National Thermal Power Corporation Question-Bank Contributed by Dymi Paul updated on Mar 2019

 

NTPC Diploma Engineer Trainees (Mechanical/Electrical/Control and Instrumentation) Model Technical Questions

 

Section A. Control and Instrumentation


1. Air-cored inductors are used for low frequency/high frequency/equal frequency operations.

 

2. Inverse laplace transform of 1/s2[d/ds(e-3s/s)]

 

3. When I mode is added to proportional control system stability increases/ decreases/ steady state performance deteriorates/damping increases.


4. Given 4 pole-zero plots identify which one corresponds to the driving point impedance of a series resonant ckt.

 

5. Given four unit-circle plots identify the one corresponding to a bandpass filter.

 

6. Expression for ?

 

(n): u(n)-u(n-1)/ u(n-1)-u(n+1)/ u(n)+u(n+1)/…

 

7. Numerical on a photodiode: to calculate the responsivity/sensitivity when a specified no of incident photons cause a specified no of electron generation.


8. Lower useful input limit of a transducer is determined by


9. The sequence (2,3,4,3) is circularly even/circularly odd/circularly zero/both circularly even and odd.

 

10. Given a circuit with a 50 ? resistor in series between two voltage sources of 10 V and 5 V magnitude calculate the power delivered by 5 V source.

 

11. Laplace transform of e-3tu(t)+e2tu(-t).

 

12. Which photodetector has output affected by own intrinsic noise: PN/APD/PIN/all.


13. Match the following with their characteristics: LED/LCD/nixie tube/optical fibre.

 

14. A 4 kHz signal is sampled at thrice the Nyquist rate and sent through a channel with error ?1%. Calculate the bandwidth of the channel.

 

15. Given an op-amp ckt obtain an expression for o/p voltage.

 

16. No. of encirclements made about the origin of the nyquist plot of the open loop TF:1/[(s-1)(s+2)(s+3)].

 

17. Given a two port network in the form of a T find o/p admittance in terms of y-parameters.

 

18. For a radioactive sample which decays to 12.5% of its initial value in x days, the half life is given by..

 

19. Connect two 1? resistors in series, then connect two 1H inductors across one of the resistors such that the ckt looks like a 1? resistor in series with a ?-section of a resistor and two inductors. With the series resistance on the i/p side, calc the transfer function of this ckt

 

20. AC signal conditioning is used for inductive and capacitive/resistive/piezoelectric transducers/all of the above.


21. For a repeater in a PCM cable identify the correct sequence of actions amongst threshold/equalization/etc.

 

22. Major cause of losses in a fibre optic cable: dispersion/total internal refraction/presence of core and cladding/

 

23. Which layer in the OSI model is concerned with printer buffering,etc: network/session/transport/

 

24. The nyquist sampling rate of the function [sin(at)/t]2 will be

 

25. The feedback topology that results in increased i/p and o/p impedance is current series/voltage series/current shunt voltage shunt.

 

26. Numerical on cardiac output calculation given heart rate and volume per beat.

 

27. Maximum and minimum probability error among ASK,PSK,FSK,DPSK etc

 

28. O/p of a delta modulator when a ramp input is fed to it.

 

29. Steady state error with ramp i/p for a type-0 system.

 

30. Creeping occurs in energy meters bcoz.

 

31. Ultrasonic method of flow measurement cannot be used in liquids with air bubbles/has less attenuation in air compared to liquid-identify the false statement (if any) among these.

 

32. Which of the following is a non linear modulation scheme: PAM/QAM/PCM

 

33. Match the following functions: e-t , e-t + et, sin(?t) with causal and stable system, causal and unstable system, etc.


34. Reset control is another name for integral/derivative/proportional/. Control.

 

35. Time response of system having transfer function 625/(s2+25) will be of the form

 

36. Given some transfer function calc the peak response time.


37. In an ECG instrumentation amplifier the differential gain is provided by 1st stage/2nd stage/mismatched resistors/output stage.

 

38. Classic 3-op amp instrum amplifier.

 

39. Reproducibility of measurements is called accuracy/precision/linearity/none of these.

 

40. Which of these is not strictly a static characteristic accuracy/precision/tolerance/linearity.

 

41. For measuring inductance of high Q coils the bridge used is Maxwell-wien/Schering/

 

42. Which of these measures inductance in terms of capacitance Maxwell and hay/Maxwell and Schering/hay and Schering/

 

43. Given some function F(j?) calc its inverse CTFT.

 

44. Relation between laplace and z-transform: s=z/ s=ln z/ s=( ln z/T) /

 

45. Computer assisted tomography is used for

 

46. Numerical on electrostatic instrument, to calculate deflection given spring constant, torque etc.

 

47. To obtain 10 mV resolution on 5 V range how many bit DAC is to be used..

 

48. Why is LCD preferred to LED.

 

49. How will 0.6973 be displayed on 10 V range of a 4 digit multimeter.

 

50. To prevent loading of a ckt i/p impedance of a CRO should bee high/low/inductive/capacitive.


51. Which is an effective measure of the noise related performance of an amplifier: SNR/noise ratio/thermal noise/shot noise.

 

52. Given baseband signal freq and carrier freq calc which of the freq given will not be present for conventional AM.

 

53. Distinction between FM and PM at high frequencies.

 

54. BIBO stability criterion implies that poles are within/outside/on the unit circle.

 

55. In FM relation between no of sidebands w.r.t. modulating freq

 

56. Numerical on DPSK.

 

57. Superposition can be applied to a ckt with initial conditions/non-linear ckt/

 

58. Kelvins double bridge is used for the measurement of

 

59. Which of these is not an active transducer thermocouple/solar cell/RTD/none of these.

 

60. Oscillator using positive feedback has gain of 0/?/undefined value/

 

61. A multiplexer accepts input data and provides one output all the time/one output at a time/many outputs at a time/many outputs all the time.

 

62. Pulse modulation is essentially a process of multiplexing/.

 

63. For faithful amplification of low amplitude signals the cut-off/active/saturation regions of a transistor is used.

 

64. Lissajous pattern of a signal rotates 36 times per minute. if the oscillator frequency is 560 kHz then the unknown freq is

 

65. Which of these has the least propagation delay RTL/ECL/I2L/CMOS.

 

66.  Switching speed of CMOS is affected/unaffected by changes in supply voltage.

 

67. Addition of a zero to a 2nd order underdamped system results in increase/decrease of rise time and increase/decrease of peak overshoot.

 

68. for PI ctrl we obtain improved bandwidth/improved steady state performance/ worsened steady state performance

 

69. SNR of normal AM system is comparable/3 dB lower/3 dB higher/6 dB lower over DSB-SC and SSB system.

 

70. Which of these provides a measure of heart rate P/QRS complex/T/none of these.

 

71. % resolution of a 10 bit ADC.


72. Which of the following cannot be used for an automatic feedback temp ctrl system thermocouple/thermometer/thermistor/IC sensor.

 

73. y(n)=x(-n+3) is an example of a linear/non linear and shift variant/invariant system.

 

74. The falling body method is used to determine viscosity/humidity/.

 

75. Given a ckt of a logarithmic amplifier you had to identify what ckt was it.

 

76. JFET can operate in depletion/enhancement/both/none of the above modes.

 

77. When a BJT operates in saturation the junctions are fwd biased/reverse biased

 

78. Which of these methods of viscosity measurement gives greatest accuracy falling body method/rotating cylinder method/both/

 

79. A 240 kHz signal is given into a 3 bit binary ripple counter. The lowest o/p freq obtainable is.

 

80. For parity bit checking which of the following gates can be used XOR/NAND/OR/XNOR.

 

81. Some question on gas chromatography

 

82. Find the transfer function from a block diagram.

 

83. In a twisted ring counter the initial count is 1000. after the 4th clock pulse its state will be.

 

84. Why is a BJT called so..

 

85. Identify the expression for gauge factor of a strain gauge among the given options.

 

86. In a semiconductor strain gauge as tensile strain is applied what changes take place in the n and p areas..

 

87. Synchronous ctrs are preferred to asynchronous ctrs bcoz they are faster/glitches at the output can be avoided/both/none of these.

 

88. The lissajous figure formed on an oscilloscope looks like the English figure of 8. if the vertical channel input is 1 kHz the horizontal input freq is.


89. A device having a rotor with 3 Y-connected coils and a stator is likely to be a synchro/RVDT/control transformer/


90. How does a radioactive level gauging system work

 

91. A capacitive transducer measuring level works on the principle of change in distance between plates/change in dielectric strength/

 

92. In a flip-flop with preset and clear inputs both are applied simultaneously/clear is cleared when preset is applied/preset is cleared when clear is applied/.

 

93. What happens when the RET instruction is encountered by 8085

 

94. A 1024*8 memory chip needs how many address lines

 

95. What happens when the PUSH instruction is encountered by 8051.

 

96. IE=IC for a transistor in saturation/cutoff/active/both saturation and active regions.

 

97. Wave shape is altered by clipper/clamper/voltage doubler/amplifier.

 

98. 4 signals of frequencies 100,100,200 and 400 Hz are sampled at nyquist rate and sent through

TDM on a channel.the bandwidth of the channel is..

 

 

Section B. Electrical

 

1. What is given on the name plate of motor? 1) KW 2) KVA 3) output shaft power

 

2. Short circuit test of transformer gives what?

 

3. Transformer core are laminated for what purpose?

 

4. A RC circuit having r=0.8ohm, c=2.5micofarad what will be the time constant?

 

5. Find load impedance if c=0.1 micro farad?

 

6. Two capacitors connected in series the equivalent capacitance is 0.03uf and when connected in parallel the equivalent capacitance is 0.16uf find out the ratio of the two capacitance?

 

7. What is causal system?

 

8. Shunt reactor is used in EHV transmission line for

 

9. In general how transformer is rated?

 

10. What is supply voltage for heavy industry 

 

11. Basic structure SCR as a two transistor i.e. how they are connected?

 

12. What is Triac?

 

13. Synchronous machine can be operated at both lagging and leading power factor

 

14. What does synchronous speed mean?

 

15. Frequency of emf generated per rotation of rotor is equal to.

 

16. DC machine having wave winding is wounded as lap winding what will be the effect

on emf generated

 

17. System admittance is (G+jB) what is reactive power absorbed if the voltage is V KV?

 

18. 20w, 40W, & 200w lamps are connected to three phases if neutral wire breaks then which lamp will fuse first? 1) 20 2)40 3)200 three lamps will fuse together.

 

19. Which is remain unchanged in transformer action?

 

20. In transformer windings are connected.?

 

21. For series R-L-C circuit the load will be capacitive if the frequency is 

 

22. In Wiens bridge which circuit elements determine the frequency range?

 

23. What is the output if two booster having duty cycle K and (K-1) are connected in series?

 

24. If a DC shunt motor is loaded from unloaded condition what will be effect of on terminal voltage?

 

25. In series R-L circuit what is phase difference between the voltage drop across R and L?

 

26. Power factor is cosine (delta ) delta is the angle between

 

1) phase voltage phasecurrent

2)Line voltage lone current

3) phase voltage line current

4) line voltage phase current.

 

27. Laplace of exp (-at)?

 

28. Nature of current and voltage in the armature and at the terminal in DC machine.

 

29. Motor acts on the principle of ..rule

 

30. Which instrument measure both ac and dc?

 

31. A second wire system having one pole one right half of the s-plane. When the system will be stable?

 

32. A system having repetitive pole what will be effect on the gain at the cross over frequency?

 

33. Hollow conductor is used to reduce corona loss how does it reduce the loss?

 

34. In DC machine how voltage is related to flux?

 

35. Z-transform of sampled function x(n) for n>0.

 

36. How the rotation of induction motor is reversed?

 

37. If 3-phaseof a 3- phase balance load are reversed what will be the effect on the line

current?

 

38. If the rating of VAR absorber is 50MVAR at 400KV. What will the VAR absorbed by the absorber at 300KV?

 

39. Laplace transform of impulse function.

 

40. Z-transform of unity.

 

41. In regenerative breaking of DC series motor what is done?

 

42. Definitions of Fourier transform?

 

43. Laplace of f(t) is F(S) what is Laplace of f(t+T) .

 

44. How many slip rings are there in 3phase synchronous motor?

 

45. A synchronous generator having inertia constant 4 and having rating of 100MVA.What will be energy stored by the machine?

 

46. A transformer having ratio 20:1. The secondary load is 0.6 ohm and the voltage across it is 6 V what will be the primary current?

 

47. How the speed of synchronous motor is controlled?

 

48. Speed control of induction motor?

 

49. When power supply is supplied to heater coil it glows while simple wire does not glow. Why?

 

50. Peak to peak value of voltage if rms voltage is 100V.

 

51. Rms voltage.

 

52. What is the approx efficiency of nuclear power plant?

 

53. What is the average current of a single phase full wave rectifier firing at angle alpha?

 

54. What is the function of freewheeling diode?

 

55. Incremental fuel cost of two plants is given and a load is given. Find out the load sharing for economic operation of the plant?

 

56. A two port network is represented by ABCD parameters. What will be condition for the two port network to be symmetrical?

 

57. Size of the conductor is determined by .

 

58. Which Surface is suitable for grounding?

 

59. When SCR stops conduction? (holding current)

 

60. For measuring current why shunt resistance is used?

 

61. For economic operation of plant what is the condition?(taking into account the penalty factor)

 

62. An L-c circuit having frequency 1/sqrt (LC) what will the equivalent impedance?

 

63. An inverting op-am having input with resistance in series and a capacitance in feedback operates as a.?

 

64. A current having fundamental and third harmonics what will be the rms value of the

current?

 

 

Section C. Mechanical

 

1. What will happen if the speed of the centrifugal pump doubles.

 

2. The unit eV is widely used in ? (Nuclear and atomic physics)

 

3. What will happen to the resistance, when the diameter of the conductor is doubled?

 

4. A planet gear with 25 teeth is meshed with a sun gear of 100 teeth. Both are connected using a arm.How many rotations are needed for planet gear to complete one rotation around the sun gear?

 

5. Which is not present in CI engines? (carburrettor)

 

6. Problems in involving with fricition coefficient.

 

7. Factor of safety = Yeild stress/Working stress.

 

8. What is equivalent spring constant for spring in parallel?

 

9. The power comsumed by a electrical device is 1000W at 250V, What is the resistance in the device?

 

10. Some questions was asked related to boundry layer and vortex flow.

 

11. 5 questions were asked in PERT, Process planning, Product planning, Break even analysis.

 

12. How are tungsten and sintered composite materials are machined? (Electro Discharge Machining,

EDM)

 

13. A body weighs 3 kg in air. If it is submerged in a liquid, it weighs 2.5 kg. What is the specific gravity of the liquid.

 

14. A problem in force calculation in a body moving in a inclined surface.

 

15. Composition of bronze. (Copper+zinc)

 

16. Compostion of stainless steel.(iron+chromium+nickel+carbon)

 

17. CI is manifactured in which process. (cupola process)

 

18. What percentage of carbon is preset in pig iron. (4.5 to 6%)

 

19. Two cars travell in same direction at 40 km/hr at a regular distance. A car comes in a opposite

direction in 60km/hr. It meets each car in a gap of 8 seconds. What is the distance between them?

 

20. A simple problem involing in hoops stress. For sphere: M= [3/2]*p*V*[density of pressure vessel

material/Maximum working stress it can tolerate] For Thin walled pressure walls: Hoops stress or

stress in the radial direction =p*r/2t

 

21. Water is available at 10m height. What is the pressure available? (pressure=density*g*height;

p=1000*9.81*10; p=98100N/m2)

 

22. Unit of Entropy (J/kg K or kJ/kg K)

 

23. A mass of 100kg is falling from a height of 1 m and penetrates the sand into for 1 m. What is the

resistance force given by sand.

 

24. Ratio of specific heats of air. (1.41)

 

25. Why DC current is not used in transformer.

 

26. What will happen if one cylinder recieves more amount of fuel spray from injectors than other

injectors?

 

27. Purpose of draft tube in hydraulic turbines? (The purpose of a draft tube is toconvert some of the

kinetic energy of the flow from the runner (the rotating part of the turbine) intopressure energy and thereby increase the efficiency ofthe hydro power turbine. )

 

28. What is the effect or reheater in the gas turbine? (The advantage of reheater is significantly increased thrust; the disadvantage is it has very high fuel consumption and inefficiency).

 

29. On what principle the sonar/ radar( I dont remember) works?

 

30. Bending moment diagram for the UDL is in what shape?

 

31. Function of the distributor in petrol vehicles? (Spark timing)

 

32. Which is the example of non parallel power transmission (Universal coupling)

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