### 2013 December UGC NET Examination in Electronic Science, Paper III: Previous Years Solved Question Paper Along With Answer Keys

1. In an npn transistor, the expression for avalanche multiplication factor is given by
(A) M = 1/((1 + VCB/B VCBO)n
(B) M = (1 + VCB/B VCBO)n
(C) M = (1 – VCB/B VCBO)n
(D) M = 1 / [1 – (VCB/B VCBO)n]
Where, VCB is collector to base voltage and BVCBO is maximum reverse biasing voltage which may be applied before breakdown between the collector and base terminals.

2. In a bipolar transistor, stability factor for a fixed bias circuit is given by
(A) S = 1/ (1 + β)
(B) S = 1/ (β – 1)
(C) S = (β – 1)2
(D) S = β + 1

3. In a Wein bridge oscillator circuit, the value of frequency can be calculated by the following expression:
(A) fo = 1 / 2π RC
(B) fo = 1 / 2π LC
(C) fo = 1 / 2π L1(C1 + C2)
(D) fo = 1 2π (R21 + R22) (C21+ C22)

5. A square coil has the dimensions 0.2 m × 0.2 m and carrying a current of 3.0 A in a field of 10 wb/m2. The value of Torque is given by
(A) 10.2 N – m
(B) 1.02 N – m
(C) 0.12 N – m
(D) 1.2 N – m

6. For a transmission line which isterminated in a normalised impedance Zn, VSWR = 2, the value of normalised impedance is given by
(A) 2
(B) 1/2
(C) 3
(D) 1/3

9. Which of the following circuit comes under the class of sequential logic circuits?
(A) Multiplexer
(B) RS Latch
(D) ROM

10. The Hamming code for 0110 using even parity is
(A) 0010110
(B) 1010110
(C) 1100110
(D) 1110110

11. Phase Lock Loop (PLL) system is used for the detection of
(A) PM
(B) AM
(C) FM
(D) QAM

12. A transistor amplifier has a measured S/N of 10 at its input and 5 at its output. The transistor’s Noise Figure (NF) in dB is
(A) 2 dB
(B) 3 dB
(C) 6 dB
(D) 10 dB

13. A signal varies from 20 Hz to 5 KHz is passed using pulse modulation scheme. Minimum sampling rate and number of channels that could be accommodated using TDM (assume each sample takes 10 μs) respectively will bewww.netugc.in
(A) 5 KHz, 5
(B) 10 KHz, 5
(C) 5 KHz, 10
(D) 10 KHz, 10

14. The term (1/jw) on the log-magnitude plot has a slope of

15. The Routh Array is as below:
S6         1          8          20        6
S5         2          12        16
S4         2          12        16
S3         0          0
The row of zero of this ray will be replaced by coefficients of:
(A) S4 + 12 S2 + 16
(B) S3 + 3 S
(C) S4 + 6 S2 + 8
(D) S3 + 12 S

16. Zener breakdown mechanism occurs in reverse biased PN junction
(A) When P and N regions are lightly doped.
(B) When P and N regions are heavily doped.
(C) Are of silicon material only.
(D) When P and N regions are equally doped.

17. The operation of a Photo-diode involves
(A) Photo-conductive effect
(B) Photo-voltaic effect
(C) Photo-emissive effect
(D) Photo-multiplicative effect

18. A UJT has RBB = 10 K and RB2 = 4 K. Its intrinsic stand-off ratio is
(A) 0.6
(B) 0.4
(C) 2.4
(D) 3.5

19. The triggered voltage of a SCR is close to
(A) 0.3 V
(B) 0.7 V
(C) 3 V
(D) Breakdown voltage

20. A thyristor can be used as
(A) An amplifier
(B) A resistor
(C) A switch
(D) A power source

21. Which of the following is an advantage to use fiber optic data transmission?
(A) Resistance to the data theft
(B) Fast data transmission rate
(C) Low noise level
(D) All of the above

22. A breakdown which is caused by cumulative multiplication of carriers through field induced impact ionization occurs in
(A) Avalanche diode
(B) Tunnel diode
(C) Varactor diode
(D) Gunn diode

23. Transfer function of a system is necessary for the calculation of
(A) The time constant
(B) The output for a given input
(D) The order of the system

24. If one or more pairs of simple roots are located on imaginary axis of the s-plane but there are no roots in the right half of s-plane, the response due to initial condition will
(A) Decrease to zero as time approaches infinity.
(B) Increase as time approaches infinity.
(C) Be undamped sinusoidal oscillations.
(D) Be damped unsinusoidal oscillation and the damping factor will depend upon the relative location of the roots on the imaginary axis.

25. 8255A Programmable Peripheral Interface IC has got the 24 I/O lines in the following way (General form):
(A) Port A with 8 input lines, Port B with 8 output lines, Port C (upper nibble) with 4 input lines and Port C (lower nibble) with 4 output lines.
(B) Port A with 8 input/out lines, Port B with 8 input lines and Port C with 8 output lines.
(C) Port A with 8 input lines, Port B with 8 output lines and Port C with 8 bits as either input or output lines.
(D) Port A with 8 lines as input/output lines, Port B with 8 lines as input/output lines, Port C (lower nibble) with 4 lines as input/output lines. Port C (upper nibble) with 4 lines as input/output lines.

26. C program is as follows: The result of the program is
int i; /*…declare integer i…*/
i=10; /*…set i to 10 …*/
/*…to integer i…*/
print f (“i=%d”, i);
(A) 55
(B) 51
(C) 71
(D) 75

27. Consider the following conditional expression z = (x > y)? x: y; if x = 2 and y = 8, the value of z is
(A) 2
(B) 8
(C) 6
(D) 10

28. int Net = 0;
if x < 50
if (y > 5)
Net = x + y;
else
Net = x – y;
For this C program segment, x = 55 and y = 5, then the value Net is
(A) 0
(B) 60
(C) 50
(D) 55

29. In 8253 programmable interval timer, in which modes, the counting is neither enabled nor disabled?
(A) 0 and 4
(B) 1 and 5
(C) 1 and 4
(D) 3 and 5

30. In which mode of 8259A programmable interrupt controller, all the Interrupt Requests (IRs) are arranged from highest to lowest with IR0 as the highest and IR1 as the lowest?
(A) Fully Nested Mode
(B) Automatic Rotation Mode
(C) Specific Rotation Mode
(D) Simple Rotation Mode

32. In an OPAMP, following characteristics are given:
1. PSRR (Power Supply Rejection Ratio) = 0
2. Thermal Drift is defined in terms of μ Amperes/°C.
3. Thermal drift is defined in terms of μV/°C.
4. Slew rate is defined in terms of V/μs.
Which one of the following is correct?
(A) 1 and 2 only
(B) 1 and 3 only
(C) 1, 3 and 4
(D) 1, 2 and 4

33. Consider the following statement:
(i) A flip-flop is used to store 1-bit of information.
(ii) Race-around condition occurs in J-K flip-flop when both the inputs are 1.
(iii) Master-slave configuration is used in flip-flop to store 2-bits of information.
(iv) A transparent latch consists of D type flip-flop.
Which of the following statements is/are true?
(A) (i) only
(B) (i), (iii) and (iv)
(C) (i), (ii) and (iv)
(D) (ii) and (iii) only

34. An AM demodulator can be implemented with
(i) A linear multiplier followed by a low pass filter.
(ii) A linear multiplier followed by a high-pass filter.
(iii) A diode followed by low pass filter.
(iv) A linear multiplier followed byband-stop filter.
(A) (i) only
(B) (iii) only
(C) (i) and (iii)
(D) (iv) only

35. In feedback control system, relative stability can be calculated usingwww.netugc.in
(i) Routh-Hurwitz Array
(ii) Nyquist plot
(iii) Polar plot
(iv) Root Locus Techniques
(A) All of the above
(B) (i) and (ii) only
(C) (ii) and (iv) only
(D) (ii), (iii) and (iv)

36. In comparison to LED, LASER has
1. High emission frequency.
2. No tuning arrangement.
3. Wide spectral bandwidth.
4. Provision for confinement.
Of these statements:
(A) 1, 2 & 4 are correct.
(B) 1, 2, & 3 are correct.
(C) 1 & 4 are correct.
(D) 2 & 3 are correct.

37. The turn-off time of an SCR can be reduced by
1. Quick withdrawal of the gate voltage.
2. Reducing life-time by doping with gold.
3. Applying a negative voltage pulse to the gate.
Of these statements:
(A) 1, 2 and 3 are correct.
(B) 1 and 2 are correct.
(C) 1 and 3 are correct.
(D) 2 and 3 are correct.

38. Consider the following statements regarding a semiconductor:
1. Acceptor level lies close to the valence band.
2. Donor level lies close to the valence band.
3. n-type semiconductor behavesas a conductor at zero Kelvin.
4. p-type semiconductor behaves as an insulator at zero Kelvin.
Of these statements:
(A) 2 and 3 are correct.
(B) 1 and 3 are correct.
(C) 1 and 4 are correct.
(D) 3 and 4 are correct

39. Transfer function for a control system is defined for where
(i) Linear system
(ii) Nonlinear system
(iii) Time invariant system
(iv) Time variant system
(A) (i) and (iii)
(B) (ii) and (iv)
(C) (i) and (iv)
(D) (ii) and (iii)

40. Tri state Buffers provide
(i) Reduction of current consumption in the circuit.
(ii) Isolation from input to output.
(iii) High impedance during OFF state.
(iv) Low impedance during ON state.
(A) (i) and (iv)
(B) (ii) and (iv)
(C) (i) and (ii)
(D) (i) and (iii)

41. Consider the following:
1. CE stage
2. CC stage
3. OP amp
4. CB stage
The correct sequence of the input impedance in increasing order is:
(A) 4, 1, 2, 3
(B) 1, 4, 2, 3
(C) 1, 2, 4, 3
(D) 4, 2, 1, 3

42. The various components in super heterodyne receiver is arranged as
(i) AM Detector
(ii) Mixer
(iii) RF Amplifier
(iv) AF Amplifier
The correct sequence is
(A) (iii), (ii), (i), (iv)
(B) (i), (ii), (iv), (iii)
(C) (iii), (ii), (iv), (i)
(D) (ii), (i), (iii), (iv)

43. Fora unity feedback control system having an open-loop transfer function
G(S) = [K(S + 2)] / S2(S4 + 7 S + 12)
The error constant Kp, Kv and Ka respectively are
(A) ∞, ∞, K/6
(B) 0, 0 , K/6
(C) ∞, 0 , K/6
(D) 0, ∞, K/6

44. Arrange in ascending order the following logic families based on power delay products
(i) ECL
(ii) TTL
(iii) CMOS
Codes:
(A) (ii), (iii), (i)
(B) (ii), (i), (iii)
(C) (i), (ii), (iii)
(D) (iii), (ii), (i)

45. Consider the following four common type of transistors:
1. Point Contact Transistor
2. Bipolar Junction Transistor
3. MOS Field Effect Transistor
4. Junction Field Effect Transistor
Correct arrangement of these transistors in the increasing order of input impedance is
(A) 1, 2, 4, 3
(B) 1, 2, 3, 4
(C) 2, 1, 3, 4
(D) 2, 1, 4, 3

46. If the various logic families are arranged in the ascending order of their fan-out capabilities, the sequence will be
(A) TTL, DTL, ECL, MOS
(B) DTL, TTL, MOS, ECL
(C) MOS, DTL, TTL, ECL
(D) ECL, TTL, DTL, MOS

47. Consider the following waves/rays:
1. UV Rays
2. X Rays
3. Visible light
4. UHF waves
The correct sequence of the descending order in terms of frequency is:
(A) 3, 1, 2, 4
(B) 4, 3, 1, 2
(C) 2, 1, 3, 4
(D) 2, 4, 1, 3

48. The structure of a decision table, divided into four parts like
 1 4 2 3
(i) Condition Stub
(ii) Condition Entries
(iii) Action Stub
(iv) Action Entries
(A) (i), (ii), (iv) and (iii)
(B) (ii), (iv), (iii) and (i)
(C) (i), (iii), (iv) and (ii)
(D) (i), (iv), (ii) and (iii)

49. The parameters associated with time response of control system are
(i) Delay time (td)
(ii) Settling time (ts)
(iii) Rise time (tr)
(iv) Peak time (tp)
Arrange the above in the order, the parameter which is having minimum time to the parameter which has got the maximum time.
(A) (i), (iv), (ii) and (iii)
(B) (i), (iii), (ii) and (iv)
(C) (i), (iv), (iii) and (ii)
(D) (i), (iii), (iv) and (ii)

50. In the Assembly program, the following steps are to be followed. Find the sequence in which the program to be written for 8085 microprocessor.
(i) Initialization of variables.
(ii) Initialization of stack.
(iii) Enable or disable interrupts.
(iv) Program should be completedwith last line as ‘END’statement.
(A) (i), (iii), (ii) and (iv)
(B) (i), (ii), (iii) and (iv)
(C) (ii), (i), (iii) and (iv)
(D) (ii), (iii), (i) and (iv)

51. Match the following lists:
List – I                                                                        List - II
(a) Alpha of Transistor                                                (i) > 1
(b) Beta of Transistor                                                  (ii) ∞
(c) CMRR (Common Mode Rejection Ratio)            (iii) < 1
(d) PSRR (Power Supply Rejection Ratio)                (iv) 0
The correct match is:
(a)        (b)        (c)        (d)
(A)       (iii)       (i)         (ii)        (iv)
(B)       (iv)       (i)         (ii)        (iii)
(C)       (i)         (ii)        (iii)       (iv)
(D)       (ii)        (i)         (iii)       (iv)

52. Match the following lists:
List – I                        List - II
(a) Magnetron                         (i) Detector
(b) Pin diode               (ii) Bunching
(c) Klystron                 (iii) Low Power Oscillator
(d) Gunn diode           (iv) π-mode
The correct match is:
(a)        (b)        (c)        (d)
(A)       (ii)        (iii)       (iv)       (i)
(B)       (i)         (ii)        (iii)       (iv)
(C)       (iii)       (i)         (ii)        (iv)
(D)       (iv)       (i)         (ii)        (iii)

53. Match the following lists:
List – I                                    List - II
(a) Companding                      (i) Improving image rejection
(b) Squelch                              (ii) Variation of step rise in quantisation
(c) Preemphasis                       (iii) Muting the receiver
(d) Double conversion            (iv) Boosting of higher modulating frequencies at the transmitter
Codes:
(a)        (b)        (c)        (d)
(A)       (ii)        (iii)       (iv)       (i)
(B)       (ii)        (i)         (iv)       (iii)
(C)       (i)         (ii)        (iii)       (iv)
(D)       (i)         (ii)        (iv)       (iii)

54. Match the following lists:
List – I            List - II
(a) 74150         (i) Quad 2: 1 Multiplexer
(b) 74152         (ii) Dual 4: 1 Multiplexer
(c) 74153         (iii) 8: 1 Multiplexer
(d) 74157        (iv) 16: 1 Multiplexer
Codes:
(a)        (b)        (c)        (d)
(A)       (i)         (ii)        (iii)       (iv)
(B)       (iv)       (iii)       (ii)        (i)
(C)       (iv)       (ii)        (iii)       (i)
(D)       (ii)        (i)         (iv)       (iii)

55. Match the following lists:
List – I                                                List - II
(Characteristic of the device)              (Device)
(a) Voltage controlled device                         (i) BJT
(b) Current controlled device              (ii) UJT
(c) Conductivity modulated device    (iii) FET
(d) Negative conductance device       (iv) IMPATT
Codes:
(a)        (b)        (c)        (d)
(A)       (ii)        (iii)       (i)         (iv)
(B)       (ii)        (iii)       (iv)       (i)
(C)       (iii)       (i)         (iv)       (ii)
(D)       (iii)       (i)         (ii)        (iv)

56. Match the following lists:
List – I                                                            List - II
(a) Optical fiber communication         (i) FDM
(b) Mobile communication                  (ii) TDM
(c) Digital communication                  (iii) CDMA
(d) Analog communication                 (iv) Wavelength- Division Multiplexing (WDM)
Codes:
(a)        (b)        (c)        (d)
(A)       (i)         (iii)       (ii)        (iv)
(B)       (iv)       (iii)       (ii)        (i)
(C)       (ii)        (iv)       (i)         (iii)
(D)       (iii)       (i)         (ii)        (iii)

57. (a) Bode’s-Plot representation      (i) not a frequencydomaintechnique.
(b) Nyquist Diagram                           (ii) low frequency and high frequency characteristics of the transfer function can be determined
(c) Nichols Charts                               (iii) decides the Stability criteria
(d) Root-locus Method                       (iv) also known as Polar plots
(a)        (b)        (c)        (d)
(A)       (iv)       (iii)       (i)         (ii)
(B)       (iv)       (iii)       (ii)        (i)
(C)       (iii)       (iv)       (i)         (ii)
(D)       (ii)        (iii)       (iv)       (i)

58. The following are features of a micro controller 8051:
(i) 4 k bytes of ROM or EPROM
(ii) 128 k bytes of data memory
(iii) Four programmable I/O ports
(iv) Three 16 bit timer/event counters.
(A) (i), (ii) and (iii)
(B) (i), (ii) and (iv)
(C) (i), (iii) and (iv)
(D) (ii), (iii) and (iv)

59. Identify the peripheral devices for their applications.
(a) 8155           (i) Serial Communication
(b) 8279           (ii) Timers and Counters
(c) 8253           (iii) Keyboard and display interface
(d) 8251          (iv) Additional input/output lines to processor
Codes:
(a)        (b)        (c)        (d)
(A)       (ii)        (iii)       (iv)       (i)
(B)       (iii)       (iv)       (i)         (ii)
(C)       (iv)       (i)         (ii)        (iii)
(D)       (iv)       (iii)       (ii)        (i)

60. Match the following lists:
List – I                                                List – II
a Stability of Control System                         1. Oscillation in which the amplitude decreases with time.
bUnstability of Control System          2. All roots of characteristic equation have negative real part.
c Frequency response                          3. Steady state response
d Damped Oscillation                         4. Any root of characteristic equation has a positive real part
Codes:
a          b          c          d
(A)       4          2          3          1
(B)       2          4          3          1
(C)       2          4          1          3
(D)       4          2          1          3

Directions: Q. Nos. 61 to 70, the following items consist of two statements, one labelled the “Assertion (A)” and the other labelled the “Reason (R)”. You are to examine these two statements carefully and decide if the Assertion (A) and the Reason (R) are individually true and if so, whether the Reason (R) is a correct explanation of the Assertion (A). Select your answers to these items using the codes given below and mark your answer accordingly.
Codes:
(A) Both (A) and (R) are correct and (R) is correct explanation of (A).
(B) Both (A) and (R) are correct, but (R) is not correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

61. Assertion (A): In amplifiers, it is easy to compare two powers on a Logarithmic rather than on linear scale. It is called decibel.
Reason (R): Decibel is defined as N = 10 log P2 / P1 , where P2 is output power and P1 is input power.

62. Assertion (A): Magnetron is not cross field devices.
Reason (R): They make use of electric and magnetic fields simultaneously. The fields are perpendicular to each other.

63. Assertion (A): TDM can be employed to transmit channels having unequal bandwidths.
Reason (R): If sampling theorem is strictly followed, any analog signal can be reconstructed back from the samples.

64. Assertion (A): A NAND gate is called a Universal logic element.
Reason (R): Any logic function can be realized using NAND gates alone.

65. Assertion (A): The stability of a control system can be determined from the location of roots of characteristic equation.
Reason (R): For stability the roots should lie on the left half of s-plane.

66. Assertion (A): The intrinsic Fermi level of a semiconductor does not lie exactly at the middle of the energy band gap.
Reason (R): The densities of the available states in valence and conduction bands of an intrinsic semiconductor areequal.

67. Assertion (A): The operating principle of Laser is based on stimulated emission process.
Reason (R): In coherent radiation, the emitted photons have same phase, same polarization and same direction with the incident photon.

68. Assertion (A): A microprocessor interfaced with inputs, outputs and other peripheral devices is also called a micro controller system and is capable of controlling the process.
Reason (R): The microprocessor is a device which processes the instructions.

69. Assertion (A): In control system design, the transfer function consists of both poles and zeros. To make the system stable, the poles plotted in Bode plot should be near to origin.
Reason (R): The zeros must be also near to origin.

70. Assertion (A): A p-channel enhancement MOSFET based transistor can be turn on prematurely.
Reason (R): Most contaminants in MOS fabrication are mobile positively charged ions and they get trapped between the gate and the substrate in an n-channel enhancement MOSFET, whereas they are trapped on the other side of the substrate in the case of a p-channel enhancement MOSFET.

The field effect transistor is a semiconductor device which depends for its operation on the control of current by an electric field. There are two types of field effect transistor, the Junction Field Effect Transistor (JFET) and Metal-Oxide- Semiconductor (MOSFET) FETs operation depends upon the flow of majority carriers only. It is therefore a unipolar device. BJT is a bipolar device. FET is relatively immune to radiation and it exhibits a high input resistance tipically many mega-ohms. It is less noisy than a tube or a bipolar transistor. It exhibits no offset voltage at zero drain current, and hence makes an excellent signal chopper. FETs are more temperature stable than BJTs. JFET is three terminal devices with gate applied potential control the flow of charges from source to drain. The n-channel MOSFET consists of a lightly p-type substrate into which two highly doped n+ regions are diffused. These n+ sections, which will act as the source and drain. A thin layer of insulating SiO2 is grown over the surface of the structure and holes are cut into the oxide layer, allowing contact with the source and drain. This layer results in an extremely high input resistance.

71. The point above the drain voltage, where there is no increase in drain current in a JFET is called as
(A) Break down point
(B) Pinch off point
(C) Knee point
(D) Critical point

72. FET is disadvantageous in comparison with BJT because of
(A) High input impedance
(B) Low noise
(C) High gain bandwidth behaviour
(D) Current controlled behaviour

73. For an n-channel silicon FET with α = 3 × 10–4 cms and ND = 1015 electron/cm3, find the pinch is of voltage. [= 120 1/4π0 = 9 × 109 (Newton – m2) /Coulomb]
(A) 6.00 V
(B) 5.4 V
(C) 6.8 V
(D) 4.5 V

74. An FET is a better chopper than BJT because it has
(A) Higher series on resistance
(B) Lower input current
(C) Higher input impedance
(D) Lower off-set voltage