1. A 12 V automobile light is rated at 30 W. The total charge that flows through the filament in one minute is
2. If the length of a wire of resistance R is uniformly stretched to n times its original value, its new resistance is:
3. The hot resistance of filament of a bulb is higher than the cold resistance because the temperature co- efficient of the filament is:
4. Twelve 1 ohm resistances are used as edges to form a cube. The resistance between two diagonally opposite corners of the cube is :
5. Kirchhoff’s current law is applicable to
(1) Closed loops in a circuit
(2) Junction in a circuit
(3) Magnetic circuits
Which of the above statement/s is / are correct ?
6. A conductor of d diameter, length l consumes a power of W when a current I flows through it. What will be power consumed if d is doubled, l is halved and current is tripled ?
7. While determining RTH of a circuit:
8. Two charges are placed at a small distance apart. If a glass slab is placed between them, the force between the charges will:
9. The polential inside a charged hollow sphere is:
10. The rms value of the resultant current in a wire which carries a dc current of 10A and sinusoidal alternating current of peak value 20A is:
11. The resistance of a 1 kW electric heater when energized by a 230V. 1-phase ac is :
12. A 10 mH inductor carries a sinusoidal current of 1A rms at a frequency of 50Hz. The average power dissipated by the inductor is.
13. The power factor of an ac circuit lies between:
14. A single phase ac voltage source has 200 V rms and a system connected consumes an active power of 300 W. What is the reactive power consumed by the system if 2.5 A rms current is drawn ?
15. With the increase in applied frequency, the dielectric loss in a material will :
16. A capacitor used for power factor correction in a single-phase circuit decreases.
17. In an ac series RLC circuit, the voltage across R and L is 20V, voltage across L and C is 9V and voltage across RCL is 15V. What is the voltage across C ?
18. In the series resonant circuit, maximum, voltage across L occurs at :
19. A parallel circuit is said to be in resonance when the admittance is purely :
20. A coil of resistance 10 and inductance 0.8H is connected to 200 V dc supply. The initial rate of change of current is:
21. The temperature co-efficient of resistance of a wire is 0.0008 °C. If the resistance of the wire is 8 ohm at 0 °C. What is the resistance at 100 °C ?
22. Specific resistance of a conductor depends upon :
23. EMF of a thermocouple depends upon the :
24. Susceptibility of a diamagnetic material is :
25. Dielectric strength of a material depends upon
26. Which of the following magnetic materials has the highest reluctance ?
27. The relative permeability is less than 1 in :
28. Soft iron is used in the manufacture of electromagnets because of its :
29. High frequency transformer cores are generally made of :
30. The magnetic field required to reduce the residual magnetization to zero is called :
31. The shape of B-H curve for air gap is:
32. Maganin alloy used for making resistors for laboratory instruments:
33. The capacitance per unit volume is maximum for:
34. The temperature co-efficient of a resistance of a doped semiconductor is :
35. Reverse saturation current in a germanium diode is of the order of:
36. A transformer transforms:
37. The core flux in transformer depends mainly on:
38. A 250kVA, 11000V/400V and 50Hz single phase transformer has 80 turns on the secondary, what is the maximum value of flux ?
39. A single phase transformer when supplied from 220V, 50Hz has eddy current loss of 50W. If the transformer is connected to a voltage of 330V, 50Hz, the eddy current loss will be:
40. The phasor diagram of a transformer on load can be drawn only if we know:
41. The percentage resistance and reactance of a transformer are 2% and 4% respectively at full load, 0.8 p. f. lagging, the approximate voltage regulation is: .
42. The transformer efficiency will be maximum at a power factor of:
43. The all day efficiency of a distribution transformer will be high with low :
44. A distribution transformer is selected on the basis of :
45. The winding used in a 3-phase shell type transformer is _______ type.
46. The most essential condition for parallel operation of two single phase transformers is that they should have the same
47. Two transformers when operating in parallel will share the load depending upon which of the following ?
48. Stray losses are sum of:
49. Which of the following is not a part of dc machine ?
50. What are slot wedges in a dc machine made of ?
51. A 4 pole generator with 16 coils has a two layer lap winding. The pole pitch is :
52. The purpose of providing dummy coils in the armature of a dc machine is to:
53. The coil span
54. When an electric train is moving down a hill, the dc motor will operate as a dc: (A) (B) (C) (D)
55. In a dc machine, the sparking between brushes and commutator surface may be due to :
56. The torque-speed characteristic of a dc shunt motor is :
57. The variable loss in a dc shunt machine is:
58. In swin burne’s test of determination of efficiency of a dc shunt machine, the no load input power supplies:
59. Which type of alternator is used in hydroelectric power stations ?
60. Harmonics in the emf generated in an alternator can be reduced by :
61. A 3-phase synchronous motor has:
62. When does a synchronous motor operate with leading power factor current ?
63. For V- curves for a synchronous motor the graph is drawn between:
64. Induction motor shaft is made of :
65. What is the material of slip-rings in an induction machine ?
66. In an induction motor if the air gap is increased
67. A three-phase 6 pole, 50Hz, induction motor is running at 5% slip. What is the speed of the motor ?
68. A 3-phase induction motor is operating at slip S. If its two supply loads are interchanged, then its slip at that instant will be
69. The frequency of rotor currents at standstill is equal to :
70. If the rotor current resistance is increased in an induction motor, the maximum torque will occur at :
71. The power factor of an induction motor operating at no load will have a value around
72. Presence of 5th harmonics in induction motor causes
73. Location of a surge tank, in an hydroelectric power station is near.
74. Turbines installed at Bhakra Nangal are
75. The average load factor of thermal power plant in India is
76. Reflector of a nuclear reactor are made of
77. ACSR conductors have
78. Which type of insulators are used on 132 kV transmission lines ?
79. The most common type of fault is
80. The electric braking system commonly employed in rolling mills, elevators and printing presses is
81. Electrode is not consumed in case of
82. The tips of the electrodes for spot welding are made of
83. Induction heating takes place in
84. The temperature inside a furnace is usually measured by :
85. Battery driven vehicles
86. According to fuse law, the current carrying capacity varies as :
87. In a fluorescent tube if only the ends of the tube remains lighted, it indicates that
88. Aluminum conductor cables can be joined by :
89. Which of the following distribution system is not normally used ?
90. HV transmission line uses :
91. Actual input applied to the system in case of closed loop system is :
92. The largest error between reference input and output during the transient period is called
93. By using feedback in control system, the sensitivity to parameter variation is improved. This is achieved at the rate of cost of :
94. The degree to which an instrument indicates the changes in the measured variable without dynamic error is :
95. Loading effect is primary caused by instruments having :
96. With the increase of reverse bias in a p-n diode, the reverse current:
97. A tunnel diode is best suited for:
98. The use of a capacitor filter in a rectifier circuit gives satisfactory performance only when the load
99. For a npn bipolar transistor, what is main stream of current in the base region ?
Explain:- Overview of Bipolar Junction Transistor (BJT)
A bipolar junction transistor (BJT) is a three-layer semiconductor device consisting of two p-n junctions. The BJT has three terminals, namely emitter, base, and collector. The emitter is heavily doped, and the collector is lightly doped compared to the emitter. The base region is very thin and lightly doped.
Working of NPN BJT
In an NPN transistor, the emitter is made up of n-type material, and the base is made up of p-type material. The collector is made up of n-type material. When a small current is applied to the base terminal, it allows the flow of majority carriers across the base region. The majority carriers in the emitter are electrons, and they flow towards the collector through the base region.
Mainstream of Current in Base Region
The base region of an NPN transistor is very thin and lightly doped. When a small current is applied to the base terminal, it allows the flow of majority carriers across the base region. The majority carriers in the emitter are electrons, and they flow towards the collector through the base region. However, some of these electrons recombine with the majority carriers in the base region (holes). This recombination is due to the fact that the base region is lightly doped, and hence, it has a low number of holes.
The main stream of current in the base region is due to the diffusion of holes. The electrons that flow towards the collector through the base region constitute only a small fraction of the total current that flows through the base region. The majority of the current in the base region is due to the diffusion of holes.
Conclusion
In conclusion, the main stream of current in the base region of an NPN bipolar transistor is due to the diffusion of holes. When a small current is applied to the base terminal, it allows the flow of majority carriers across the base region. The majority carriers in the emitter are electrons, and they flow towards the collector through the base region. However, some of these electrons recombine with the majority carriers in the base region (holes). The main stream of current in the base region is due to the diffusion of holes.