NTPC Exam Pattern consists of total 170 Questions.
Out of 170, 150 Questions are Technical and 20 Questions are Non Technical.
This set contains only 48 questions with answers and remaining will posted later.
1. The transfer function of a simple RC network functioning as a controller is:
Ge(s) = s+ Z1/s+ p1
The condition for the RC network to act as a phase lead controller is:
(a) p1 < z1 (b) p1 = 0
(c) p1 = z1 (d) p1 > z1
Ans: (d)
2. The incoming solar radiation at a place on the surface of the earth is 1.2 KW/m^2.
The amplitude of the electric field corresponding to this incident power is nearly
equal to:
(a) 80 mV/m
(c) 30 V/m
(b) 2.5 V/m
(d) 950 V/m
Ans: (d)
3. A 4 bit modulo-16 ripple counter uses JK flip-flop. If the progression delay of each
FF is 50 ms, maximum clock frequency that can be used is equal to:
(a) 20 MH z (b) 10 MHz
(e) 5 MHz (d) 4 MHz
Ans: (c)
4. Two two-port networhs are connected in cascade. The combination is to be represented
as a single two-port networh. The parameters of the network are obtained by multiplying the individual.
(a) z- parameter matrix
(c) y-parameter matrix
(b) h- parameter matrix
(d) ABCD parameter matrix
Ans: (d)
5. White noise is that signal whose frequency spectrum
(a) extends over infinite range (b) has flat spectral density
(c) has spectral density varying as l/f (d) has limited number of frequency components
Ans: (b)
.
6. When electromagnetic waves are reflected at an angle from a wall their wavelength
along the wall is
(a) the same as in free space
(b) the same as the wavelength perpendicular to the wall
(e) shortened because the Doppler effect
(d) greater than in the actual direction of propagation.
Ans: (d)
7. Frequencies in UHF range propagate by means of
(a) ground waves (b) sky waves
(c) space waves (d) surface waves
Ans: (c)
8. The characteristic impedance of a lossless transmission line is given by
(a) Sqrt(LC) (b) Sqrt(L/C)
(c) 1/Sqrt (LC) (d) Sqrt(C/L)
Ans: (b)
9. An air filled rectangular waveguide has dimensions 6 cm, 4 cm. The cut off frequency for TE10 is
(a) 2.5 GHz (b) 25 GHz
(c) 25 MHz (d) 5 GHz
Ans: (a)
10 The maximum usable frequency of an ionospheric layer at 60° incidence with 8 MHz critical frequency is
(a) 16MHz (b) 16/Sqrt (3) MHz
(c) 8 MHz (d) about 6.93 MHz
Ans: (b)
11. The co-axial cables belongs to
(a) TEM class of transmission line (b) quasi-TEM class of transmission lines
(c) non-TEM class of transmission lines (d) none of these
Ans: (a)
12_ The characteristic impedance of a transmission line is
(a) directly proportional to its length (b) inversely proportional to its length
(c) Independent of its length (d) none of these
Ans: (c)
13. Standing wave ration (SWR) on a transmission line
(a) is directly proportional to the load impedance and inversely proportional to characteristic impedance
(b) is directly proportional to the characteristic impedance and inversely proportion to the load impedance
(c) may be defined as either (ZL/Zo) or (Zo/ZL)
(d) none of these
Ans: (c)
14. Two transmission linear have SWRs of (1/6) and 2 respectively
(a) The one with SWR = 2 is better matched to the load
(b) The one with SWR = 1/6 is better matched to the load
(c) Both are equally well matched
(d) none of these
Ans: (a)
15. Standing wave ratio (SWR) equal to unity implies that
(a) the transmission line is open circuited
(b) the transmission line is short circuited
(c) the transmission line's characteristic impedance equals load impedance
(d) none of these
Ans: (c)
16. Higher value of SWR signifies
(a) higher ohmic losses
(b) higher ohmic losses and possibility of insulation breakdown
(c) higher radiation resistance
(d) none of these
Ans: (b)
17. In a synchro error detector, the output voltage is proportional to [w(t)]n where
w(t) is the rotor velocity and n equals
(a) - 2 (b) - 1
(c) 1 (d) 2
Ans: (c)
18. The circuit of Fig. is an example of feedback of the following type
(a) current series
(b) curent shunt
(c) voltage series
(d) voltage shunt
Ans: (d)
19. In a differential amplifier, CMRR can be improved by using an increased
(a) emitter resistance (b) collector resistances
(c) power upply voltages (d) source resistances
Ans: (a)
20. From a measurement of the rise time of the output pulse of an amplifier whose
input is a small amplitude square wave, one can estimate the following parameter
of the amplifier:
(a) gain·bandwidth product
(c) upper 3·dB frequency
(b) slew rate
(d) lower 3·dB frequency
Ans: (c)
21. A PAM signal can be detected by using
(a) an ADC (b) an integrator
(c) a band pass filter (d) a high pass filter
Ans: (b)
22. The signal to quantization noise ratio in an n-bit PCM system
(a) depends upon the sampling frequency employed
(b) is independent of the value of 'n'
(c) increases with increasing value of 'n'
(d) decreases with the increasing value of 'n'
Ans: (c)
23. How many loud speakers are required in a quadraphonic?
(a) Two (b) Three
(c) Four (d) Six
Ans: (c)
24. In a modulation system, on doubling the modulation frequency, the modulation
index gets halved while the modulating voltage needed remains unaltered. The
modulation system is
(a) AM (b) FM
(c) PM (d) All the above
Ans: (b)
25. A cascade amplifier stage is equivalent to
(a) a common emitter stage followed by a common base stage
(b) a common base stage followed by an emitter follower
(c) an emitter follower stage followed by a common base stage
(d) a common base stage followed by a common emitter stage.
Ans: (a)
26. A signed integer has been stored in a byte using the 2's complement format. We
wish to store the same integer in a 16 bit word. We should
(a) copy the original byte to the less significant byte of the word and fill the more
significant with zeros
(b) copy the original byte to the more significant byte of the word and fill the less
significant byte with zeros
(e) copy the original byte to the less significant byte of the word and make each bit of
the more significant byte equal to the most significant bit of the original byte
(d) copy the original byte to the less significant byte as well as the more significant byte
of the word
Ans: (c)
27. A half wave rectifier uses a diode with a forward resistance Rf. The voltage is
Vm sin wt and the load resistance is RL• The DC current is given by
(a) Vm/Sqrt(2RL) (b) Vm/Pai * (Rr + RL)
(e) 2Vm/Sqrt(Pai) (d) Vm/RL
Ans: (b)
28. To prevent loading in the last I.F. amplifier in a receiver, we should use
(a) Squelch circuit (b) variable selectivity
(e) variable sensitivity (d) double conversion
Ans: (c)
29. The spectral density of a real valued random process has
(a) an even symmetry (b) an odd symmetry
(e) a conjugate symmetry (d) no symmetry
Ans: (a)
30. The probability density function of the envelope of narrow band Gaussian noise
is
(a) Poission
(e) Rayleigh
(b) Gaussion
(d) Rieian
Ans: (a)
31. Flat top sampling of low pass signals
(a) gives rise to aperture effect (b) implies over sampling
(e) leads to aliasing (d) introduces delay distortion
Ans: (a)
32. A loop is rotating about the y-axis in a magnetic field B =Bo cos (cot + pai) ax T.
The voltage in the loop is
(a) zero (b) due to rotation only
(e) due to transformer action only (d) due to both rotation and transformer action
Ans: (d)
33. The maxwell equation
(a) Ampere's law
(e) Foraday's law
(b) Gauss low
(d) Coulomb's law
Ans: (a)
34. The polarization of a wave with propagation electric field vector E =Eo[ax+ay] is
(a) linear (b) elliptical
(c) left hand circula,' (d) right hand circular
Ans: (a)
35. The vector H is the far field of an antenna satisfy.
(a) V.H =0 and VxH =0 (c) V.H=O andVxH,.O (d) V.H,.O and VxH =0
Ans: (c)
36. If carrier modulated by a digital bit stream had one of the possible phases of 0,
90, 180, and 270 degrees, then the modulation is called
(0) BPSK (b) OPSK
(c) QAM (Ii) MSK
Ans: (b)
37. The mica layer (e = 7) in a parallel plate capacitor with on effective area of r
120 mm2 has a damaged section equivalent to a hole of 0.5 mm diameter. Which
of the following would be significantly affected by the damage?
(a) capacitance (b) charge
(c) dielectric breakdown strength (d) tan 0
Ans: (c)
38. In a piezoelectric crystal oscillator, the oscillation or tuning frequency is linearly
proportional to the
(a) mass of the crystal
(b) square root of the mass of the crystal
(c) square of the mass of the crystal
(d) inverse of the square root of the mass of the crystal
Ans: (d)
39. The operating state that distinguishes a silicon controlled rectifier (SCR) from a
diode is
(a) forward conduction state (b) forward blocking state
(c) reverse conduction state (d) reverse blocking state
Ans: (b)
40. The number of comparators needed in a parallel conversion type 8-bit A to D
converter is
(a) 8 (b) 16
(c) 255 (d) 256
Ans: (c)
41. An integrating digital voltmeter measure
(a) true average value (b) rms value
(c) peak value (Ii) peak to peak value
Ans: (c)
42. The impulse response of on R-L circuits is a
(a) rising exponential function (b) decaying exponential function
(c) step function (Ii) parabolic function
Ans: (a)
45. An effect of phase-lag compensation on servo system performance is that
(a) for a given relative stability, the velocity constant is increased
(b) for a given relative stability, the velocity constant is decreased
(c) the bandwidth of the system is increased
(d) the time response is made faster.
Ans: (a)
48. The time taken for a surge to travel a 600 km long overhead transmission line is
(a) 6 s (b) 1 s
(c) 0.02 s (d) 0.002 s
Ans: (d)
