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HPC Elec engg questions
1. In a mercury arc rectifier
Ion stream moves from cathode to anode
Current flows from cathode to anode
Electron stream moves form anode to cathode
Ion stream moves from anode to cathode
The answer is Ion stream moves from anode to cathode
2. For producing cathode spot in a mercury arc rectifier
An auxiliary electrode is used
Tube is evacuated
Low mercury vapour pressures are used
Anode is heated
.The answer is Anode is heated
3. If the voltage of anode B is raised to 510 V
Anode B will conduct but anode A will also continue to conduct
Anode B will not conduct but anode A will continue to conduct
Both anodes will not conduct
None of these
.
The answer is Anode B will conduct but anode A will also continue to conduct
4. Ripple frequency of full wave rectifier working on 50 Hz supply will be
25 Hz
150 Hz
6 anode rectifier with inter phase transformer
All will have identical power factor
.
The answer is 25 Hz
5. The form factor for half-wave rectifier sine wave is
1.05
1.15
1.45
1.57
.
The answer is 1.57
6. A silicon controlled rectifier is a
Unijuction device
Device with three junctions
Device with four junctions
None of the above
The answer is Device with three junctions
7. For full-wave rectifier sine wave, form factor is
1.55
1.44
1.22
1.11
The answer is 1.11
8. At absolute zero temperature a semi-conductor behaves as
An Insulator
A Super-Conductor
A Good Conductor
A Variable Resistor
The answer is An Insulator
9. An electron in the conduction band
Has higher energy than the electron in the valence band
Has lower energy than the electron in the valence band
Loses its charge easily
Jumps to the top of the crystal
The answer is Has higher energy than the electron in the valence band
10. EG for silicon is 1.12 eV and for germanium is 0.72 eV thus it can be conducted that
More number of electron-hole pairs will be generated in silicon than in germanium at room temperature
Less number of electron hole pairs will be generated in silicon than in germanium at room temperature
Equal number of electron hole pairs will be generated in both at lower temperatures
Equal number of electron hole pairs will be generated in both at higher temperatures
.The answer is Less number of electron hole pairs will be generated in silicon than in germanium at room temperature
11. Before doping semiconductor material is generally
Dehydrated
Heated
Hardened
Purified
.The answer is Purified
12. Select the one that is a acceptor impurity element
Antimony
Gallium
Arsenic
Phosphorous
.The answer is GalliumThe answer is Electrons move towards positive terminal and holes towards negative terminal
13. At room temperature when a voltage is applied to an intrinsic semiconductor
Most of the electrons and holes move towards negative terminal
Most of the electrons and holes move towards positive terminal
Electrons move towards positive terminal and holes towards negative terminal
The answer is Electrons move towards negative terminal and holes towards positive terminal
.
14. Under which of the following conditions avalanche breakdown in a semiconductor diode takes place ?
When potential barrier is reduced to zero
When reverse bias exceeds a certain value
When forward bias exceeds a certain value
When forward current exceeds a certain value
.The answer is When reverse bias exceeds a certain value
15. Select the rectifier that needs four diodes
Half wave rectifier
Center-tap full wave rectifier
Bridge rectifier
None of the above
.
The answer is Bridge rectifier
16. Maximum forward current in case of signal diode is in the range of
1A to 10A
0.1A to 1A
Few milli amperes
Few nano amperes
.The answer is Few milli amperes
17. In a semiconductor avalanche breakdown takes place when
Reverse bias exceeds the limiting value
Forward bias exceeds the limiting value
Forward current exceeds the limiting value
Potential barrier is reduced to zero
.The answer is Reverse bias exceeds the limiting value
18. The D.C output voltage from a power supply
Increases with higher values of filter capacitance and decreases with more load current
Decreases with higher values of filter capacitance and increases with more load current
Decreases with higher values of filter capacitance as well as with more load current
Increases with higher values of filter capacitance as well as with more load current
.The answer is Increases with higher values of filter capacitance and decreases with more load current
19. A solar cell provides a example of
Photo Voltaic Cell
Photo Conductive Cell
Photo Emissive Cell
Photo Radiation Cell
.The answer is Photo Voltaic Cell
20. When yellow light is incident on a surface, no electrons are emitted while green light can emit. If red light is incident on the surface, then it is expected that
No electrons are emitted
Hotons are emitted
Electrons of higher energy are emitted
Electrons of lower energy are emitted
.The answer is No electrons are emitted
21. An ideal diode should have
Zero resistance in the forward bias as well as reverse bias
Zero resistance in the forward bias and an infinitely large resistance in reverse bais
Infinitely large resistance in reverse bias
Infinitely large resistance in forward as well as reverse bais
.The answer is Zero resistance in the forward bias and an infinitely large resistance in reverse bais
22. The reverse resistance of a PN juction diode
Is always low
Is always high
Is given by breakdown voltage / reverse leakage current
Is given by forward voltage / reverse leakage current
.The answer is Is given by breakdown voltage / reverse leakage current
23. In which case the temperature coefficient is positive
Intrinsic Semi-Conductor
Extrinsic Semi-Conductor
Both intrinsic as well as extrinsic semi-conductor
Neither intrinsic nor extrinsic semi-conductor
.The answer is Extrinsic Semi-Conductor
24. A PNP transistor is generally made of
Silicon
Germanium
Either silicon or germanium
None of the above
.The answer is Either silicon or germanium
25. In a transistor the region that is very lightly doped and is very thin is
Emitter
Base
Collector
None of these
.The answer is Base
26. In a NPN transitor, when emitter junction is forward biased and collector junction is reverse biased, the transistor will operate in
Active Region
Saturated Region
Cut of Region
Inverted Region
.The answer is Active Region
27. A transistor will operate in inverted region if
Emitter junction is forward biased and collector junction is reverse biased
Emitter junction is reverse biased and collector junction is forward biased
Emitter junction as well as collector junction are forward biased
Emitter junction as well as collector junction are reverse biased
.The answer is Emitter junction is reverse biased and collector junction is forward biased
28. Which of the following is essential for transistor action ?
The base region must be very wide
The base region must be very narrow
The base region must be made of some insulating material
The collector region must be heavily doped
.The answer is The base region must be very narrow
29. In a transistor, current ICBO flows when
Some D.C voltage is applied in the reverse direction to the emitter junction with the collector open circuited
Some D.C voltage is applied in the forward direction to the collector junction with the emitter open circuited
Some D.C voltage is applied in the reverse direction to the collector junction with the emitter open circuited
Some D.C voltage is applied in the forward direction to the emitter junction with the collector open circuited
.
The answer is Some D.C voltage is applied in the reverse direction to the collector junction with the emitter open circuited
30. The current Icbo
Increases with increase in temperature
Is normally greater for silicon transistors than germanium transistors
Mainly depends on the emitter base junction
Depends largely on the emitter doping
The answer is Increases with increase in temperature
