UGC NET Exam December 2014 Electronic Science Paper-3 Question Paper With Answer Key

ELECTRONIC SCIENCE

PAPER – III

Note : This paper contains seventy five (75) objective type questions of two (2) marks each. All questions are compulsory.

1. The basic purpose of biasing a transistor with a network is

(A) to reduce the power dissipation

(B) to improve the gain

(C) to improve the stability

(D) to improve the frequency response

Ans: (C)

2. The depletion capacitance Cj of an abrupt p-n junction diode with uniform doping on either side varies with reverse VR as

Ans: (C)

3. The Laplace transform converts integro-differential equation in _________ domain.

(A) 6

(B) S

(C) jw

(D) ξ

Ans: (B)

4. The switch is thrown to position 1. What will be the current in the circuit in the steady state condition ?

(A) 1A

(B) 2A

(C) 3A

(D) 4A

Ans: (B)

5. Which of the following oscillations makes use of both positive and negative feedback ?

(A) Hartley

(B) Collpitt

(C) Phase shift

(D) Wein Bridge

Ans: (D)

6. The active filter works well

(A) at all frequencies

(B) at high frequencies

(C) at zero frequency

(D) at audio frequencies

Ans: (D)

7. The number of flip-flops required to divide input frequencies by (32)

(A) 3

(B) 4

(C) 5

(D) 6

Ans: (C)

8. Which flip-flop can be used as latch ?

(A) R-S Flip-flop

(B) J-K Flip-flop

(C) T- Flip-flop

(D) D- Flip-flop

Ans: (A)

9. The I/O devices can be accessed in a memory map using the 8085 μp instruction

(A) IN addr or OUT addr

(B) LDA addr or STA addr

(C) MOV M, A or MOV A, M

(D) MVI M data

Ans: (B)

10. Which flag of 8051 works as 1-bit accumulator ?

(A) C

(B) FO

(C) P

(D) OV

Ans: (A)

11. Which bitwise operator is suitable for turning off a particular bit in a number ?

(A) && operator

(B) & operator

(C) | | operator

(D) ! operator

Ans: (B)

12. Which storage class is used for the variables that are often required in a program ?

(A) STATIC

(B) REGISTER

(C) EXTENT

(D) AUTO

Ans: (B)

13. When the Q of an antenna increases, the bandwidth

(A) increases

(B) decreases

(C) remains constant equal to zero

(D) equal to unity

Ans: (B)

14. The information capacity (bits/sec.) of a channel with bandwidth W and transmission time T is given by

(A) WT

(B) W/T

(C) T/W

(D) W2/T

Ans: (D)

15. ________ diode is not used as a microwave mixer or detector.

(A) Schottky diode

(B) PIN

(C) Crystal

(D) Backward

Ans: (B)

16. A super-heterodyne receiver has an intermediate frequency (IF) of 465 kHz. If it is tuned to a station broadcasting at 500 kHz and its oscillator operating at 965 kHz, then image frequency would be

(A) 1530 kHz

(B) 1430 kHz

(C) 1210 kHz

(D) 1020 kHz

Ans: (B)

17. UJT relaxation oscillator is a special case of

(A) Astable multivibrator

(B) Monostable multivibrator

(C) Bistable multivibrator

(D) Astable multivibrator with duration of the semistable state zero

Ans: (D)

18. After firing an SCR, if the gate pulse is removed, the SCR current 

(A) remains the same

(B) reduces to zero

(C) rises up

(D) rises a little and then falls to zero

Ans: (C)

19. In a normal ECG wave form, which wave has the maximum amplitude ?

(A) P-wave

(B) R-wave

(C) Q-wave

(D) T-wave

Ans: (B)

20. If the characteristic equation of a closed loop system is S2 + 2S + 2 = 0, then the system is

(A) over damped

(B) critically damped

(C) underdamped

(D) undamped

Ans: (C)

21. The doping concentration of n-p-n transistor are

i. 5 × 1018 / cm3

ii. 1017 / cm3

iii. 2 × 107 / cm3

Identify the regions in the above order i, ii and iii.

(A) C, B, E

(B) E, B, C

(C) C, E, B

(D) E, C, B

Ans: (D)

22. Which is not a proper way of array declaration ?

(A) int num [6] = {2, 4, 12, 5, 45, 5}

(B) int a(25) ;

(C) int n [ ] = {2, 4, 12, 5, 45, 5}

(D) float press [ ] = {12.3, 34.2, –23.4, –11.3}

Ans: (B)

23. Exponentiation operation in C is carried out as

(A) a = 3 * * 2

(B) a = 3 ^ 2

(C) a = pow (3, 2)

(D) a = 3 exp(2)

Ans: (C)

24. The phase method for generation of a SSB signal is most suitable for

(A) data signals

(B) weak modulating signals

(C) larger bandwidth modulating signals

(D) smaller bandwidth modulating signals

Ans: (D)

25. Which of the following sensors has excellent linearity ?

(A) RTD

(B) Thermo-couple

(C) Radiation Pyrometer

(D) Si based IC chip

Ans: (D)

26. The sinusoidal transfer functions are commonly represented by

(A) Routh’s criteria

(B) Nyquist criteria

(C) Bode Plot

(D) Root Locas

Ans: (C)

27. Which of the following digital modulation systems support high bit rate ?

(A) ASK

(B) PSK

(C) FSK

(D) ASK & FSK

Ans: (B)

28. 

What is the modulus of the counter ?

(A) 1

(B) 3

(C) 2

(D) 4

Ans: (D)

29. Pointer Vector for an electromagnetic wave is

Ans: (C)

30. An amplifier has open-loop voltage gain of 40.10% of negative feedback is effected. What will be the gain with feedback ?

(A) 40

(B) 32

(C) 16

(D) 8

Ans: (D)

31. In a p-n junction diode

1. In reverse bias mode the bulk resistance is dominant.

2. The junction impedance is variable.

(A) Statements 1 and 2 are correct.

(B) Statements 1 and 2 are wrong.

(C) Statement 1 is wrong while statement 2 is correct.

(D) Statement 1 is correct while statement 2 is wrong.

Ans: (C)

32. Read the following statements :

ST 1 : y-parameters can be obtained from Z parameters.

ST 2 : It is not necessary to define y-parameters separately.

(A) ST 1 is correct, ST 2 is wrong.

(B) ST 1 is wrong, ST 2 is correct.

(C) ST 1 and ST 2 are wrong.

(D) ST 1 and ST 2 are correct.

Ans: (A)

33. Negative feedback in amplifier results in

1. reduced voltage gain

2. reduced bandwidth

3. increased S/N ratio

4. reduced distortion of these

(A) 1 and 2 are correct.

(B) 1, 3 and 4 are correct.

(C) 2, 3 and 4 are correct.

(D) 1 and 2 are correct.

Ans: (B)

34. K-map method of simplifications can not be applied when the given functions is in

1. Sum of product forms

2. Product of sum forms

3. Canonical forms

4. Can be applied to all forms

(A) 1 and 2 are correct.

(B) 1, 2 and 4 are correct.

(C) 3 only

(D) 2 & 4 are correct.

Ans: (ALL OPTIONS ARE CORRECT)

35. Read the following statements :

ST 1 : Queue is provided in 8086.

ST 2 : Slow memory does not degrade speed operation of 8086.

(A) ST1 and ST2 are wrong.

(B) ST1 and ST2 are correct.

(C) ST1 is wrong and ST2 is correct.

(D) ST1 is correct and ST2 is wrong.

Ans: (B)

36. Which operators can be used with float ?

1. %

2. *

3. /

4. =

(A) operators 1, 2

(B) operators 1, 2, 3

(C) operators 2, 3, 4

(D) operators 1, 2, 3, 4

Ans: (C)

37. Binary ASK modulation gives

ST1 : High noise immunity

ST2 : Large bandwidth

(A) ST1 is wrong, ST2 is correct.

(B) ST1 is correct, ST2 is wrong.

(C) ST1 and ST2 are wrong.

(D) ST1 and ST2 are correct.

Ans: (A)

38. Which of the following are Maxwell equations ?

Select the correct answer :

(A) 1, 2 and 3

(B) 2, 3 and 4

(C) 3 and 2

(D) 3 and 1

Ans: (A)

39. For SCR which statements are correct ?

ST1 : SCR should be fired with zero gate current.

ST2: failure occurs due to temperature.

(A) ST1 and ST2 are wrong.

(B) ST1 and ST2 are correct.

(C) ST1 is correct and ST2 is wrong.

(D) ST1 is wrong, ST2 is correct

Ans: (A)

40. In comparison to LED, LASER has

1. high emission frequency

2. no tuning arrangement

3. narrow spectral bandwidth

4. provision for confinement of these

(A) 1, 3 and 4 are correct.

(B) 1, 2 and 4 are correct.

(C) 1 and 3 are correct.

(D) 2, 3 and 4 are correct.

Ans: (C)

41. Which of the following are useful in comparing the noise performance of receivers ?

1. Input noise voltage

2. Equivalent noise resistance

3. Noise temperature

4. Noise figure

Select the correct answer.

(A) 1, 2 and 4

(B) 1, 3 and 4

(C) 2, 3 and 4

(D) 1, 2 and 3

Ans: (C)

42. Which is not the effect of addition of open loop zeroes on the stability of the system ?

1. increasing stability

2. making system oscillatory

3. decreasing stability

4. shifting root-locas towards imaginary axis

(A) 1, 2, 3

(B) 1, 3, 4

(C) 2, 3, 4

(D) 1, 2, 4

Ans: (C)

43. Consider the following :

1. In semiconductors, the mobility of electrons is more than that of holes.

2. In semiconductors, the resistivity increases with the increase in temperature.

3. Metal has positive TCR.

4. In metals, thermal conductivity is inversely proportional to electronic conductivity at a particular temperature.

Which of the following statements are correct ?

(A) 1, 2, 3

(B) 1, 2, 4

(C) 2, 3, 4

(D) 1, 3, 4

Ans: (D)

44. Which of the following circuits will have transients ?

1. Resistive

2. R-L

3. R-C

4. R-L-C

Which is correct ?

(A) 1, 2

(B) 2, 3

(C) 3, 4

(D) 2, 3, 4

Ans: (D)

45. Consider the following :

ST1 : F.M. signal produces more side bands than A.M.

ST2 : The carrier in a F.M. signal can never be dropped to zero amplitude.

Which of the following is valid ?

(A) Neither ST1 nor ST2

(B) Both ST1 and ST2

(C) ST1 and not ST2

(D) ST2 and not ST1

Ans: (B)

46. 8085 μp instructions are given below

1. STA addr

2. CALL addr

3. MOV Rd, Rs

4. ADI data

Arrange these in the ascending order of number of clock cycles required to execute them.

(A) 1, 2, 3, 4

(B) 3, 4, 1, 2

(C) 2, 4, 3, 1

(D) 4, 3, 2, 1

Ans: (B)

47. If P → Passivation, Q →  n-well implant, R → Metallization and S → Source/ drain diffusion

The sequence in which these are carried out in a n-channel CMOS fabrication is

(A) P – Q – R – S

(B) Q – S – R – P

(C) R – P – S – Q

(D) S – R – Q – P

Ans: (B)

48. Arrange the following NINV – Op-Amps in the increasing order of the bandwidth :

1. unity gain

2. gain = 10

3. gain = 100

4. gain = 20

(A) 1, 2, 3, 4

(B) 2, 3, 4, 1

(C) 1, 2, 4, 3

(D) 3, 2, 1, 4

Ans: (C)

49. Arrange the following devices in the increasing order of 8-bit general purpose registers these contain :

1. 8085

2. 8051

3. 8086

4. 8255

(A) 4, 1, 3, 2

(B) 1, 4, 3, 2

(C) 3, 2, 4, 1

(D) 2, 3, 1, 4

Ans: (A)

50. Arrange in the increasing order of temperature coefficient :

1. Zener diode with breakdown voltage 6 V

2. Zener diode with breakdown voltage > 6V in series with a p-n diode

3. Zener diode with breakdown voltage < 6 V

4. Zener diode with breakdown voltage < 6 V in series with a Si-Pn junction diode

(A) 3, 2, 4, 1

(B) 4, 1, 3, 2

(C) 2, 3, 1, 4

(D) 1, 4, 2, 3

Ans: (B)

51. Match the given lists :

Ans: (A)

52. Match the given lists :

Ans: (B)

53. Match the following :

Ans: (D)

54. Match the following :

Ans: (B)

55. Match the following :

Ans: (B)

56. Match the following :

Ans: (C)

57. Match the following :

Ans: (A)

58. Match the following :

Ans: (C)

59. Match the following :

Ans: (A)

60. Match the following :

Ans: (B)

Directions for questions 61 to 70 : The following items consists of two statements, one labelled the “Assertion (A)” and the other labelled “Reason (R)”. You are to examine the two statements carefully and decide if the Assertion (A) and Reason (R) are individually true and if so, whether the reason is a correct explanation of the Assertion. Select your answer to these items using the codes given below and mark your answer accordingly.

Codes :

(A) Both (A) and (R) are true and (R) is the correct explanation of (A).

(B) Both (A) and (R) are true, 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 avalanche breakdown, the temperature coefficient is positive.

Reason (R) : In zener breakdown the temperature coefficient is positive.

Ans: (C)

62. Assertion (A) : Capacitor input filter gives a high output voltage which drops as the load is increased.

Reason (R) : Capacitor input filters produce more heating in the rectifiers.

Ans: (B)

63. Assertion (A) : Op-Amp is used for sensor circuit.

Reason (R) : A small signal amplifier amplify weak measured signals.

Ans: (A)

64. Assertion (A) : Dual slope (A/D) converter is the most preferred conversion technique employed in most of the digital multimeters.

Reason (R) : Dual slope (A/D) converter provides high accuracy while at the same time suppresses the HUM effect on the input signal.

Ans: (A)

65. Assertion (A) : Any program written for 8080 will run without any changes on 8085.

Reason (R) : Any program written for 8086 will run without changes on 8085.

66. Assertion (A) : ‘C’ provides a switch statement.

Reason (R) : In order to select one alternative out of many, there is no provision in C. It has to be done by user defined function.

Ans: (C)

67. Assertion (A) : The system of propagation in waveguide is in accordance with field theory.

Reason (R) : The system of propagation in transmission lines is in accordance with circuit theory.

Ans: (B)

68. Assertion (A) : Amplitude modulation is wastage of power.

Reason (R) : Amplitude modulation is wastage of bandwidth.

Ans: (A)

69. Assertion (A) : A number of thyristors operating in parallel cannot share a common heatsink.

Reason (R) : For simultaneous firing of the thyristor opto-isolator may be employed in the gate driving circuit.

Ans: (D)

70. Assertion (A) : The shift in the position of the bright spot on the CRO screen per unit change of voltage across the deflection plates is called deflection sensitivity.

Reason (R) : The path traveled by the spot on a CRO screen during the retrace time is called retrace path.

Ans: (B)

Read the passage and answer the questions 71 to 75 that follow based on your understanding of passage :

General methods of n/w analysis become laborious and time consuming for large and complex network. For such situations the solution is network theorems. Besides, the other features of n/w theorems are

(A) they are applicable to a useful and fairly wide class of networks.

(B) their conclusions are simple and

(C) they sometimes provide good physical insight into the problems.

The maximum power transfer implies that the load impedance must be the complex conjugate of the source impedance. The superposition theorem is valid for any linear, time invariant or time varying. It is useful in circuit analysis when the n/w has large number of sources. Thevenin’s or Norton’s theorem is applicable to any number of time invariant or time varying n/w. It is useful when only one part of the n/w is varying, while the other part remains constant. Thevenin’s equivalent ckt is the voltage source equivalent at the terminals concerned. Millman’s theorem is
the extension of Thevenin’s or Norton’s theorem for a number of Current or Voltage sources respectively. The substitution theorem is applicable to any network and can be applied to a branch which is not coupled to other branches of the network. Telleng’s theorem is applicable to any lumped n/w regardless of the type of elements, which may be linear or non-linear, time varying or time invariant.

71. The principle of superposition is the property of

(A) additivity only

(B) homogeneity only

(C) combined property of additivity and homogeneity of linear n/w s

(D) additivity and associativity

Ans: (C)

72. Which equivalent circuits are dual ?

(A) Norton-Telleng

(B) Thevenin-Superposition

(C) Norton-Thevenin

(D) Thevenin-Millman

Ans: (C)

73. In Thevenin equivalent circuit which is incorrect :

(A) Independent voltage sources are open circuited.

(B) Independent voltage sources are short circuited.

(C) Dependent voltage sources are removed.

(D) Current sources are opened.

Ans: (A)

74. For the n/w, find RTH

(A) 2 Ω

(B) 3 Ω

(C) 4 Ω

(D) 6 Ω

Ans: (B)

75. Find out which of the following statements is wrong ?

The principle of superposition is useful for

(A) linearity test of a system

(B) substituting sources by their shunt impedances.

(C) superposition applies to V-I relationship also

(D) In superposition theorem, response of each source is considered separately.

Ans: (B)