) zero frequency
(b) the same frequency as the slip fre-quency
(c) the same phase as the rotor e.m.f.
(d) high value for the satisfactory speed control

Ans: b

3. Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ?
(a) By changing the number of stator poles
(b) Rotor rheostat control
(c) By operating two motors in cascade
(d) By injecting e.m.f. in the rotor circuit

Ans: a

4. The crawling in the induction motor is caused by
(a) low voltage supply
(b) high loads
(c) harmonics develped in the motor
(d) improper design of the machine
(e) none of the above

Ans: c

5. The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type
(a) star connected only
(b) delta connected only
(c) (a) and (b) both
(d) none of the above

Ans: c

6. The torque developed in the cage induction motor with autostarter is
(a) k/torque with direct switching
(6) K x torque with direct switching
(c) K2 x torque with direct switching
(d) k2/torque with direct switching

Ans: c

7. When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be
considered
(a) in series
(b) in parallel
(c) in series-parallel
(d) in parallel with stator

Ans: b

8. It is advisable to avoid line-starting of induction motor and use starter because
(a) motor takes five to seven times its full load current
(b) it will pick-up very high speed and may go out of step
(c) it will run in reverse direction
(d) starting torque is very high

Ans: a

9. Stepless speed control of induction motor is possible by which of the following methods ?
(a) e.m.f. injection in rotor eueuit
(b) Changing the number of poles
(c) Cascade operation
(d) None of the above

Ans: b

10. Rotor rheostat control method of speed control is used for
(a) squirrel-cage induction motors only
(b) slip ring induction motors only
(c) both (a) and (b)
(d) none of the above

Ans: b

11. In the circle diagram for induction motor, the diameter of the circle represents
(a) slip
(b) rotor current
(c) running torque
(d) line voltage

Ans: b

12. For which motor the speed can be controlled from rotor side ?
(a) Squirrel-cage induction motor
(b) Slip-ring induction motor
(c) Both (a) and (b)
(d) None of the above

Ans: b

13. If any two phases for an induction motor are interchanged
(a) the motor will run in reverse direction
(b) the motor will run at reduced speed
(c) the motor will not run
(d) the motor will burn

Ans: a

14. An induction motor is
(a) self-starting with zero torque
(b) self-starting with high torque
(c) self-starting with low torque
(d) non-self starting

Ans: c

15. The maximum torque in an induction motor depends on
(a) frequency
(b) rotor inductive reactance
(c) square of supply voltage
(d) all of the above

Ans: d

16. In three-phase squirrel-cage induction motors
(a) rotor conductor ends are short-circuited through slip rings
(b) rotor conductors are short-circuited through end rings
(c) rotor conductors are kept open
(d) rotor conductors are connected to insulation

Ans: b

17. In a three-phase induction motor, the number of poles in the rotor winding is always
(a) zero
(b) more than the number of poles in stator
(c) less than number of poles in stator
(d) equal to number of poles in stator

Ans: d

18. DOL starting of induction motors is usually restricted to
(a) low horsepower motors
(b) variable speed motors
(c) high horsepower motors
(d) high speed motors

Ans: a

19. The speed of a squirrel-cage induction motor can be controlled by all of the following except
(a) changing supply frequency
(b) changing number of poles
(c) changing winding resistance
(d) reducing supply voltage

Ans: c

20. The 'crawling" in an induction motor is caused by
(a) high loads
(6) low voltage supply
(c) improper design of machine
(d) harmonics developed in the motor

Ans: d

Transformer mcq part-3

1. The use of higher flux density in the transformer design
(a) reduces weight per kVA
(6) reduces iron losses
(c) reduces copper losses
(d) increases part load efficiency

Ans: a

2. The chemical used in breather for transformer should have the quality of
(a) ionizing air
(b) absorbing moisture
(c) cleansing the transformer oil
(d) cooling the transformer oil.

Ans: b

3. The chemical used in breather is
(a) asbestos fibre
(b) silica sand
(c) sodium chloride
(d) silica gel

Ans: d

4. An ideal transformer has infinite values of primary and secondary inductances. The statement is
(a) true
(b) false

Ans: b

5. The transformer ratings are usually expressed in terms of
(a) volts
(b) amperes
(c) kW
(d) kVA

Ans: d

6. The noise resulting from vibrations of laminations st by magnetic forces, is termed as
(a) magnetostrication
(b) boo
(c) hum
(d) zoom

Ans: c

7. Hysteresis loss in a transformer varies as (Bmax = maximum flux density)
(a) Bmax
(b) Bmax^1-6
(C) Bmax^1-83
(d) Bmax.r

Ans: b

8. Material used for construction of transformer core is usually
(a) wood
(b) copper
(c) aluminium
(d) silicon steel

Ans: d

9. The thickness of laminations used in a transformer is usually
(a) 0.4 mm to 0.5 mm
(b) 4 mm to 5 mm
(c) 14 mm to 15 mm
(d) 25 mm to 40 mm

Ans: a

10. The function of conservator in a transformer is
(a) to project against'internal fault
(b) to reduce copper as well as core losses
(c) to cool the transformer oil
(d) to take care of the expansion and contraction of transformer oil due to variation of temperature of sur-roundings

Ans: d

11. The highest voltage for transmitting electrical power in India is
(a) 33 kV.
(6) 66 kV
(c) 132 kV
(d) 400 kV

Ans: d

12. In a transformer the resistance between its primary and secondary is
(a) zero
(b) 1 ohm
(c) 1000 ohms
(d) infinite

Ans: d

13. A transformer oil must be free from
(a) sludge
(b) odour
(c) gases
(d) moisture

Ans: d

14. A Buchholz relay can be installed on
(a) auto-transformers
(b) air-cooled transformers
(c) welding transformers
(d) oil cooled transformers

Ans: d

15. Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds
(a) 50°C
(b) 80°C
(c) 100°C
(d) 150°C

Ans: d

16. The main reason for generation of harmonics in a transformer could be
(a) fluctuating load
(b) poor insulation
(c) mechanical vibrations
(d) saturation of core

Ans: d

17. Distribution transformers are generally designed for maximum efficiency around
(a) 90% load
(b) zero load
(c) 25% load
(d) 50% load

Ans: d

18. Which of the following property is not necessarily desirable in the material for transformer core ?
(a) Mechanical strength
(6) Low hysteresis loss
(c) High thermal conductivity
(d) High permeability

Ans: c

19. Star/star transformers work satisfactorily when
(a) load is unbalanced only
(b) load is balanced only
(c) on balanced as well as unbalanced loads
(d) none of the above

Ans: b

20. Delta/star transformer works satisfactorily when
(a) load is balanced only
(b) load is unbalanced only
(c) on balanced as well as unbalanced loads
(d) none of the above

Ans: c

Transformer Mcq part -2

1. Efficiency of a power transformer is of the order of
(a) 100 per cent
(b) 98 per cent
(c) 50 per cent
(d) 25 per cent

Ans: b

2. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are
(a) friction and windage losses
(b) copper losses
(c) hysteresis and eddy current losses
(d) none of the above

Ans: c

3. A common method of cooling a power transformer is
(a) natural air cooling
(b) air blast cooling
(c) oil cooling
(d) any of the above

Ans: c

4. The no load current in a transformer lags behind the applied voltage by an angle of about
(a) 180°
(b) 120"
(c) 90°
(d) 75°

Ans: d

5. In a transformer routine efficiency depends upon
(a) supply frequency
(b) load current
(c) power factor of load
(d) both (b) and (c)

Ans: d

6. In the transformer the function of a conservator is to
(a) provide fresh air for cooling the transformer
(b) supply cooling oil to transformer in time of need
(c) protect the transformer from damage when oil expends due to heating
(d) none of the above

Ans: c

7. Natural oil cooling is used for transformers upto a rating of
(a) 3000 kVA
(b) 1000 kVA
(c) 500 kVA
(d) 250 kVA

Ans: a

8. Power transformers are designed to have maximum efficiency at
(a) nearly full load
(b) 70% full load
(c) 50% full load
(d) no load

Ans: a

9. The maximum efficiency of a distribution transformer is
(a) at no load
(b) at 50% full load
(c) at 80% full load
(d) at full load

Ans: b

10. Transformer breaths in when
(a) load on it increases
(b) load on it decreases
(c) load remains constant
(d) none of the above

Ans: b

11. No-load current of a transformer has
(a) has high magnitude and low power factor
(b) has high magnitude and high power factor
(c) has small magnitude and high power factor
(d) has small magnitude and low power factor

Ans: d

12. Spacers are provided between adjacent coils
(a) to provide free passage to the cool¬ing oil
(b) to insulate the coils from each other
(c) both (a) and (b)
(d) none of the above

Ans: a

13. Greater the secondary leakage flux
(a) less will be the secondary induced e.m.f.
(b) less will be the primary induced e.m.f.
(c) less will be the primary terminal voltage
(d) none of the above

Ans: a

14. The purpose of providing iron core in a step-up transformer is
(a) to provide coupling between primary and secondary
(b) to increase the magnitude of mutual flux
(c) to decrease the magnitude of mag-netizing current
(d) to provide all above features

Ans: c

15. The power transformer is a constant
(a) voltage device
(b) current device
(c) power device
(d) main flux device

Ans: d

16. Two transformers operating in parallel will share the load depending upon their
(a) leakage reactance
(b) per unit impedance
(c) efficiencies
(d) ratings

Ans: b

17. If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be
(a) R₂/VK
(b) R₂/K²
(c) R₂/K
(d) R/K₂

Ans: b

18. What will happen if the transformers working in parallel are not connected with regard to polarity ?
(a) The power factor of the two trans-formers will be different from the power factor of common load
(b) Incorrect polarity will result in dead short circuit
(c) The transformers will not share load in proportion to their kVA ratings
(d) none of the above

Ans: b

19. Ifthe percentage impedances of the two transformers working in parallel are different, then
(a) transformers will be overheated
(b) power factors of both the trans-formers will be same
(c) parallel operation will be not possible
(d) parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load

Ans: d

20. In a transformer the tappings are generally provided on
(a) primary side
(b) secondary side
(c) low voltage side
(d) high voltage side

Ans: d

DC MOTOR MCQ PART-3

1. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor

Ans: c

2. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
(a) nothing will happen to th£ motor
(b) this will make armature to take heavy current, possibly burning it
(c) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses (d) motor will run at very slow speed

Ans: c

3. D.C. series motors are used
(a) where load is constant
(b) where load changes frequently
(c) where constant operating speed is needed
(d) in none of the above situations.

Ans: d

4. For the same H.P. rating and full load speed, following motor has poor starting torque
(a) shunt
(b) series
(c) differentially compounded
(d) cumulativeAlyc'ompounded

Ans: c

5. In case of conductively compensated D.C. series motors, the compensating winding is provided
(a) as separately wound unit
(6) in parallel with armature winding
(c) in series with armature winding
(d) in parallel with field winding

Ans: c

6. Sparking at the commutator of a D.C. motor may result in
(a) damage to commutator segments
(b) damage to commutator insulation
(c) increased power consumption
(d) all of the above

Ans: d

7. Which of the following motor is preferred for operation in highly explosive atmosphere ?
(a) Series motor
(b) Shunt motor
(c) Air motor
(d) Battery operated motor

Ans: c

8. If the supply voltage for a D.C. motor is increased, which of the following will decrease
?
(a) Starting torque
(b) Operating speed
(c) Full-load current
(d) All of the above

Ans: c

9. Which one of the following is not the function of pole shoes in a D.C. machine ?
(a) To reduce eddy current loss
(b) To support the field coils
(c) To spread out flux for better unifor-mity
(d) To reduce the reluctance of the mag-netic path

Ans: a

10. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
(a) 4.0
(b) 2.0
(c) 1.0
(d) 0.5

Ans: d

11. The condition for maximum power in case of D.C. motor is
(a) back e.m.f. = 2 x supply voltage
(b) back e.m.f. =1/2x supply voltage
(c) supply voltage = 1/2x back e.m.f.
(d) supply voltage = back e.m.f.

Ans: b

12. For which of the following applications a D.C. motor is preferred over an A.C. motor ?
(a) Low speed operation
(b) High speed operation
(c) Variable speed operation
(d) Fixed speed operation

Ans: c

13. In D.C. machines the residual magnetism is of the order of
(a) 2 to 3 per cent
(6) 10 to 15 per cent
(c) 20 to 25 per cent
(d) 50 to 75 per cent

Ans: a

14. Which D.C. motor is generally preferred for cranes and hoists ?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor

Ans: a

15. Three point starter can be used for
(a) series motor only
(b) shunt motor only
(c) compound motor only
(d) both shunt and compound motor

Ans: d

16. Sparking, is discouraged in a D.C. motor because
(a) it increases the input power con-sumption
(b) commutator gets damaged
(c) both (a) and (b)
(d) none of the above

Ans: b

17. Speed control by Ward Leonard method gives uniform speed variation
(a) in one direction
(b) in both directions
(c) below normal speed only
(d) above normal speed only.

Ans: b

18. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have
to be
(a) level compounded
(b) under compounded
(c) cumulatively compounded
(d) differentially compounded

Ans: c

19. Following motor is used where high starting torque and wide speed range control is required.
(a) Single phase capacitor start
(b) Induction motor
(c) Synchronous motor
(d) D.C. motor
(e) None of the above

Ans: d

20. In a differentially compounded D.C. motor, if shunt field suddenly opens
(a) the motor will first stop and then run in opposite direction as series motor
(b) the motor will work as series motor and run at slow speed in the same direction
(c) the motor will work as series motor and run at high speed in the same direction
(d) the motor will not work and come to stop

Ans: a

DC MOTOR MCQ PART-2

1. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
(a) The motor will stop
(b) The motor will continue to run
(c) The armature may burn
(d) The motor will run noisy

Ans: c

2. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
(a) back e.m.f. is equal to armature drop
(b) armature drop is negligible
(c) flux is proportional to armature current
(d) flux is practically constant in D:C. shunt motors

Ans: d

3. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
(a) almost negligible
(b) rated full-load current
(c) less than full-load current
(d) more than full-load current

Ans: d
4. These days D.C. motors are widely used in
(a) pumping sets
(b) air compressors
(c) electric traction
(d) machine shops

Ans: c

5. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
(a) Frame
(b) Shaft
(c) Commutator
(d) Stator

Ans: c

6. In which of the following applications D.C. series motor is invariably tried?
(a) Starter for a car
(b) Drive for a water pump
(c) Fan motor
(d) Motor operation in A.C. or D.C.

Ans: a

7. In D.C. machines fractional pitch winding is used
(a) to improve cooling
(b) to reduce copper losses
(c) to increase the generated e.m.f.
(d) to reduce the sparking

Ans: d

8. A three point starter is considered suitable for
(a) shunt motors
(b) shunt as well as compound motors
(c) shunt, compound and series motors
(d) all D.C. motors

Ans: b

9. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
(a) 100%
(b) around 90%
(c) anywhere between 75% and 90%
(d) less than 50%

Ans d
:
10. The ratio of starting torque to full-load torque is least in case of
(a) series motors
(b) shunt motors
(c) compound motors
(d) none of the above

Ans: b

12. In D.C. motor which of the following can sustain the maximum temperature rise?
(a) Slip rings
(b) Commutator
(c) Field winding
(d) Armature winding

Ans: c

13. Which of the following law/rule can he used to determine the direction of rotation of
D.C. motor ?
(a) Lenz's law
(b) Faraday's law
(c) Coloumb's law
(d) Fleming's left-hand rule

Ans: d

14. Which of the following load normally needs starting torque more than the rated torque?
(a) Blowers
(b) Conveyors
(c) Air compressors
(d) Centrifugal pumps

Ans: b

15. The starting resistance of a D.C. motor is generally
(a) low
(b) around 500 Q
(c) 1000 Q
(d) infinitely large

Ans: a

16. The speed of a D.C. series motor is
(a) proportional to the armature current
(b) proportional to the square of the armature current
(c) proportional to field current
(d) inversely proportional to the armature current

Ans: d

17. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal
to
(a) 100% of the previous value
(b) 50% of the previous value
(c) 25% of the previous value
(d) 10% of the previous value
(e) none of the above

Ans: c

18. The current drawn by the armature of D.C. motor is directly proportional to
(a) the torque required
(b) the speed of the motor
(c) the voltage across the terminals
(d) none of the above

Ans: a

19. The power mentioned on the name plate of an electric motor indicates
(a) the power drawn in kW
(b) the power drawn in kVA
(c) the gross power
(d) the output power available at the shaft

Ans: d

20. Which D.C. motor has got maximum self loading property?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded 'motor
(d) Differentially compounded motor

Ans: d

DC GENERATOR MCQ PART-3

1. Which of the following statement about D.C. generators is false ?
(a) Compensating winding in a D.C. machine helps in commutation
(b) In a D. C. generator interpoles winding is connected in series with the armature winding
(c) Back pitch and front pitch are both odd and approximately equal to the pole pitch
(d) Equilizing bus bars are used with parallel running of D.C. shunt generators

Ans: d

2. The demagnetising component of armature reaction in a D.C. generator
(a) reduces generator e.m.f.
(b) increases armature speed
(c) reduces interpoles flux density
(d) results in sparking trouble

Ans: a

3. Magnetic field in a D.C. generator is produced by
(a) electromagnets
(b) permanent magnets
(c) both (a) and (b)
(d) none of the above

Ans: a

4. The number of brushes in a commutator depends on
(a) speed of armature
(b) type of winding
(c) voltage
(d) amount of current to be collected

Ans: d

5. Compensating windings are used in D.C. generators
a) mainly to reduce the eddy currents by providing local short-circuits
(b) to provide path for the circulation of cooling air
(c) to neutralise the cross-magnetising effect of the armature reaction
(d) none of the above

Ans: c

6. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?
(a) Dummy coils
(b) Commutator
(c) Eye bolt
(d) Equilizer rings

Ans: b

7. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(a) using conductor of annealed copper
(b) using commutator with large number of segments
(c) using carbon brushes of superior quality
(d) using equiliser rings

Ans: c

8. In D.C. generators, lap winding is used for
(a) high voltage, high current
(b) low voltage, high current
(c) high voltage, low current
(d) low voltage, low current

Ans: b

9. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
(a) 2 : 3
(b) 3 : 1
(c) 3 : 2
(d) 1 : 3

Ans: b

10. The voltage drop for which of the following types of brush can be expected to be least ?
(a) Graphite brushes
(b) Carbon brushes
(c) Metal graphite brushes
(d) None of the above

Ans: c

11. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be
(a) E/2
(b) 2E
(c) slightly less than E
(d) E

Ans: b

12. In a D.C. generator the actual flux distribution depends upon
(a) size of air gap
(b) shape of the pole shoe
(c) clearance between tips of the ad¬jacent pole shoes
(d) all of the above

Ans:

13. The armature core of a D.C. generator is usually made of
(a) silicon steel
(b) copper
(c) non-ferrous material
(d) cast-iron

Ans: a

9.63. Satisfactory commutation of D.C. machines requires
(a) brushes should be of proper grade and size
(b) brushes should smoothly run in the holders
(c) smooth, concentric commutator properly undercut
(d) all of the above

Ans: d

14. Open circuited armature coil of a D.C. machine is
(a) identified by the scarring of the commutator segment to which open circuited coil is
connected
(b) indicated by a spark completely around the commutator
(c) both (a) and (b)
(d) none of the above

Ans: c

15. In a D.C. machine, fractional pitch winding is used
(a) to increase the generated voltage
(b) to reduce sparking
(c) to save the copper because of shorter end connections
(d) due to (b) and (c) above

Ans:

16. For the parallel operation of two or more D.C. compound generators, we should ensure that
(a) voltage of the incoming generator should be same as that of bus bar
(b) polarity of incoming generator should be same as that of bus bar
(c) all the series fields should be run in parallel by means of equilizer connection
(d) series fields of all generators should be either on positive side or negative side of the armature
(e) all conditions mentioned above should be satisfied

Ans: d

17. D.C. series generator is used
(a) to supply traction load
(b) to supply industrial load at constant voltage
(c) voltage at the toad end of the feeder
(d) for none of the above purpose

Ans: c

18. Following D.C. generator will be in a position to build up without any residual magnetism in the poles
(a) series generator
(b) shunt generator
(c) compound generator
(d) self-excited generator

Ans: d

19. Interpole flux should be sufficient to
(a) neutralise the commutating self induced e.m.f.
(b) neutralise the armature reaction flux
(c) neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
(d) perform none of the above functions

Ans: c

20. D.C. generator generally preferred for charging automobile batteries is
(a) series generator
(b) shunt generator
(c) long shunt compound generator
(d) any of'the above

Ans: c

Control system mcq part -1

1. In an open loop control system
(a) Output is independent of control input
(b) Output is dependent on control input
(c) Only system parameters have effect on the control output
(d) None of the above

Ans: a

2. For open control system which of the following statements is incorrect ?
(a) Less expensive
(b) Recalibration is not required for maintaining the required quality of the
output
(c) Construction is simple and maintenance easy
(d) Errors are caused by disturbances

Ans: b

3. A control system in which the control action is somehow dependent on the output is known as
(a) Closed loop system
(b) Semiclosed loop system
(c) Open system
(d) None of the above

Ans: a

4. In closed loop control system, with positive value of feedback gain the overall gain of the system will
(a) decrease
(b) increase
(c) be unaffected
(d) any of the above

Ans: a

5. Which of the following is an open loop control system ?
(a) Field controlled D.C. motor
(b) Ward leonard control
(c) Metadyne
(d) Stroboscope

Ans: a

6. Which of the following statements is not necessarily correct for open control system ?
(a) Input command is the sole factor responsible for providing the control
action
(b) Presence of non-linearities causes malfunctioning
(c) Less expensive
(d) Generally free from problems of non-linearities

Ans: b

7. In open loop system
(a) the control action depends on the size of the system
(b) the control action depends on system variables
(c) the control action depends on the input signal
(d) the control action is independent of the output

Ans: d

8.----has tendency to oscillate.
(a) Open loop system
(b) Closed loop system
(c) Both (a) and (b)
(d) Neither (a) nor (b)

Ans: b

9. A good control system has all the following features except
(a) good stability
(b) slow response
(c) good accuracy
(d) sufficient power handling capacity

Ans: b

10. A car is raining at a constant speed of 50 km/h, which of the following is the feedback element for the driver ?
(a) Clutch
(b) Eyes
(c) Needle of the speedometer
(d) Steering wheel
(e) None of the above

Ans: c

11. The initial response when tne output is not equal to input is called
(a) Transient response
(b) Error response
(c) Dynamic response
(d) Either of the above

Ans: a

12. A control system working under unknown random actions is called
(a) computer control system
(b) digital data system
(c) stochastic control system
(d) adaptive control system

Ans: c

13. An automatic toaster is a ______ loop control system.
(a) open
(b) closed
(c) partially closed
(d) any of the above

Ans: a

14. Any externally introduced signal affecting the controlled output is called a
(a) feedback
(b) stimulus
(c) signal
(d) gain control

Ans: b

15. A closed loop system is distinguished from open loop system by which
of the following ?
(a) Servomechanism
(b) Feedback
(c) Output pattern
(d) Input pattern

Ans: b

16. ----is a part of the human temperature control system.
(a) Digestive system
(b) Rerspiration system
(c) Ear
(d) Leg movement

Ans: b

17. By which of the following the control action is determined when a man walks along a path ?
(a) Brain
(b) Hands
(c) Legs
(d) Eyes

Ans: d

18.--- is a closed loop system.
(a) Auto-pilot for an aircraft
(6) Direct current generator
(c) Car starter
(d) Electric switch

Ans: a

19. Which of the following devices are commonly used as error detectors in instruments ?
(a) Vernistats
(b) Microsyns
(c) Resolvers
(d) Any of the above

Ans: d

20. Which of the following should be done to make an unstable system stable ?
(a) The gain of the system should be decreased
(b) The gain of the system should be increased
(c) The number of poles to the loop transfer function should be increased
(d) The number of zeros to the loop transfer function should be increased

Ans: b