Refresher 3
Basic Electronics, Diodes and Transistors
1. In any communication system, amplifiers compensate the attenuation of the signals, what can
we done in order to improve the efficiency of an amplifier?
a. reducing the supply voltage
b. decreasing unwanted power loss
c. increasing supply current
d. reducing gload power
2. How does an ohmmeter behaves if its positive lead is connected to a cathode while negative
as to anode?
a. decreasing resistance
b. infinite high resistance
c. unstable resistance
d. very very low resistance
3. Negative feedback was developed by Harold Black and typically employed in amplifiers to
reduce what?
a. feedback fraction
b. error voltage
c. distortion
d. gains full control
4. Dynamic impedance of a parallel circuit is calculated by this formula.
a. L/CR
b. L/C
c. RL/C
d. LC/R
5. Which of the following refers to the characteristics of a magnetic line of force?
a. travels from south to north through the surrounding medium of a bar magnet
b. travels back and forth between north and south pole of a magnet
c. travels from north to south through the surrounding medium of the bar magnet
d. stay stationary between the north and the south pole of a bar magnet
6. If a transformer steps the impedance up, it steps the voltage________.
a. down
b. up
c. remains the same
d. fluctuating
7. Why is it that ordinary diode don t work properly at high frequencies?
a. because of forward bias
b. because of reverse bias
c. because of breakdown
d. because of charge storage
8. A varactor has its internal capacitance varies with the applied voltage. What will happen then if
we increase the reverse voltage being applied across the varactor?
a. the capacitance increases
b. the voltage crippled
c. its reactance increases
d. the varactor will emit light because it will be burnt
9. A current surge takes place when a power supply is first tuned in because
a. transformer core is suddenly magnetized
b. the diodes suddenly start to conduct
c. the filter capacitor must be initially charged
d. arcing takes place in the switch
10. Zener diodes are used in voltage regulation, as an engineer how are you going to describe
the breakdown voltage of a zener diode?
a. its increasing exponentially
b. its almost constant
c. it destroy the zener diode
d. well measured and apply to forward biased the zener diode
11. What is the purpose of coupling capacitor in a typical transistor amplifier?
a. increase the output impedance of the transistor
b. to increase the amplifier’s gain
c. pass ac and block any dc signal
d. protect the transistor from surges
12. When a pure semiconductor is heated, its resistance__________.
a. goes up
b. goes down
c. no change
d. becomes conductance
13. Most of the majority carriers from the emitter _________.
a. recombine in the base
b. recombine in the emitter
c. pass through the base and to the collector
d.pass the base and back to emitter
14. In some design of transistor amplifier, we usually shunt a capacitor across the emitter resistor,
what is the purpose of this action ?
a. forward bias the emitter
b. avoid voltage drop in the gain
c. reduce noise in the amplifier
d. additional stuff just to increase design’s complexity
15. For proper operation of the transistor, its collector should have___________.
a. proper forward bias
b. proper reverse bias
c. very small thickness
d. a LED, a red one for monitor and display
16. A circuit has a supply voltage of 0.65Volts forward biasing a silicon diode and a LED at the
output. What most likely will occur?
a. the LED wont light
b. the LED will blink and goes off
c. the LED light steadily
d. the LED changes its color from red, orange and then busted
17. Your functioning VOM is set to ohmmeter function, the positive lead is connected to the anode
of the LED and the negative lead is on the cathode terminal. The LED does not emit any light.
What does it imply?
a. its alright the LED will never light in that condition
b. the LED is busted
c. the battery of the VOM is depleted
d. the position of the leads is wrong so it wont light
18. It is the measure of the amount of load a machine can turn.
a. radian force
b. load factor
c. torque
d. tension
19. The concentration of minority carriers in case of N-type semiconductors mainly depends
upon
a. the purity of the semiconductor material
b. the doping technique
c. distribution of impurities in semiconductor material
d. the temperature of the material
20. As the temperature of the semiconductor increases
a. its resistivity increases
b. its conductivity increases
c. its atomic number decreases
d. its temperature coefficient becomes zero
21. A piece of silicon doped with 6 x 1015 aluminum atoms/cm3 and 3 x 1015 antimony
atoms/cm3. The resulting material will be
a. p-type with hole concentration more than electron concentration
b. p-type with electron concentration more than hole concentration
c. n-type with electron concentration more than hole concentration
d. n-type with hole concentration greater than electron concentration
22. Semiconductors are sensitive to
a. light energy
b. heat
c. magnetic energy
d. all of the above
23. Germanium is ________________.
a. amorphous solid
b. liquid crystal
c. crystalline
d. transitional soild
24. The diffusion current is proportional to
a. applied electric field
b. concentration gradient of charge carriers
c. inverse of the applied electric field
d. inverse of the concentration gradient of the charge carriers
25. Light falls on one end of a long open-circuited n-type semiconductor bar. For low level
injection, the hole current is due predominantly to
a. drift
b. diffusion
c. both drift and diffusion
d. light gyration
26 At absolute zero, a pure semiconductor behaves like an insulator because
a. forbidden energy gap is reduced
b. drift velocity of free electrons is very small
c. no free electrons are available for current conduction
d. recombination of holes and electrons is slow
27. In a color TV, there is sound but no picture but the screen is illuminated, which of the
following functional elements will most likely have failed?
a. Rf amplifier
b. tuner
c. video detector
d. deflection am[plifiers
28. ________is a device that stay on once triggered and store one of two conditions as a
digital circuit.
a. latch
b. gate
c. oscillator
d. integrator
29. For a good 0.05 uF paper capacitor, the ohmmeter reading should
a. Go quickly to 100 ohms approximately and remain there
b. show low resistance momentarily and back off to a very high resistance
c. show high resistance momentarily and then a very low resistance
d. the pointer does not move at all
30. Which of the following is true?
a. air capacitors have a black band to indicate the outside foil
b. mica capacitors are available in capacitance values of 1 to 10 uF
c. electrolytic capacitors must be connected in the correct polarity
d. ceramic capacitors must be connected in the correct polarity
31. Capacitance increases with
a. larger plate area and greater distance between plates
b. smaller plate area and greater distance between plates
c. larger plate area and lesser distance between plates
d. smaller plate area and greater distance between plates
32. Inductive reactance is measured in ohms because it
a. reduces the amplitude of the alternating current
b. increases the amplitude of the alternating current
c. increases the amplitude of direct current
d. has a back emf that opposes direct current
33. When current in a conductor increases, Lenz Law says that the self induced voltage will
a. tend to increase the amount of current
b. aid the applied voltage
c. produce current opposing the increasing current
d. aid the increasing current producing higher concentration
34. Direct current voltage is characterized by____________.
a. its value cannot be stepped up or down by transformer
b. easier to amplify
c. reverses polarity
d. signal input and output for amplifiers
35. A capacitive reactance close to zero indicates
a. a high resistance
b. large capacitance at high frequency
c. small capacitance at low frequency
d. small resistance
36. The dominant critical frequency of a 741-op amp is being controlled by_____________.
a. a coupling capacitor
b. a compensation capacitor
c. a bypass capacitor
d. a filter capacitor
37. When carrying out a soldering procedure in electronics work, it is necessary to
a. to use acid flux
b. use least amount of solder
c. clean all parts after soldering
d. use adequate but not excessive amount of heat
38. Defined as the ratio of the amount of magnetic flux linking a secondary coil compared to
the flux generated by the primary coil
a. coefficient of magnetism
b. magnetic coefficient
c. coefficient of coupling
d. coefficient of self inductance
39. How are networks able to transform one impedance to another?
a. resistance in the networks substitute for resistance in the load
b. matching network can cancel the reactive part of an impedance and change the value of
the resistive part of an impedance
c.the matching network introduces negative resistance to cancel the resistive part of an
impedance
d. matching network introduces transconductance to cancel the reactive part of the impedance
40. A law which states that the ratio of the thermal conductivity to the electric conductivity is
proportional to the absolute temperature for all metals
a. Wiedeman-Licuanan law
b. Wiedeman-Franz law
c. Wiedeman-Childs law
d. Wiedeman-Sisters law
41. What is the purpose of flux?
a. removes oxides from the surface to be joined
b. prevents oxidation during soldering
c. acid cleans printed circuit connections
d. both a and b
42. Why would the rate at which electrical energy is used in an circuit be less than the
product of the magnitude of the ac voltage and current?
a. because there are only resistances in the circuit
b. because there are no reactances on the circuit
c. because there is a phase angle that is greater than zero between the current and voltage
d. because there is a phase angle that is equal to zero between the current and voltage
43. An insulating element or material has the capability of _______.
a. storing high voltage
b. preventing short circuit between the conducting wires
c. storing high current
d. conducting small amount of current
44. Residual magnetism is_____________.
a. the external magnetic field when the current is flowing through the exciting coil
b. the flux density which exist in the iron core when the magnetic field intensity is reduced
to zero
c. the flux density which exist in the iron core when the magnetic field intensity is at its maximum
value
d. the flux density when the core is saturated
45. Load regulation is a measure of power supplies ability to keep a constant output under
conditions of changing
a. line voltage
b. current demand
c. temperature
d. oscillator frequency
46. Emitter region in a n NPN transistor is heavily doped than base region so that
a. flow across the base region will be mainly holes
b. flow across the base region will be mainly electrons
c. base current is low
d. base current is high
47. IGFET is a _______________.
a. linear device
b. square law device
c. half power device
d. bipolar device
48. For a half wave rectifier having an input of 50 Hz signal, what is the ripple frequency of
the output?
a. 25 Hz
b. 50 Hz
c. 100 Hz
d. 75 Hz
49. In an emitter follower circuit, where is the output taken from?
a. base
b. emitter
c.collector
d. drain
50. The atomic number of germanium is 32, the number of electrons in the outermost shell is
a. 2
b. 4
c. 6
d. 8
51. Metals approach superconductivity conditions
a. near absolute zero
b. near critical temperature
c. at triple point
d. under the condition of high temperature and pressure
52. Thermionic emissions of electrons is due to
a. electromagnetic field
b. electrostatic field
c. high temperature
d. photo-electric effect
53. The bulk resistance of a diode is
a. the resistance of the N-material only
b. the resistance of the P-material only
c. the resistance of the junction
d. the resistance of the p and the n material
54.As the temperature of a semiconductor is reduced to absolute zero
a. all electrons become free
b. all electrons cease to move
c. all valence electrons tend to remain in the valence band
d. all valence electrons shift in the forbidden gap
55. What is the maximum number of electrons in the third orbit?
a. 3
b. 12
c. 18
d. 8
56. Which of the following is a donor impurity element?
a. Phosphorus
b. Aluminum
c. Boron
d. Indium
57. Thermal runaway of a transistor occurs when
a. heat dissipation from transistor is excessive
b. transistor joints melt due to high temperature
c. there is excessive leakage current due to temperature rise
d. the transistor is on fire
58. Which transistor configuration is preferred for high input impedance and low output
impedance?
a. common emitter
b. common collector
c. common base
d. common gate
59. A quiescent state of a transistor implies
a. zero bias
b. no distortion
c. no output
d. no input signal
60. Which of the following is the fastest switching device?
a. JFET
b. MOSFET
c. BJT
c. PBNO
61. What is the most efficient type of amplifiers?
a. Class A c. Class C
b. Class B d. Class AB
62. It is the ratio of dc collector current to the dc emitter current.
a. dc beta or hFE c. dc gamma
b. dc alpha d. dc current gain
63. It is a transistor application used as an interface between a circuit with a high output
resistance and a low-resistance load
a. isolator b. circulator
c. buffer d. amplifier
64. What is the disadvantage of a half-wave rectifier?
a. Components are expensive b. Diodes must have a power rating
c. Output is difficult to filter d. Uses transformer
65. What is the voltage across a reversed biases diode ion series with a 10 V DC source and a 1
KΩ resistor?
a. 0 V b. 0.7 V
c. 0.3 V d. 10 V
66. A multiplier circuit has a 4 pairs of capacitor-diode, what is the output of the multiplier if the
input is 10 V p-p.
a. 10 Vp-p b. 30 Vp-p
c. 40Vp-p d. 80 Vp-p
67 Which class of amplifier has the most distortion?
a. Class A b. Class B
c. Class C d. Class D
68. Which of the statement is correct?
a. the product of VCE and IC must exceed the maximum power dissipation.
b. the product of VCE and IC must not exceed the maximum power dissipation.
c. the quotient of VCE and IC must exceed the maximum power dissipation.
d. the quotient of VCE and IC must not exceed the maximum power dissipation.
69. Determine the ac emitter resistance (r’ e) of a transistor that operates with a dc emitter
current of 3.13mA.
a. 8 ohms b. 12 ohms
c. 10 ohms d. 14 ohms
70. Semiconductors whose electron and hole concentrations are equal
a. Doped semiconductor b. Extrinsic semiconductor
c. Intrinsic semiconductor d. Equal semiconductor
71 Monolithic IC wafers are typically of_____
a. 1/8 inch diameter b. 1 inch diameter
c. ¼ inch diameter d. 2-inch diameter
72. With the rise in temperature of a PN junction, which of the following will increase?
a. Width of the depletion layer b. Junction barrier voltage
c. Reverse leakage current d. All of the above
73. Which element is a dopant for an N-type semiconductor?
a. Boron b. Indium
c. Aluminum d. Arsenic
74. What happens to the width of the depletion region of a pn junction when the doping level is
increased?
a. increases b. Remains the same
c. decreases d. vanishes
75. A half-wave rectifier is utilized across the line frequency, what is the output
frequency?
a. 60 Hz b. 0 Hz
c. 120 Hz d. 30 Hz
76 ________is a unipolar semiconductor device whose current is carried by the majority
carriers only.
a. FET b. BJT
c. Point contact transistor d. Zener diode
77. The terminals of a filed effect transistor (whether MOS or junction type enhancement or
depletion type), corresponding r4espectively to the emitter, base and collector of bipolar transistor
are
a. Anode, gate and cathode b. Input, power supply and output
c. Source, gate and drain d. Darin, channel and source
78.. What is the current carrying part of a field effect transistor?
a. source b. gate
c. channel d. drain
79. The JFET is
a. A unipolar design b. Current control device
c. A voltage control device d. A and c
80. The minimum value of VGS that will cause the drain current to drop to zero.
a. Pinch-off voltage b. Thermal voltage
c. 26 mV d. Gate-source cut-off voltage
81. The constant-current region of a FET lies between
a. Cut-off and saturation b. Cut-off and pinch-off
c. 0 and IDss d. Pinch-off and breakdown
82. The emission of electrons in vacuum tubes is achieved by
a. electrostatic field
b. magnetic field
c. heating
d. electron bombardment
83. What material is the anode of a vacuum tube usually made from?
a. tungsten
b. nickel
c. carbon
d. aluminum
84.In case of indirectly heated tubes, the filament of the vacuum tube is usually made from
a. nickel
b. fin
c. tungsten
d. foil
85. Vacuum tubes has fins and are usually found in the anode for what purpose?
a. collect maximum number of electrons
b. reduce escape electrons
c. eliminate rebounding of electrons
d. dissipate heat produced
86. The difference between the valence band and the conduction band of a semiconductor
is called
a. Energy density b. vacon
c. Band gap d. Extrinsic effect
87. Amount of energy needed to liberate electrons from the surface of metals.
a. Ionic discharge b. corona
c. workfunction d. potential
88. _________is an excess property of P-type semiconductor.
a. neutron b. proton
c. hole d. electron
89. What do you call the bond that hold the crystal?
a. ionic b. valent
c. covalent d. James
90. What type of bonds are formed by sharing the valence electrons with neighboring
atoms?
a. ionic b. valent
c. covalent d. James
91. Avalanche breakdown in a semiconductor diode occurs when
a. the potential barrier is reduced to zero
b. forward biased exceeds a certain value
c. reversed bias exceeds a certain value
d. forward current exceeds a certain value
92. Which of the following material finds application in light emitting diodes?
a. silicon
b. sulphur
c. phosphorus
d. gallium phosphide
93. Which of the following material is used for infrared LEDs?
a. gallium arsenide
b. calcium phosphide
c. silicon
d. H2O
94. Heaters for vacuum tubes normally take a voltage value of what?
a. 1V
b. 6.3 V
c.2.3 V
d. 220 V
95. If the effective value of a half wave rectified sine wave is 20. The average value of the wave
will be
a. 27.7
b. 18.8
c. 23.3
d. 12.7
96. The quality of a power supply is judge by
a. size
b. regulation
c. voltage
d. power
97. In radio receivers, excessive ripple causes
a. hum
b. change in frequency selection
c. reduced power consumption
d. no effect
98. What is the typical speed of a cassette tape for a tape recorder?
a. 1 inch/sec
b. 5 cm/sec
c. 1 7/8 inch /sec
d. 2 2/3 inch / sec
99. What is the typical impedance of a loudspeaker?
a. 1 ohm
b. 12 ohms
c. 100 ohms
d. 10000 ohms
100. What will be the dB gain for an increase of power level from 13 to 26 W?
a. 2
b. 3
c. -3
d. 6
