Hi All,
I am posting the answers for this bits.I am not giving explanation for answers..For detailed explanation please go through the hard copy ......
I am posting the answers for this bits.I am not giving explanation for answers..For detailed explanation please go through the hard copy ......
BEE
JNTUH PREVIOUS BITS
UNIT-5(DC generators)
1. 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
2. The emf produced in the dc generator is ____ induced emf [b ]
(a) Statically (b) Dynamically (c) magnetically (d) Electrostatically
3. DC generator operates on the principle of [ a]
(a) Electromagnetic induction (b) Lenz's law (c) Biot Savart's law (d) none of these
4. Emf equation of generator is
5. Yoke is made of which material Cast iron or Cast steel
6. Types of windings in dc generator Lap winding ,wave winding
7. The Mechanical energy source used to drive a dc generator is called a [ B ]
(A) Rotor (B) Prime Mover (C) Alternator (D) Motor drive
8. The nature of current having in the armature of a dc machine is _____ [ a ]
a) AC b) DC c) pulsating d) None
9. The induced voltage in a single loop reverses_____ [ a ]
a) Once each revolution b) once each half revolution
c) one each quarter revolution d) 8 times each revolution
c) one each quarter revolution d) 8 times each revolution
10. The field of self excited generator is excited by [ c]
a) Dc b) Ac c) By its own current d) Either ac or Dc
11. The magnetic field which initially induces emf in the armature in a self excited dc generator is Because of Residual magnetism(residual flux)
12. 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
C) A pulsating emf D) Emf of random waveshape
13. 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.
14. Faraday's second Law states that the magnitude of individual emf is equal to the rate of Change of flux linkages.
15. A four pole DC generator is running at 1500 rpm. The frequency of current in the armature is 50
16. The armature of a dc machine is a laminated to reduce Eddy current losses
17. The function of interpoles in a dc machine is to improve commutation
18. The EMF induced in a coil rotating in a uniform magnetic field is maximum when the flux linkage by the coil is Minimum
UNIT-5(DC Motors)
1. 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
2. Fleming's left hand rule is applicable for: [ b ]
(a) dc generator (b) dc motor (c) alternator (d) Transformer
3. The armature torque of the dc shunt motor is proportional to [ c ]
(a) armature current only (b) field flux only (c) armature current and flux both (d) None
4. Motor which should not run at no-load is [ a]
(a) Series motor (b) shunt motor (c) compound motor (d) induction motor
5. Yoke is made of which material Cast iron or cast steel
6. Losses in DC machine are Iron losses,Copper losses,Mechanical losses
7. Types of DC motors Dc series motor,DC shunt motor,DC compound motor
8. In DC shunt motor the Torque is directly propotional to Ø * Ia
9. 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
10. A Commutator in a DC machine can convert ____ to ______ [c ]
(a) AC, DC (b) DC, AC (c) either ‘A’ or ‘B’ (d) None
11.The current flowing through armature conductors of a dc motor is
_____________ [ c ]
_____________ [ c ]
a) Pulsating b) Dc c) Ac d) none of these
12. 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
13. 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
14. The starting resistance for a dc shunt motor Low
15. A 3 point starter is considered suitable for dc Shunt motor
16. 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
17. 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
18. 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
19. The starting torque of a dc shunt motor is [ B]
A) Zero B) low C) high D) very high.
20. The armature of a dc machine is a laminated to reduce Eddy current losses
21. If the flux of a dc motor approaches zero its speed will___be infinite
22. The direction of mechanical force experienced on a current carrying conductor placed in a magnetic Field is determined by Fleming left hand rule
23. The function of interpoles in a dc machine is to Improve commutation
24 The speed of a DC motor is directly proportional to its Back emf(Eb) and inversely proportional to Flux(Ø)
25. The current drawn by a dc motor at the starting instant will be High
26. The eddy current losses is directly proportional to [b ]
a) f b)f^2 c)f^1.6 d)f^3
27. The iron losses [ d ]
a) core losses b) eddycurrent losses c) hystersis losses d) all the above
28. 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
29. The collection of current from armature conductors to the external load is the function of Brushes and commutator
30. The iron or core losses are also known as Constant losses
31. In d.c motor unidirectional torque is produced with the help of Brushes and commutator.
32. Between no load and full load -------motor develops the least torque
33. Under constant load conditions ,the speed of a d.c motor is affected by V,Ra,Ø
34. The Eb/V ratio of a d.c motor known as Efficiency
35.An invertor is employed to convert D.C voltage to A.C voltage
UNIT-7: 3-phase induction motors
1. Difference in speed between stator field and rotor [ c]
(a) Full load speed (b)No load speed (c)Slip (d) Regulation
2. When rotor is at standstill [ b ]
(a) slip is zero (b) slip is one (c) Any slip (d) Slip is infinity
3. Slip= (Ns –N)/(Ns)
4. Types of rotors in 3-phase induction motor Slipring ,Squirrel cage
5. The relationship between rotor frequency, f2, slip (s) and the stator frequency (f1) is = f2=sf1
6. The speed of rotor field of an Induction Motor is Ns*(1-S)
7. The synchronous speed of 50 Hz, 4 pole induction motor is 1500RPM
8. The value of slip of Induction motor at synchronous speed will be 0(Zero)
9. An induction motor works with _____. [ b]
a) DC only b) AC only c) both AC & DC d) None
10.In an Induction motor, the torque is related to supply voltage as V2
11. The synchronous speed of a 2 pole 3 phase induction motor for supply frequency of 60 Hz is 3600 RPM
12. The number of slip rings on a 3 phase wound rotor induction motor is ____ . [ a]
a) 3 b) 2 c) 6 d) None
Unit-8: Basic instruments.
1. PMMC is used for measuring [ a]
(a) DC (b)AC (c) AC&DC (d)None
2. MI instrument is used to measure [ c]
(a) AC (b) DC (c) AC&DC (d) NONE
3. Example of absolute instrument Tangent ray galvanometer
4. Example of integrating instrument Energy meter
5. An ohm-meter is an ____ type instrument. [ a ]
a) Dynamo meter b) moving coil c) Moving iron d) Induction
6. A meter that is capable of measuring DC only is ____ [ a ]
a) Moving Coil b) Moving Iron c) Thermo Couple d) None
7. When the instrument is over damped it will become Lethargic
8. An instrument that measures electrical energy is an Integrating type instrument
9. The damping usually provided in indicating instruments having weak magnetic field is [ a ]
a) air friction b) fluid friction c) hysteresis d) eddy current
10. Gravity controlled instruments are always used in Vertical position
11. In indicating instruments the damping is usually adjusted [ a ]
a)at critical value b) to the value slightly higher than critical value
c)to the value slightly below critical value d) to any value
12. A Moving iron ammeter, when used on AC circuit, indicates RMS value of current.
13. In gravity control, the controlling torque is a function of angular deflection, as __i proportional to theta(angle of deflection)___.