1. What is the magnetic force on the election, if it is placed in a union
magnetic field with zero initial velocity?
A: Zero.
2. What are the basic constituents in CRO?
A: CRT, power supplies, time base circuit, deflection amplifier.
3. what are the basic constituents in CRT?
A. electron gun, deflection system, fluorescent screen, glass envelop.
4. which type of fluorescent material is used to provide a green spot on the screen>
A. Zinc ortho silicate.
5. what is the purpose of focusing?
A.focusing is required to produce a dominant spot on the screen.
6. define valence electrons?
A. the electrons in the outermost orbit of an atom are known as valence electrons.
7. give the example for conductors, semi conductors and insulators?
A. conductors: copper, aluminium
Semi conductors: silicon, germanium
Insulators: wood, glass
8. what is meant by forbidden energy gap?
A. the separation between conduction band and valence band in the energy level diagram is known as forbidden energy gap.
9. what is meant by intrinsic semiconductor?
A. if the semi conductor is in pure form then it is known as an intrinsic semiconductor.
10. define doping?
A. the process of adding the impurities to a pure semi conductor is called doping.
11. which type of impurities are added in the p-type semiconductor.
A. trivalent impurities.
12. define drift current?
A. because of the applied voltage, the electrons will collide with the atoms of semiconductor and moves in a random direction. This drift causes current to flow in the semiconductors. The current produced due to the drifting of free electrons is called drift current.
13. state law of mass action?
A. law of mass action states that the product of concentration of electrons (n) and holes (p) is always constant at a fixed temperature.
np=ni2 where ni is intrinsic concentration
14. define diffusion current?
A. the current due to the transport of charges in a semiconductor due to the non uniform concentration of charged particles is called diffusion current.
15. what is meant by mean life time of the charge carrier?
A. the amount of time between the creation and disappearance of a free electron or hole is called mean life time of the charge carrier.
16. what is meant by hall effect?
A. if a semiconductor carrying current ‘I’ is placed in a transverse magnetic field with flux density ‘B’ then an electric field ‘E’ is induced in the direction perpendicular to both I and B. this phenomenon is called hall effect.
17. for an ideal diode, what is the reverse resistance?
A. infinity.
18. mention the diode current equation?
A. I = I0(eV/ηVT-1)
19. what is the cut in voltage of a silicon diode?
A. 0.6 V
20. what are the breakdown mechanisms involved in PN diode and Zener diode?
A. PN diode -->avalanche breakdown
Zener diode --> zener breakdown
21. out of zener and PN diode which one is having doped?
A. zener.
22. what is breakdown voltage of a zener diode?
A. 6V
23. mention the applications of PN diode?
A. rectifier, switch, clamping circuit, clipping circuit.
24.mention the application of zener diode under reverse bias?
A. voltage regulator.
25. what is a rectifier?
A. rectifier is a device which converts Ac voltage to pulsating Dc voltage using one or more P-N function diodes.
26. what is the efficiency of half wave rectifier?
A. 40.6%.
27.define ripple factor?
A .the ratio of rms value of Ac component to the Dc component in the output is known as ripple factor.
28. what is the ripple factor of half wave rectifier?
A. 1.21
29. which rectifier has peak inverse value is 2Vm?
A. full wave centre tapped rectifier.
30. what is the out frequency in full wave bridge rectifier ( if fin is the input frequency)?
A. 2 fin
31. which type of transformers are used in rectifiers?
A. step down transformer.
32.what is the significance of arrow mark in a transistor?
A. arrow mark represents conventional current direction.
33. out of emitter, base and collector, which region is heavily doped?
A. emitter.
34. why collector is made more wider than that of emitter and base?
A. in order to dissipate the heat produced in it.
35. why transistor is called bi polar junction transistor?
A. because its current conduction depends on both majority charge carries and minority charge carriers.
36. what is the relationship between IE,IB and IC?
A. IE=IB+IC.
37.give an example for current controlled device?
A.BJT
38. define amplification factor?
A. it is defined as the ratio of output current to input current of a transistor.
39. why common emitter confismation is preferred compared to CB and CC?
A. because of its high voltage gain.
40. what is meant by early effect?
A. an increase in the collector base voltage increases the space charge width at the output junction (base-collector). This causes effective base width decrease, this phenomenon is known as the early effect.
41. what is the relationship between α, β and γ?
A. γ=1+β, β=α/1-α, γ=1/1-α.
42. which transistor confismation has low output resistance.
A. common collector.
43. what is the application of common collector configuration?
A. for impedance matching.
44. which transistor confismation has current gain less than unity.
A. common base α=IC/IE (IE is slightly greater than IC.
Important points regarding transistor naming:
Ex: BC 547
First letter (B) indicates nature of semiconductor material.
A=germanium, B=silicon, C=gallium arsenide, R=compound material
Second letter (C) indicates the device and circuit function.
A=diode, B=variable capacitance diode, C= A.F low powered transistor
D=A.F power transistor, G=tunnel diode, H=magnetic sensitive diode
L=H.F power transistor, K= Hall effect device , M=Hall effect modulator
P=radiation sensitive diode, Q=radiation generating diode, R=thyristor (SCR or triac), S=low power switching transistor, T=thyrister, power
Note : if the transistor contains 2 letters and 3 numbers it is for consumer equipment (ex: BC547), if it contains 3 letters and 2 numbers it is for industrial purpose( ex: BFX63).
45. what is the VBE sat value of a silicon transistor?
A. VBE sat(si)=0.7V
46. out of BJT and FET which one is the unipolar device?
A. FET, because its operation depends upon the flow of majority carriers only.
47. which MOSFET can be operated in both depletion and enhancement mode?
A. depletion MOSFET.
48. why MOSFET is called insulated safe FET?
A. the metal region of gate with insulating oxide layer of SiO2 forms a parallel plate capacitor. So the MOSFET is called the insulated gate FET.
49. give an example for voltage controlled device?
A. FET.
50. number of P-N junctions in a UJT?
A. one.
51. what is the other name of UJT?
A. double-based diode.
52. what is the range of η (intrinsic stand off ratio) in UJT?
A. η is between 0.51 and 0.82.
53. give the examples for negative resistance devices?
A. UJI, tunnel diode.
54. Mention the applications of UJT?
A. (i) UJT relaxation oscillator
(ii) over voltage detector.
55. What are the majority charge carrier in PNP transistor.
A. holes.
56. Define break over voltage in SCR?
A. it is the minimum forward voltage at which SCR starts conducting heavily with gate being open.
57. If the transistor is to be operated in saturation region. What are the biasing states
of input and output?
A. Input and output must be in forward bias state.
58. Define transistor biasing?
A. The proper flow of zero signal collector current and fue maintenance of proper collector emitter voltage during fue passage of signal is known as transistor biasing.
59. what is the resulting effect, if the operating point was chosen close to saturation
region?
A. positive peak clipping.
60.In which region the transistor operating point was fixed to avoid the distortion?
A. active region.
61. what is meant by stabilization?
A. for faithful amplification operating point must remain fixed making operating point independent of temperature changes and transistor replacement is known as stabilization.
62. define stability factor?
A. it is defined as the rate of chance of collector current IC with respect to the collector base leakage current ICO, keeping both IB and β constant S=∂IC/∂IO
63. what is the stability factor in fixed bias?
A. S=1+β
64. what is the drawback in fixed bias?
A. it has hish stability factor, means less stable. (thermal stability)
65. what is the stability factor in voltage divider bias?
A. S~ 1
66. what is meant by thermal runaway?
A. as temperature Is increased, which increases two collector current causes increase in power dissipation. This phenomenon is referred to as thermal runaway.
67. what is the condition for thermal stability?
A. VCE≤VCC/2
68.what is the purpose of an amplifier?
A. it is used to set large signal output from a small signal input.
69. why hi, hr, hf and ho are hybrid parameters?
A. all these are mixture of different units and haence referred to as hybrid parameters.
70.what is the formula for hfe in CE confismation?
A. hfe=∆IC/∆IB at VCE constant
71. In the analysis of single stage transistor amplifier using hybrid model , what are
the formulae for AI, AV, Ri and Y0 .
Ans. AI= (-hf /1+h0RL ) , AV=(AIRL/Ri ) , Ri =hi-(hrhf /((i/RL )+h0 ))
Y0=h0-(hfhr /RS+hi)
72. In simplified hybrid model of CC current , what is the formulae for AI and AV
A. AI = 1+hfe ,Av=1.
73. In simplified hybrid model of CB circuit , what are the formulae for Ri and Av .
A. Ri =hie /1+hfe , Av=hfeRL /hie
74. What is meant by negative feedback?
A. When input signal and part of output signal are out of phase then the feedback is called negative feedback.
75. Which type of amplifier is used in current series feedback amplifier?
A. Transconductance, Similarly current amplifier in current shunt, Voltage amplifier in voltage series.
Transresistance amplifier in voltage shunt.
Table: The input and output resistances of all the feedback amplifier compared to without feedback.
Ri R0
Current series increases increases
Current shunt decreases increases
Voltage series increases decreases
Voltage shunt decreases increases
76. In voltage amplifier, what is the gain formula with negative feedback.
A. Avf = Av/1+Avβ
Av- gain without feedback
β- feedback factor
77. What is the formula for input resistance with feedback in voltage series feedback
amplifier?
A. Rif = Ri (1+βAvf)
78. What is the formula for output resistance with feedback in current shunt feedback
amplifier?
A. Rof =R0(1+βAI).
79. What is Bark hausen Criterion.
A. |Aβ| =1 i.e., the magnitude of loop gain must be unity.
Phase angle =0⁰ or 360⁰
80. What are damped oscillations?
A. If the amplitude of the signal decreases with respect to the time of the signal , then the oscillations are called damped oscillations.
81. What is the Phase Shift produced by one RC combination in RC Phase shift
oscillator.
A. 60⁰.
82. What is the Phase Shift produced by a transistor?
A.180 ⁰.
83. Which type of feedback is used in oscillators?
A. Positive feedback.
84. What is the formula for frequency of oscillations produced in RC Phase shift
oscillator?
A. f=1/ (2πRC
6+4K))
6+4K)) Where K= R c /R
85. What is the formula of oscillations produced in Wien bridge oscillator.
A. f=1/(2π(
R1R2C1C2)) or f=1/2πRC
R1R2C1C2)) or f=1/2πRC Since R1=R2=R , C1=C2=C
86. what is the formula for frequency of oscillations produced in Hartley Oscillator?
A: f= 1/2π√C(L1+L2)
87. what is the formula for frequency of oscillations produced in Colpitts oscillator.
A: f=1/2π√L.C1C2/C1+C2
88. Which type of materials are used to manufacture thermistors.
A: Ceramic or polymer.
89. What are the other names of Varator diod?
A: Varicap or Taning diod or variable reactance diode.
90. what is the other name of tunnel diode?
A: Esaki diode.
91. Give the examples of photo conductive devices?
A: PN photo diode, PIN photo diode, photo transistor.
92. which semiconductor devices act like a diode and two transistors?
A: UJT.
93. what is the phenomenon involved in LED to emit the light?
A: Electroluminescence.
94. which materials are used to manufacture LEDs?
A: gallium phosphide(GaP),gallium arsenide phosphide(GaAsP).
95. what are the two liquid crystal materials used in display technology?
A: Nematic and Cholestric.
96. What are the types of LCDs?
A: i). Dynamic scattering type.
ii). Field effect type.
97. What is the forbidden energy gap for silicon?
A: |i|2ev.
98. Which amplifiers are involved in cascade amplifier?
A: CE&CB amplifiers.
99. What is the feedback factor for voltage shunt feedback amplifier?
A: β=If/Vo.
100. What is the typical value of resonant frequency of a crystal oscillator?
A: 3.275 MHZ.
1 comments:
The questions are very useful.. Thanks for publishing..
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