**NTPC Previous years solved question papers**

**No of Questions : 170**

**Technical -120**

**Aptitude-50 **

**Time limit : 2 Hours
In Aptitude section Refer RS aggarwal book is enough
Technical Section : Good in basics, Time management important factor
The questions were from following topics-**

10-12 Questions about microprocessor(8085)

3 Questions about RS232 standard

7-10 Questions of GK

4-6 Questions on opamp

10-15 Questions on Digital Communications

2-5 Questions on microwaves

15-20 Questions on Analog Devices

20-23 Questions on Digital Electronics (flip flops,gates,mux,no system etc)

1 Questions on ISO OSI Model

5-8 Questions on Control System

10-12 Questions on Signals and their Processing

1. Passage

2. Word meaning based (antonym and synonyms) fetter, fester, lucid, anomaly, elucidate etc

3. Word analogy based quqestions

4. What is a tunnel diode

5. What is a Zener diode

6. Effect of + and – feedback on stability

7. Composition of gobar gas

8. Function of differential in the vehicle

9. Function of stack register

10. Fun of instruction pointer

11. Fun of rst6.5,7.5

12. Wht is an interrupt

13. Output vtg calc on op amp

14. How a pulse train can b generated using registers

15. Conversion of oct to hex,hex to binary

16. Fun of quantizer in pcm

17. Why fm is less prone to noise

18. Fun of limiter in detection of FM

19. What is envelop detector

20. Phase shift of 1/s^2

21. Signal limited to 1000 hz sampled at nyquist rate. quantizer has 128 level .calculate the bit rate of the system.

22. 1.5 V battery supply same power to R1 and R2 separately(R1>R2).calc the internal resistance of battery

23. A wire is cut in two halves. one half is again stretched to the twice of length .calc the resistance.

* An ice block submerged in the water, if the ice melts level of water (increase, decrease, remains same, none)

* Simply supported beam with w point load at the middle, max. bending moment? (wl/4)

* Simply supported beam with UDL ,max.deflection (wl4/384EI)

* Cantilevel beam point load at tip,max.bending momemt comes at (end)

* When bearing life L10 represents (bearings 10%survive,bearings 10% fails, none )

* For welding high carbon steels which type of flame is used (oxidizing, carburizing, neutral, none)

* Arrange the following cutting tools in decreasing order of machining hardness…Ceramics

* When P1 and P2 are the loads acting on bearings with life L1 and L2 then L1/L2=? L1/L2={P2/P1}10/3

* Product simplification does not mean? (Product characterization)

* Which of the following process has the most scope in manufacturing? CAD/CAM, CAM, CIM, All the above.

* Concurrent engineering means? (Manufacturing, designing, both, none)

* Which manufacturing process yields higher output and increases worker productivity- (process layout, line+process, functional layout)

* 18-4-1 represents-, Tungsten-Cr-Vn

* For which material is negative allowance rovided-(Graphite,steel,bronze,cast iron)

* What is the recrystallisation temperature of tin- (60,300,1000,none)

* What is the purpose of borax in soldering-

* Top gates are provided in which type of casting-(Shallow casting,simple,complex,none)

* Which statement is true regarding simple gear trains-(i/p and o/p shafts r fixed, each shaft has 2 gears, i/p & o/p shafts r moving)

* What is the purpose of normalizing- (Refining of grain structure)

* As the grain size is decreased-(Hardness increases,corrosion resistance decreases,both)

* Isothermal gas is filled in a vessel at a pressure P and temperature T then considering the compressible forces as the height increases pressure ??(linearly increases linearly decreases exponentially increase )

* A bottle is filled with water and air and is tied to a string and is rotated in horizontal direction. Then in which direction will air bubble travel?

(bottom,neck,uniformly spread)

* A empty bottle(in vaccum) filled with a gas at temp T and press P when the pressure of bottle reaches P temperature of the gas is _? (T,T/K,TK)

* Bearing somerfield number _ with load on bearing? (increases,decreases,no change)

* Critical radius for a sphere is-(2k/h)

* Critical radius exist for_ (spherical,cylindrical,both,slab)

* Convectional resistance/internal resistance is called (biot number)

* Nusselt no. is? (hl/k)

* EOQ=?

* Which statement is true regarding critical path method? (i only one critical path exists for a network, more than one with same duration,)

* Shipment cost,inspection cost,storage cost comes under_ (carrying cost ,holding cost,)

* Ischronous governers sensitivity is- (zero,infinite)

* Self energized brakes are-(friction moment acts in the direction of application of force,opposite to the direction of force, does not need a force to act ,)

* The ratio of heat capacities for evaporator and condenser is_ (Zero,infinity)

* When steam and air mixture with partial pressure 0.06 and 0.07 enters a condenser what is the condenser pressure? (0.06,0.07,0.53,0.03)

* In pulverized burning of coal heat transfer from boiler to water occurs through_( predominant radiation, convection, conduction, conduction+convection)

* Rankine cycle efficiency for same parameters increases mostly with_(reheat, regeneration, super heating )

* Ericson cycle with all reversible processes assume_(carnot cycle,stirling,brayton

* Air delivery tank at outlet of reciprocating compressor is provided for_ (provide constant pressure, avoid cavitation, )

* High speed centrifugal pump has _? (vanes faces in forward direction side,backward,radial vanes)

* Thermal efficiency in decreasing order_? (Otto cycle>dual cycle>diesel cycle)

* When a 1000 K body comes in contact with atmosphere at 300K a loss of 9000 KJ heat is transferred. The net available energy transferred is_

* When entropy of a system increases_? (unavailable energy increases )

* Rolling is a process widely used for_?

* Tool nomenclature_?

* In francis turbine movement of steam?

* For low power consumption _? (rake angle should be increased / decreased, nose angle increased/ decreased)

* Continuous chips occur in_? (High speeds,low speeds,both,none)

* Primary forces in a reciprocating engine_? (fully balanced, partially balanced, completely unbalanced, none)

* In proximate analysis pyrogallol is used for analysis of which element_? (nitrogen,oxygen)

* Sulphur content in fuel greatly affects_? (corrosion)

* Heat transfer through radiation can be increased by_? (decreasing emissivity and increases temperature of hot body)

* Which theory of failure clearly explains the failure in case of ductile material? (Maximun shear stress theory or Guests or trescas theory)

When a material is subjected to continuous cycles which limit is being verified? (Endurance limit)

Where is stress concentration maximum? (notches, stress reducing through cuts)

* Power transmitted through a belt drive_? P(T2-T1)

* According to Eulers theory crippling or buckling load is ____ (Wcr = Cπ2EI/l2)

* During sensible heating, specific humidity_? (remains constant)

* COP of a refrigerator is _? (greater than 1 )

* The maximum temperature in a refrigeration cycle is_? (less than/greater than/equal to critical temperature)

* The pressure at the throat of the nozzle_? (maximum,min)

* For a statically determinate set of forces for equilibrium_? (∑ f(X), f(Y), f(Z)=0,∑M=0)

* For a statically determinate set of forces- (there r as many equations as the no. of unknowns)

* 1-2-3 analysis is used for_? (1.break even analysis, ??)

* A problem on mean time of service something like a salesman has a rating of 120. considering 10% allowance time calculate the time required to serve 120?

* A problem n determining time in a queue?

* Energy equation for a laminar flow is _? (Uniform and steady ,non uniform and unsteady)

* Undercuts in welding occurs due to_? (low welding current, high welding current)

* Work holding equipment in shearing?

* At the centre of a nozzle _? (Mach no<1 >=1;=1)

Technical Paper :

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

2. A 4 kHz signal is sampled at thrice the Nyquist rate and sent through a channel with error ≤1%. Calc the bandwidth of the channel.

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

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

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

6. Lower useful input limit of a transducer is determined by…

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

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

9. Expression for δ(n): u(n)-u(n-1)/ u(n-1)-u(n+1)/ u(n)+u(n+1)/...

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

11. Z-transform of 3n u(n).

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

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

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

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

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

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

18. O/P of a delta modulator when a ramp input is fed to it.

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

20. Creeping occurs in energy meters bcoz….

21. 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.

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. Given some function F(jω) calc its inverse CTFT.

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

26. Maxm and minm probability error among ASK,PSK,FSK,DPSK etc

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

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

29. Given a ckt with a 50 Ω resistor in series between two voltage sources of 10 V and 5 V magnitude calc power delivered by 5 V source.

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

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

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

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

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

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

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

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

41. Repeat ques 40 above for the classic 3-op amp instrum amplifier.

42. EMG signals are of the order of mV/V/μV/…

43. Computer assisted tomography is used for…

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

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

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

47. For PI ctrl we obtain improved bandwidth/improved steady state performance/ worsened steady state performance/…

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

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

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

51. Distinction between FM and PM at high frequencies.

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

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

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

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

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

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

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

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

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

61. % resolution of a 10 bit ADC.

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

63. Why is LCD preferred to LED.

64. How will 0.6973 be displayed on 10 V range of a 4 ½ digit multimeter.

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

66. Y(n)=X(-n+3) is an example of a linear/non linear and shift variant/invariant system.

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

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

69. Some question on gas chromatography

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

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

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

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

74. Why is a BJT called so..

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

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

77. How does a radioactive level gauging system work…

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

79. For maximum power transfer in an AC circuit the condition to be satisfied is ZL+ZS=0/XL+XS=0/none of these/….where l and s refers to load and source respectively.

80. Find the transfer function from a block diagram.

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

82. 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….

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

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

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

86. The shunt coil in a Q meter has resistance of the order of mΩ/Ω/kΩ/..

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

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

89. 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/….

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

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

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

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

94. Numerical on DPSK.

95. 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.

96. Pulse modulation is essentially a process of multiplexing/….

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…

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

100. Kelvin’s double bridge is used for the measurement of…

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

102. Oscillator using positive feedback has gain of 0/∞/undefined value/…

103. Wien bridge oscillator should initially have closed loop gain >3/<3/=3/…

104. Some question on gain margin and phase shift of a system.

105. Fourier series expansion of even function has sine terms only/cosine terms only/no odd harmonics/…

106. Full wave rectifier gives clean dc o/p/dc o/p with small ripple/positive half and inverted negative half of i/p as o/p.

107. Which of these values of ζ gives damped oscillations: 0/1/1.6/0.6

108. For a transformer of ratio 1:a and excited by a source V with impedances Z1 and Z2 on the primary and secondary side value of a for maxm power transfer should be..

109. Fourier transform of cos(ω0t) is…

110. At t=0 the step response of a 1st order system is….

111. 555 can be used as a monostable/astable/freq dividing ckt/all of these.

112. In a PT when the secondary is open ckted with the primary excited what will happen.

113. If a system is marginally stable then the nature of oscillations will be…

114. Linear encoders mostly use straight binary/BCD/gray code.

115. For an accelerometer working in displacement mode the ratio of forcing freq to natural freq should be…..

Most of the Aptitude questions we get straightforward. This Paper contains questions involving profit and loss, ratio-proportion, DI from pie-charts, one RC passage and other questions from verbal. Here we have to concern the Verbal questions, which will be quite confusing, as none of the options seemed to fit the question.