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Rites ltd electronics questions with answers for practice
Rites Ltd electronics
Q.1 The two windings of a transformer is
(A) conductively linked.
(B) inductively linked.
(C) not linked at all.
(D) electrically linked.
Ans : B
Q.2 A salient pole synchronous motor is running at no load. Its field current is switched off. The motor will
(A) come to stop.
(B) continue to run at synchronous speed.
(C) continue to run at a speed slightly more than the synchronous speed.
(D) continue to run at a speed slightly less than the synchronous speed.
Ans: B
Q.3 The d.c. series motor should always be started with load because
(A) at no load, it will rotate at dangerously high speed.
(B) it will fail to start.
(C) it will not develop high starting torque.
(D) all are true.
Ans: A
Q.4 The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full load speed is about
(A) 50 Hz.
(B) 20 Hz.
(C) 2 Hz.
(D) Zero.
Ans: C
Q.5 In a stepper motor the angular displacement
(A) can be precisely controlled.
(B) it cannot be readily interfaced with micro computer based controller.
(C) the angular displacement cannot be precisely controlled.
(D) it cannot be used for positioning of work tables and tools in NC machines.
Ans: A
Q.6 The power factor of a squirrel cage induction motor is
(A) low at light load only.
(B) low at heavy load only.
(C) low at light and heavy load both.
(D) low at rated load only.
Ans: A
Q.7 The generation voltage is usually
(A) between 11 KV and 33 KV.
(B) between 132 KV and 400 KV.
(C) between 400 KV and 700 KV.
(D) None of the above.
Ans: A
Q.8 When a synchronous motor is running at synchronous speed, the damper winding produces
(A) damping torque.
(B) eddy current torque.
(C) torque aiding the developed torque.
(D) no torque.
Ans: D
Q.9 If a transformer primary is energised from a square wave voltage source, its output voltage will be
(A) A square wave.
(B) A sine wave.
(C) A triangular wave.
(D) A pulse wave.
Ans: A
Q.10 In a d.c. series motor the electromagnetic torque developed is proportional to
Option figure
Ans: B
Q.11 In a 3 – phase induction motor running at slip ‘s’ the mechanical power developed in terms of air gap power
11 and 12 figure
In a 3 – phase induction motor the maximum torque
(A) is proportional to rotor resistance
(B) does not depend on
(C) is proportional to
(D) is proportional to
Q.13In a d.c. machine, the armature mmf is
(A) stationary w.r.t. armature.
(B) rotating w.r.t. field.
(C) stationary w.r.t. field.
(D) rotating w.r.t. brushes.
Ans: C
Q.14In a transformer the voltage regulation will be zero when it operates at
(A) unity p.f.
(B) leading p.f.
(C) lagging p.f.
(D) zero p.f. leading.
Ans: B
Q.15 The maximum power in cylindrical and salient pole machines is obtained respectively at load angles of
Q.16 The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be
(A) 3.6 V.
(B) 2.5 V.
(C) 3.0 V.
(D) 6.0 V.
Ans: C
Q.17 The emf induced in the primary of a transformer
(A) is in phase with the flux.
(B) lags behind the flux by 90 degree.
(C) leads the flux by 90 degree.
(D) is in phase opposition to that of flux.
Ans: C
Q.18 The relative speed between the magnetic fields of stator and rotor under steady state operation is zero for a
(A) dc machine.
(B) 3 phase induction machine.
(C) synchronous machine.
(D) single phase induction machine.
Ans: all options are correct
Q.19 The current from the stator of an alternator is taken out to the external load circuit through
(A) slip rings.
(B) commutator segments.
(C) solid connections.
(D) carbon brushes.
Ans: C
Q.20 A motor which can conveniently be operated at lagging as well as leading power factors is the
(A) squirrel cage induction motor.
(B) wound rotor induction motor.
(C) synchronous motor.
(D) DC shunt motor.
Ans: C
Q.21 A hysteresis motor
(A) is not a self-starting motor.
(B) is a constant speed motor.
(C) needs dc excitation.
(D) can not be run in reverse speed.
Ans: B
Q.22
The most suitable servomotor for low power applications is
(A) a dc series motor.
(B) a dc shunt motor.
(C) an ac two-phase induction motor.
(D) an ac series motor.
Ans: B
Q.23 The size of a conductor used in power cables depends on the
(A) operating voltage.
(B) power factor.
(C) current to be carried.
(D) type of insulation used.
Ans: C
Q.24 Out of the following methods of heating the one which is independent of supply frequency is
(A) electric arc heating
(B) induction heating
(C) electric resistance heating
(D) dielectric heating
Ans: C
Q.25
A two-winding single phase transformer has a voltage regulation of 4.5% at full-load and unity power-factor. At full-load and 0.80 power-factor lagging load the voltage regulation will be
(A) 4.5%.
(B) less than 4.5%.
(C) more than 4.5%.
(D) 4.5% or more than 4.5%.
Ans: C
Electronics Quiz
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-Answer
.
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-Answer
Both anodes will not conduct
None of these
.
4. Ripple frequency of full wave rectifier working on 50 Hz supply will be
25 Hz-Answer
150 Hz
6 anode rectifier with inter phase transformer
All will have identical power factor
.
5. The form factor for half-wave rectifier sine wave is
1.05
1.15
1.45
1.57-Answer
6. A silicon controlled rectifier is a
Unijuction device
Device with three junctions-Answer
Device with four junctions
None of the above
.
7. For full-wave rectifier sine wave, form factor is
1.55
1.44
1.22
1.11-Answer
.
8. At absolute zero temperature a semi-conductor behaves as
An Insulator-Answer
A Super-Conductor
A Good Conductor
A Variable Resistor
.
9. An electron in the conduction band
Has higher energy than the electron in the valence band-Answer
Has lower energy than the electron in the valence band
Loses its charge easily
Jumps to the top of the crystal
.
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-Answer
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
.
11. Before doping semiconductor material is generally
Dehydrated
Heated
Hardened
Purified-Answer
.
12. Select the one that is a acceptor impurity element
Antimony
Gallium-Answer
Arsenic
Phosphorous
.
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-Answer
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-Answer
When forward bias exceeds a certain value
When forward current exceeds a certain value
.
15. Select the rectifier that needs four diodes
Half wave rectifier
Center-tap full wave rectifier
Bridge rectifier-Answer
None of the above
.
16. Maximum forward current in case of signal diode is in the range of
1A to 10A
0.1A to 1A
Few milli amperes-Answer
Few nano amperes
.
17. In a semiconductor avalanche breakdown takes place when
Reverse bias exceeds the limiting value-Answer
Forward bias exceeds the limiting value
Forward current exceeds the limiting value
Potential barrier is reduced to zero
.
18. The D.C output voltage from a power supply
Increases with higher values of filter capacitance and decreases with more load current-Answer
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
.
19. A solar cell provides a example of
Photo Voltaic Cell-Answer
Photo Conductive Cell
Photo Emissive Cell
Photo Radiation 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-Answer
Hotons are emitted
Electrons of higher energy are emitted
Electrons of lower energy 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-Answer
Infinitely large resistance in reverse bias
Infinitely large resistance in forward as well as 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-Answer
Is given by forward voltage / reverse leakage current
.
23. In which case the temperature coefficient is positive
Intrinsic Semi-Conductor
Extrinsic Semi-Conductor-Answer
Both intrinsic as well as extrinsic semi-conductor
Neither intrinsic nor extrinsic semi-conductor
.
24. A PNP transistor is generally made of
Silicon
Germanium
Either silicon or germanium-Answer
None of the above
.
25. In a transistor the region that is very lightly doped and is very thin is
Emitter
Base-Answer
Collector
None of these
.
26. In a NPN transitor, when emitter junction is forward biased and collector junction is reverse biased, the transistor will operate in
Active Region-Answer
Saturated Region
Cut of Region
Inverted 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-Answer
Emitter junction as well as collector junction are forward biased
Emitter junction as well as collector junction are reverse 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-Answer
The base region must be made of some insulating material
The collector region must be heavily doped
.
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-Answer
Some D.C voltage is applied in the forward direction to the emitter junction with the collector open circuited
.
30. The current Icbo
Increases with increase in temperature-Answer
Is normally greater for silicon transistors than germanium transistors
Mainly depends on the emitter base junction
Depends largely on the emitter doping
.
31. Thermal runway of a transitor occurs when
Heat dissipation from transistor is excessive
Transistor joints melt due to high temperature
There is excessive leakage current due to temperature rise-Answer
None of above
.
