Showing posts with label MCQs. Show all posts
Showing posts with label MCQs. Show all posts

Basic Electrical Engineering MCQs #SET1

01) Two 100W, 200V lamps are connected in series across a 200V supply. The total power consumed by each lamp will be in Watts :-
A) 25 Watts
B) 50 Watts
C) 100 Watts
D) 200 Watts

02) Two electric bulbs have transparent filament of same thickness. It one of them gives 60 W & other gives 100 W, then-
A) 60 W lamp filament has shorter length
B) 100 W lamp filament has longer length
C) 60 W lamp filament has longer length
D) 60 W & 100 W lamp filament have equal length

03) Bulb in street lighting are connected in
A) Parallel
B) Series
C) Series parallel
D) end of end

04) A piece of copper and another piece of germanium are cooled from room temperature to 80K. The resistance of
A) each of them increases.
B) each of them decreases.
C) copper increases and germanium decreases.
D) copper decreases and germanium increases.

05) If a large resistance is connected parallel a small resistance then net resistance will be
A) Greater than the large resistance
B) Smaller than the small resistance
C) Smaller than the greater but larger than the smaller resistance
D) None of the above option

06) The speed of a DC motor is
A) Directly proportional to flux and inversely proportional to back emf.
B) Directly proportional to both back emf and flux.
C) Directly proportional to back emf and flux.
D) Directly proportional to back emf and inversely proportional flux.

07) In which braking back emf exceeds supply voltage?
A) Regenerative.
B) Dynamic.
C) Plugging.
D) None of these.

08) Third pin of a 3 pin plug is thicker and longer due to
A) for designing purpose.
B) for protection purpose.
C) all pins are of same size.
D) none of these.

09) Power factor can be defined as
A) both option B and C.
B) cosine of angle between voltage and current.
C) ratio of resistance versus impedance.
D) sine of voltage and current.

10)A 60 Hz frequency voltage would case a bulb to turn on and off
A) 60 times per second.
B) 120 times per second.
C) 70 times per second.
D) 80 times per second.


Semiconductor Diode MCQs Questions & Answers

In this post composed with  Electrical Interview Questions,Answers On Semiconductor Diode  MCQs Questions,Answers On  Semiconductor Diode which are asked in most of the interviews and competitive exams like GATE (India),PGCET..etc.

Electrical Interview Questions On Semiconductor Diode

1. A crystal diode has ........

(i) one pn junction
(ii) two pn junctions
(iii) three pn junctions
(iv) none of the above

2. A crystal diode has forward resistance of the order of ........

(i) kΩ
(ii) Ω
(iii) MΩ
(iv) none of the above

3. If the arrow of crystal diode symbol is positive w.r.t. bar, then diode is ........ biased.

(i) forward
(ii) reverse
(iii) either forward or reverse
(iv) none of the above

4. The reverse current in a diode is of the order of ........

(i) kA 
(ii) mA
(iii) μA 
(iv) A

5. The forward voltage drop across a silicon diode is about ........

(i) 2.5 V 
(ii) 3 V
(iii) 10 V 
(iv) 0.7 V

6. A crystal diode is used as ........

(i) an amplifier 
(ii) a rectifier
(iii) an oscillator 
(iv) a voltage regulator

7. The d.c. resistance of a crystal diode is ........ its a.c. resistance.

(i) the same as
(ii) more than
(iii) less than
(iv) none of the above

8. An ideal crystal diode is one which behaves as a perfect ........ when forward biased.

(i) conductor

(ii) insulator
(iii) resistance material
(iv) none of the above

9. The ratio of reverse resistance and forward resistance of a germanium crystal diode is about ........

(i) 1 : 1 
(ii) 100 : 1
(iii) 1000 : 1 
(iv) 40000 : 1

10. The leakage current in a crystal diode is due to ........

(i) minority carriers
(ii) majority carriers
(iii) junction capacitance
(iv) none of the above

11. If the temperature of a crystal diode increases,then leakage current ........

(i) remains the same
(ii) decreases
(iii) increases
(iv) becomes zero

12. The PIV rating of a crystal diode is ........ that of equivalent vacuum diode.

(i) the same as 
(ii) lower than
(iii) more than 
(iv) none of the above

13. If the doping level of a crystal diode is increased,the breakdown voltage .........

(i) remains the same
(ii) is increased
(iii) is decreased
(iv) none of the above

14. The knee voltage of a crystal diode is approximately equal to ........

(i) applied voltage
(ii) breakdown voltage
(iii) forward voltage
(iv) barrier potential

15. When the graph between current through and voltage across a device is a straight line, the device is referred to as ........

(i) linear 
(ii) active
(iii) nonlinear 
(iv) passive

16. When the crystal diode current is large, the bias is ........

(i) forward 
(ii) inverse
(iii) poor 
(iv) reverse

17. A crystal diode is a ........ device.

(i) non-linear 
(ii) bilateral
(iii) linear 
(iv) none of the above

18. A crystal diode utilities ........ characteristic for rectification.

(i) reverse 
(ii) forward
(iii) forward or reverse
(iv) none of the above

19. When a crystal diode is used as a rectifier, the most important consideration is ........

(i) forward characteristic
(ii) doping level
(iii) reverse characteristic
(iv) PIV rating

20. If the doping level in a crystal diode is increased, the width of depletion layer ........

(i) remains the same
(ii) is decreased
(iii) is increased
(iv) none of the above

21. A zener diode has ........

(i) one pn junction
(ii) two pn junctions
(iii) three pn junctions
(iv) none of the above

22. A zener diode is used as ........

(i) an amplifier 
(ii) a voltage regulator
(iii) a rectifier 
(iv) a multivibrator

23. The doping level in a zener diode is ........ that of a crystal diode.

(i) the same as 
(ii) less than
(iii) more than 
(iv) none of the above

24. A zener diode is always .......... connected.

(i) reverse
(ii) forward
(iii) either reverse or forward
(iv) none of the above

25. A zener diode utilises ........ characteristic for its operation.

(i) forward
(ii) reverse
(iii) both forward and reverse
(iv) none of the above

26. In the breakdown region, a zener diode behaves like a ......... source.

(i) constant voltage
(ii) constant current
(iii) constant resistance
(iv) none of the above

27. A zener diode is destroyed if it ........

(i) is forward biased
(ii) is reverse biased
(iii) carries more than rated current
(iv) none of the above

28. A series resistance is connected in the zener circuit to ........

(i) properly reverse bias the zener
(ii) protect the zener
(iii) properly forward bias the zener
(iv) none of the above

29. A zener diode is ........ device.

(i) a non-linear 
(ii) a linear
(iii) an amplifying 
(iv) none of the above

30. A zener diode has ........ breakdown voltage.

(i) undefined 
(ii) sharp
(iii) zero 
(iv) none of the above

31. ........ rectifier has the lowest forward resistance.

(i) solid state 
(ii) vacuum tube
(iii) gas tube 
(iv) none of the above

32. Mains a.c. power is converted into d.c. power for ........

(i) lighting purposes
(ii) heaters
(iii) using in electronic equipment
(iv) none of the above

33. The disadvantage of a half-wave rectifier is that the ........

(i) components are expensive
(ii) diodes must have a higher power rating
(iii) output is difficult to filter
(iv) none of the above

34. If the a.c. input to a half-wave rectifier has an r.m.s. value of 400/√2 volts, then diode PIV rating is ........

(i) 400/√2 V 
(ii) 400 V
(iii) 400 ×√2 V 
(iv) none of the above

35. The ripple factor of a half-wave rectifier is ........

(i) 2 
(ii) 1.21
(iii) 2.5 
(iv) 0.48

36. There is a need of transformer for ........

(i) half-wave rectifier
(ii) centre-tap full-wave rectifier
(iii) bridge full-wave rectifier
(iv) none of the above

37. The PIV rating of each diode in a bridge rectifier is ........ that of the equivalent centretap rectifier.

(i) one-half 
(ii) the same as
(iii) twice 
(iv) four times

38. For the same secondary voltage, the output voltage from a center-tap rectifier is ........ than that of bridge rectifier.

(i) twice 
(ii) thrice
(iii) four times 
(iv) one-half

39. If the PIV rating of a diode is exceeded, ........

(i) the diode conducts poorly
(ii) the diode is destroyed
(iii) the diode behaves as zener diode
(iv) none of the above

40. A 10 V power supply would use ........ as filter capacitor.

(i) paper capacitor 
(ii) mica capacitor
(iii) electrolytic capacitor
(iv) air capacitor

41. A 1000 V power supply would use ........ as a filter capacitor.

(i) paper capacitor
(ii) air capacitor
(iii) mica capacitor
(iv) electrolytic capacitor

42. The ...... filter circuit results in the best voltage regulation.

(i) choke input
(ii) capacitor input
(iii) resistance input
(iv) none of the above

43. A half-wave rectifier has an input voltage of 240 V r.m.s. If the step-down transformer has a turns ratio of 8 : 1, what is the peak load voltage ? Ignore diode drop.

(i) 27.5 V 
(ii) 86.5 V
(iii) 30 V 
(iv) 42.5 V

44. The maximum efficiency of a half-wave rectifier is ...........

(i) 40.6% 
(ii) 81.2%
(iii) 50% 
(iv) 25%

45. The most widely used rectifier is ...........

(i) half-wave rectifier
(ii) centre-tap full-wave rectifier
(iii) bridge full-wave rectifier
(iv) none of the above


EEIQS 3- Electrical Interview Question On Transmission and Distribution

Here we have Electrical Interview Questions On A.C. Transmission and Distribution ,MCQs On Power Electronics which are asked in most of the interviews and competitive exams like GATE (India),PGCET..etc.

Interview Question,Objectives on A.C. Transmission and Distribution:

Q1.With same maximum voltage between conductors, the ratio of copper volumes in 3-phase, 3- wire system and 1-phase, 2-wire system is
(a) 4/3
(b) 3/4
(c) 5/3
(d) 3/5

Q2. The volume of copper required for an a.c. transmission line is inversely proportional to
(a) current
(b) voltage
(c) power factor
(d) both (b) and (c)
(e) both (a) and (c).

Q3. For a.c. transmission lines less than 80 km in length, it is usual to lump the line capacitance at
(a) the receiving end
(b) the sending end
(c) the mid-point
(d) any convenient point.

Q4. Corona occurs between two transmission wires when they
(a) are closely-spaced
(b) are widely-spaced
(c) have high potential difference
(d) carry d.c. power.

Q5. The only advantage of corona is that it
(a) makes line current non-sinusoidal
(b) works as a safety-valve for surges
(c) betrays its presence by hissing sound
(d) produces a pleasing luminous glow.

Q6. The sag produced in the conductor of a transmission wire depends on
(a) weight of the conductor per unit length
(b) tension in the conductor
(c) length of the conductor
(d) all of the above
(e) none of the above.

Q7. Suspension insulators are used when transmission voltage is
(a) high
(b) low
(c) fluctuating
(d) steady

Q8. The string efficiency of suspension insulators can be increased by
(a) providing a guard ring
(b) grading the insulators
(c) using identical insulator disc
(d) both (a) & (b).

Q9. An interconnector between two generating stations facilitates to
(a) keep their voltage constant
(b) run them in parallel
(c) transfer power in either direction
(d) both (b) & (c)

Q10. The effective disruptive critical voltage of a transmission line does NOT depend on
(a) irregularity factor
(b) conductor radius
(c) distance between conductors
(d) material of the conductors.

Q11. By which of the following systems electric power may be transmitted?
(a) Overhead system
(b) Underground system
(c) Both (a) and (b)
(d) None of the above

Q12. ....... are the conductors, which cannect the consumer's terminals to the distribution
(a) Distributors
(b) Service mains
(c) Feeders
(d) None of the above

Q13. The underground system cannot be operatedabove
(a) 440 V
(b) 11 kV
(c) 33 kV
(d) 66 kV

Q14. Overhead system can be designed for operation upto
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 400 kV

Q15. If variable part of annual cost on account of interest and depreciation on the capital outlay is equal to the annual cost of electrical energy wasted in the conductors, the total annual cost will be minimum and the corresponding size of conductor will be most economical. This statement is known as
(a) Kelvin's law
(b) Ohm's law
(c) Kirchhoff's law
(d) Faraday's law
(e) none of the above

Q16. The wooden poles well impregnated with creosite oil or any preservative compound have life
(a) from 2 to 5 years
(b) 10 to 15 years
(c) 25 to 30 years
(d) 60 to 70 years

Q17. Which of the following materials is not used for transmission and distribution of electrical power?
(a) Copper
(b) Aluminium
(c) Steel
(d) Tungsten

Q18. Galvanised steel wire is generally used as
(a) stay wire
(b) earth wire
(c) structural components
(d) all of the above

Q19. The usual spans with R.C.C. poles are
(a) 40–50 metres
(b) 60–100 metres
(c) 80–100 metres
(d) 300–500 metres

Q20. The corona is considerably affected by which of the following?
(a) Size of the conductor
(b) Shape of the conductor
(c) Surface condition of the conductor
(d) All of the above

We hope you enjoyed an objective test on  A.C. Transmission and Distribution ,this is the collection of latest electrical interview,competitive exam questions,MCQs.

EEIQS 2- Electrical Interview Question On DC Machines

It is a collection of most frequently asked  Interview Question On DC Machines in various examinations like GATE,DRDO,BARC...etc.
Electrical Questions from DC Motors,generators.Write an online test on latest Interview questions,Interview preparation.
Here You Get Important Electrical Interview Objective Questions ,MCQswith Answers

Electrical Machines - DC Machines Objectives,MCQs:

[Q-1]The basic requirement of a d.c. armature winding is that it must be
(a) a closed one 
(b) a lap winding
(c) a wave winding
(d) either (b) or (c)

[Q-2]The sole purpose of a commutator in a dc generator is to
(a) Increase output voltage
(b) Reduce sparking at brushes
(c) Provide smoother output
(d) Convert the induced ac into dc
(e) None of the above.

[Q-3] The voltage regulation of an over compound dc generator is always
(a) Positive
(b) Negative
(c) Zero
(d) High

[Q-4] A wave winding must go at least ............ around the armature before it closes back where it started.
(a) once
(b) twice
(c) thrice
(d) four times

[Q-5] In small DC machines, armature slots are sometimes not made axial but are skewed, results in
(a) Quieter operation
(b) Slight decrease in losses
(c) Saving of copper
(d) Both a and b
(e) None of the above
Ans: Protects from magnetic locking.

[Q-6]The d.c. armature winding in which coil sides are a pole pitch apart is called ............ winding.
(a) multiplex
(b) fractional-pitch
(c) full-pitch
(d) pole-pitch

[Q-7]For making coil span equal to a pole pitch in the armature winding of a d.c. generator, the back pitch of the winding must equal the number of
(a) commutator bars per pole
(b) winding elements
(c) armature conductors per path
(d) armature parallel paths.

[Q-8]The critical resistance of the dc generator is the resistance of
(a) Armature
(b) Field
(c) Load
(d) Brushes
(e) None of the above.

[Q-9]The primary reason for making the coil span of a d.c. armature winding equal to a pole pitch is to
(a) obtain a coil span of 180º (electrical)
(b) ensure the addition of e.m.fs. of consecutive turns
(c) distribute the winding uniformly under different poles
(d) obtain a full-pitch winding.

[Q-10]In a 4-pole, 35 slot d.c. armature, 180 electrical-degree coil span will be obtained when coils occupy ............ slots.
(a) 1 and 10
(b) 1 and 9
(c) 2 and 11
(d) 3 and 12

[Q-11]For standing a DC motor a starter is required because
(a)it limits the starting current to a safe value. 
(b)It starts the motor.
(c)it limits the speed of the motor. 
(d)None of the above.

[Q-12]When two DC series motors are connected in parallel, the resultant speed is 
(b)Normal speed. 
(c)Less than normal speed. 
(d)More than normal speed.

[Q-13]To get the speed of DC motor is more than normal without wastage of electrical energy _____________ is used.
(a)Rheostatic control.
(b)Ward Leonard control.
(c)Any of above method.
(d)None of above.

[Q-14]The armature of a d.c. generator has a 2-layer lap-winding housed in 72 slots with six conductors/slot. What is the minimum number of commutator bars required for the armature?
(a) 72
(b) 432
(c) 216
(d) 36

[Q-15]The sole purpose of a commutator in a d.c. Generator is to
(a) increase output voltage
(b) reduce sparking at brushes
(c) provide smoother output
(d) convert the induced a.c. into d.c.

[Q-16]In a dc generator, the generator, the generated emf is directly proportional to the
(a) Field current
(b) Pole flux
(c) Number of armature parallel paths
(d) Number of dummy coils
(e) None of the above

[Q-17]For a 4-pole, 2-layer, d.c., lap-winding with 20 slots and one conductor per layer, the number of commutator bars is
(a) 80
(b) 20
(c) 40
(d) 160

[Q-18]A 4-pole, 12-slot lap-wound d.c. armature has two coil-sides/slot. Assuming single turn coils and progressive winding, the back pitch would be
(a) 5
(b) 7
(c) 3
(d) 6

[Q-19]A DC shunt motor is operating at no load. If the armature is shunted by a resistance, its speed will
(c)Remain the same. 
(d)Be unpredictable.

[Q-20]The armature voltage control is considered suitable for a DC motor driven at constant

[Q-21]If in the case of a certain d.c. armature, the number of commutator segments is found either one less or more than the number of slots, the armature must be having a simplex ............ winding.
(a) wave
(b) lap
(c) frog leg
(d) multi element.

[Q-22]Lap winding is suitable for ............ current,............ voltage d.c. generators.
(a) high, low
(b) low, high
(c) low, low
(d) high, high.

[Q-23]The essential condition for stable parallel operation of two dc generators having similar characteristics is that they should have
(a) Same kilowatt output ratings
(b) Dropping voltage characteristics
(c) Same percentage regulation
(d) Same no load and full load speed
(e) None of the above

[Q-24]An ideal dc generator has .......... voltage regulation.
(a) Low
(b) Zero
(c) Positive
(d) Negative
(e) None of the above

[Q-25]Which generator has poorest voltage regulation
(a) Series
(b) Compound
(c) Shunt
(d) High
(e) None of the above


EEIQS 1- Electrical Interview Questions On Power Electronics MCQs

It is the smartest collection of Electrical Interview Questions On  Power Electronics ,MCQs On Power Electronics which are asked in most of the interviews and competitive exams like GATE (India),PGCET..etc.

Power Electronics Interview Questions:-

[Q-1]What is latching current?
[A]It is defined as minimum value of anode current which it must attain during turn on process to maintain conduction when gate signal is removed.

[Q-2]What is holding current?
[A]It is defined as minimum value of anode current below which the SCR gets turned off.

[Q-3]What is AC voltage controller?
[A]It is defined as the power electronics converter which converts the fixed AC voltage into a variable AC voltage without change in the frequency.

[Q-4] What are the different turn on methods of SCR?
[A]Forward voltage triggering,Gate Triggering,dv/dt triggering,Temperature triggering,Light triggering

[Q-5]What is spread time of SCR?
[A]The time taken by anode current to reach from 0.9Ia to Ia.

[Q-6] What is meant by SOA of SCR?

[A]SOA – Safe Operating Area determines the voltage and current boundary within which the Power Device can be operated without destructive failure.

[Q-7] What is chopper?

[A] Chopper is a power electronics circuit which converts fixed value of DC to variable DC output.

Frequently asked Power Electronics interview questions

[Q-8] What is meant by commutation?
[A]The process of changing the polarity of the voltage across the terminals of SCR is called commutation.
Simply turing off process of SCR 

[Q-9]what is the turn off time of half converter with R load?
[A] T= π/ ω;
 where ω=2πf
π in rad

[Q-10]What is forced commutation?
[A]The process of the reversal of current through thyristor(SCR) by an external circuit is called forced commutation.

[Q-11] What is meant by cyclo-converter?
[A]cyclo-converter is a power electronic circuit which converts AC power at one frequency to other frequency.

[Q-12] What is firing angle?
firing angle defined as the angle measured from the instant SCR gets forward biased to the instant it is triggered.

[Q-13] Silicon based rectifiers are preferred than germanium based rectifiers because

(a) Si is available easily compared to Ge
(b) Only Si has a stable off state
(c) Ge is very temperature sensitive
(d) Si only has the characteristics α1 + α2 < 1 at low collector currents and reaches 1 at high currents
Which of the above statements are true?
1. A, B, D
2. B, D
3. B Only
4. D Only

[A] 2

[Q-14] What is step down cyclo-converter?
[A]It is the converter whose output frequency is less than the input frequency.

[Q-15] What is step up cyclo-converter ?
[A]It is the converter whose output frequency is more than the input frequency.

[Q-16] What is duty cycle of a chopper?
[A]It is the ratio of the ON time of the chopper to total time period of the chopper.
D = Ton / [Ton + Toff]

[Q-17]SCR based converter,what is the use of free wheeling diode?
[A]Conduct current during the OFF period of the SCR and to reduce negetive peak voltage in RL & RLE loads.

[Q-18] What is meant by pulse triggered devices?
[A]As the name indicates, to trigger these devices just a pulse is sufficient. Continuous gate voltage of entire on time is not required. The advantage of pulse triggering is, it will avoid the hard triggering.
Ex. Thyristor, GTO

[Q-19] " Six MOSFETs connected in a bridge configuration (having no other power device) MUST be operated as a Voltage Source Inverter (VSI) ". This statement is 
A. True, because being majority carrier devices, MOSFETs are voltage driven
B. True, because MOSFETs have inherently anti parallel diodes
C. False, because it can be operated both as current source Inverter (CSI) or a VSI
D. False, because MOSFETs can be operated as excellent constant current sources in the saturation region.

[A] D

[Q-20] What is meant by GTO?
[A]GTO-gate turn off thyristor It is a three terminal, four layer PNPN  Power Semiconductor device that can be turned on by a positive gate current and can be turned off by a reverse gate current.

[Q-21] What does 10V AC mean? Is it the RMS voltage or Peak voltage or Average voltage?
[A]In general,  AC voltages and currents are mentioned in RMS values only. It is sensible to compare with steady DC voltages and currents.
For example 230V AC supply means, 230Vrms AC Supply.

[Q-22] When we have to connect the SCRs in a parallel manner?
[A]To meet the high current demand we will connect the SCRs in a parallel manner.Similarly to meet the high voltage demand we have to connect the SCRs in series.

[Q-23] What is AC voltage controller?
It is defined as the power electronics converter which converts the fixed AC voltage into a variable AC voltage without change in the frequency.

[Q-24] What is inverter? What are the types of Inverter?
[A]A device which converts dc power into ac power at desired output voltage and frequency is called as Inverter.
Inverters are broadly classified into
Voltage Source Inverter (VSI)
Current Source Inverter (CSI)

[Q-25]Circuit turn-off time of an SCR is defined as the time 
A. Taken by the SCR to turn off
B. Required for SCR current to become zero
C. For which the SCR is reverse biased by the commutation circuit
D. For which the SCR is reverse biased to reduce its current below the holding current


Above we shared some basic interview question on power electronics for electrical engineers.