DMRC Junior Engineer (Electronics) Solved Question Paper

Delhi Metro Rail Corporation Examination

Junior Engineer (Electronics) Solved Question Papers

1. Which one of the following statements is correct?
Digital modulation techniques are used in satellite communication systems since:

1. They are easier to handle
2. Large bandwidth utilization is possible
3. They have a higher spectral efficiency
4. They are less prone to interference

2. How many bits are required to encode 32 level PCM:

1. 6
2. 5
3. 4
4. 3

3. The noise is more dominant in which of the following:

1. (1) PAM
2. PWM
3. PPM
4. FSK

4. The phase velocity of wave propagating in a hollow metal wave guide is:

1. (1) Greater than the velocity of the light in free space
2. Less than the velocity of the light in free space
3. Equal to the velocity of the light in free space
4. Equal to the group velocity

5. The magnitude of the open-circuit and short circuit input impedance of a transmission line are 100 ohm and 25 ohm respectively. The characteristic impedance of line is:

1. 25 ohm
2. 50 ohm
3. 75 ohm
4. 100 ohm

6. The line of sight communication requires transmit and receive antenna to face each other. If the transmit antenna is vertically polarized, for the best reception the receive antenna should be:

1. Horizontally polarized
2. Vertically polarized
3. At 45° with respect to the horizontal polarization
4. At 45° with respect to the vertical polarization

7. A network contains linear resistance and ideal voltage source. If the value of all the resistors are doubled, then the voltage across each resistor is:

1. Halved
2. Doubled
3. Increased by four times
4. Not changed

8.Twelve 1 ohm resistances are used as edge to form a cube. The resistance between two diagonally opposite corners of the cube is:

1. 5/6 ohm
2. 1 ohm
3. 6/5 ohm
4. 3/2 ohm

9. An eight bit digital data 10101100 is fed to an ADC. The reference voltage is +10V. The analog output voltage will be:

1. 1.05V
2. 6.74V
3. 10.10V
4. 5.15V

10. A series RLC circuit has a resonant frequency of 1 KHz and a quality factor Q = 100. If each of the R,L and C is doubled from its original value, the new Q of the circuit is:

1. 25
2. 50
3. 100
4. 200

11. The input to a coherent detector is DSB-SC signal plus noise. The noise at the detector output is:

1. The in-phase component
2. The quadrature-component
3. Zero
4. The envelope

12. Gunn diode is a:

1. Negative resistance device
2. Positive resistance device
3. High noise device
4. Low frequency device

13. The intrinsic carrier concentration of silicon sample at 300° K is 2.5×1016/m3. If after doping, the number of majority carriers is 5×1020 /m3, the minority carrier density is:

1. 1.25×1012/m3
2. 0.125×1012/m3
3. 2.5×1020/m3
4. 0.5×104/m3

14. The unit of ?× H is:

1. Ampere
2. Ampere/meter
3. Ampere/meter2
4. Ampere-meter

15. A PIN diode is:

1. A metal semiconductor point-contact diode
2. A microwave mixer diode
3. Often used as a microwave detector
4. Suitable for use as a microwave switch

16. 11001, 1001 and 111001 correspond to the 2’s complement representation of which one of the following sets of number?

1. 25, 9 and 57 respectively
2. –6, –6 and –6 respectively
3. –7, –7 and –7 respectively
4. –25, –9 and –57 respectively

17. To couple a coaxial line to a parallel wire line, it is best to use a:

1. A slotted line
2. Balun
3. Directional coupler
4. Quarter wave line transformer

18. Which of the following is used extensively where lowest power consumption is necessary?

1. CMOS
2. NMOS
3. PMOS
4. Any of the above

19. Reflex klystron is a:

1. Low power generator
2. High power oscillator
3. Low gain amplifier
4. Not an oscillator

20. If the radiated power of AM transmitter is 10 KW, the power in the carrier for modulation index of 0.6 is nearly:

1. 8.24 KW
2. 9.26 KW
3. 8.47 KW
4. 9.6 KW

21. The current through 8 ohms branch is:

1. 1A
2. 0.5A
3. 1.5A
4. None of these

22. JFET in properly biased condition acts as a:

1. Current controlled current source
2. Voltage controlled voltage source
3. Voltage controlled current source
4. Impedance controlled current source

23. The circuit shown in figure is best described as a:

1. Bridge rectifier
2. Ring modulator
3. Frequency discriminatory
4. (4) Voltage doubler

24. Which amplifier will be preferred for highest gain?

1. Darlington pair
2. Cascade amplifier
3. Cascode amplifier
4. Depends on the circuitry

26. Without any additional circuitry, an 8:1 MUX can be used to obtain:

1. Some but not all Boolean functions of 3 variables
2. All function of 3 variables but none of 4 variables
3. All functions of 3 variables and some but not all of 4 variables
4. All functions of 4 variables

27. The resolution of a potentiometer should be:

1. Zero
2. Low
3. High
4. Infinite

28. Negative feedback in amplifier:

1. Improves the SNR at input
2. Improve SNR at output
3. (3) Reduces distortion
4. Decreases bandwidth

29. Spectral density expresses:

1. Average voltage
2. Average current
3. Average power in a waveform as a function of frequency
4. None of these

30. Which of the following is used as a data selector?

1. Encoder
2. Decoder
3. Multiplexer
4. De-multiplexer

31. If a signal x(n)=x(–n), then it is called ____ signal:

1. Odd
2. Energy
3. Power
4. Even

32. The response of an LTI/LSI system is given by the _______ of input and impulse response:

1. Convolution
2. Correlation
3. Superposition
4. None

33. Companders are used in communication systems to:

1. Compress bandwidth
2. To improve frequency response
3. To improve signal to noise ratio
4. None of these

34. ICB0 in a transistor can be reduced by reducing:

1. IB
2. VCC
3. IE
4. Temperature

34. Light is confined within the core of a simple optical fiber by:

1. Refraction.
2. Total internal reflection at the outer edge of the cladding.
3. Total internal reflection at the core cladding boundary.
4. Reflection from the fiber's plastic coating.

36. The complement of AB+BC’+CD’ is:

1. A’CD+B’C’+B’D
2. A’C’+BC+AB’D’
3. AC+BC+ABD
4. A’C’+B’C’+A’B’D’

37. The following expression when simplified will become XY(X’YZ +X’Y’Z’+XY’Z)

1. 0
2. 1
3. –1
4. X

38. In a PCM system of telemetry, the quantization noise depends on:

1. The sampling rate and quantization level
2. The sampling rate only
3. The number of quantization level
4. Information provided is not sufficient

39. In PCM system, if we increase the quantization levels from 2 to 8, the relative bandwidth requirements will:

1. Be doubled
2. Remain same
3. Be tripled
4. Becomes eight times

40. The modulation system inherently most noise resistant is:

1. Frequency modulation
2. Pulse width modulation
3. (3) Pulse code modulation
4. Phase modulation

41. Which of the following microphone does not require polarizing current?

1. Crystal microphone
2. Condenser microphone
3. Carbon microphone
4. All of the above

42. The large signal bandwidth of an opamp is limited by its:

1. Loop gain
2. Slew rate
3. Output impedance
4. Input frequency

43. In an unclocked R-S flip flop made of NOR gates, the forbidden input condition is:

1. R=0, S=0
2. R=1, S=0
3. R=0, S=1
4. (4) R=1, S=1

44. A phase-locked loop (PLL) is a feedback circuit consisting of a:

1. Phase detector.
2. Low-pass filter.
3. VCO.
4. All of these

45. A 339 IC is an example of a fourteen-pin DIP that can be made to function as a ________:

1. Comparator
2. 555 timer
3. D to A converter
4. Ladder network

46. Filters with the ___ characteristic are useful when a rapid roll-off is required because it provides a roll-off rate greater than –20/dB/decade/pole:

1. Butterworth
2. Chebyshev
3. Bessel
4. Elliptical

47. Which of the following applications include a phase-locked loop (PLL) circuit?

1. Modems
2. AM decoders
3. Tracking filters
4. All of these

48. Rectification efficiency of a fullwave rectifier without filter is nearly equals to:

1. 51%
2. 61%
3. 71%
4. 81%

49. What is the voltage resolution of an 8-stage ladder network?

1. Vref /128
2. Vref /256
3. Vref /512
4. Vref /1024

50. In which region is the operating point stable in tunnel diodes?

1. Negative-resistance
2. Positive-resistance
3. Both negative- and positive-resistance
4. Neither negative- nor positive-resistance

51. Which of the following diodes is limited to the reverse-bias region in its region of operation?

1. Schottky
2. Tunnel
3. Photodiode
4. Rectifier

52. Which of the following semiconductor materials is (are) used for manufacturing solar cells?

1. Gallium arsenide
2. Indium arsenide
3. Cadmium sulfide
4. All of these

53. If Y (s) - {(S 2 - 1)/8}, the network has:

1. 1 H inductor and 1 F capacitor in parallel
2. 1 H inductor and 1 F capacitor in series
3. 1 H inductor and 1 O resistor in series
4. 1 H inductor and 1 O resistor in parallel

54. When the temperature of a doped semiconductor is increased, its conductivity

1. Decreases
2. Increases
3. Does not change
4. Increases or decreases depending on whether it is p-type or n-type

55. Schering bridge is used to measure

1. Frequency
2. Inductance
3. Capacitance
4. Mutual Inductance

56. A step voltage E is applied to a series R-L circuit. The rate of change of current is maximum at t = _:

1. Zero
2. Infinity
3. L/R
4. R/L

57. PLAs, CPLDs, and FPGAs are all which type of device?

1. SLD
2. (2) PLD
3. EPROM
4. SRAM

58. Holding current for an SCR is best described as:

1. The minimum current required for turn-off
2. The current required before an SCR will turn on
3. The amount of current required to maintain conduction
4. The gate current required to maintain conduction

59. What type of temperature coefficient do thermistors have?

1. Positive
2. Negative
3. (3) Either positive or negative
4. None of these

60. In a microprocessor:

1. One machine cycle is equal to one clock cycle
2. One clock cycle consists of several machine cycles
3. One machine cycle consists of several clock cycles
4. One machine cycle is always less than one clock cycle

61. In 8085 microprocessor with memory mapped I/O which of the following is true?

1. I/O devices have 16 bit addresses
2. I/O devices are accessed during IN and OUT instructions
3. There can be a maximum of 256 input and 256 output devices
4. Logic operations can not be performed

62. A blank EPROM has:

1. All bits set to logical 0
2. All bits set to logical 1
3. Half the total number of bits set to 0 and remaining half to logical 1
4. Either 0 or 1

63. One application of a digital multiplexer is to facilitate:

1. Code conversion
2. Parity checking
3. Parallel-to-serial data conversion
4. Data generation

64. The coefficient of coupling between two coils is 0.45. The first coil has an inductance of 75 mH and the second coil has an inductance of 105 mH. What is the mutual inductance between the coils?

1. 3.54 mH
2. 7.88 mH
3. 39.9 mH
4. 189.3 mH

65. The fast carry or look-ahead carry circuits found in most 4-bit parallel-adder circuits:

1. Increase ripple delay
2. Add a 1 to complemented inputs
3. Reduce propagation delay
4. Determine sign and magnitude

66. To multiply a number by 8 in 8085 we have to use RAL instruction:

1. Once
2. Twice
3. Thrice
4. Four times

67. An energy signal has G(f) = 10. Its energy density spectrum is:

1. 10
2. 100
3. 50
4. 20

68. Feedback factor at the frequency of oscillation of a Wien bridge oscillator is:

1. 3
2. 1/3
3. 1/29
4. 3/29

69. A 4-bit R/2R digital-to-analog (DAC) converter has a reference of 5 volts. What is the analog output for the input code 1010:

1. 0.3125 V
2. 3.125 V
3. 0.78125 V
4. –3.125 V

70. A quarter wave line open circuited at far end behaves as:

1. Inductance
2. L and C in parallel
3. Capacitance
4. L and C in series

71. In a directional coupler:

1. Isolation (dB) equals coupling plus directivity
2. Coupling (dB) equals isolation plus directivity
3. Directivity (dB) equals isolation plus coupling
4. Isolation (dB) equals (coupling) (directivity)

72. In a circular waveguide the dominant mode is:

1. TE01
2. TE11
3. TE20
4. TE21

73. In a klystron amplifier the input cavity is called:

1. Buncher
2. Catcher
3. Pierce gun
4. Collector

74. A loss less line of characteristic impedance Z0 is terminated in pure reactance of –jZ0 value. VSWR is

1. 10
2. 2
3. 1
4. Infinity

75. The velocity factor of a transmission line depends on:

1. Temperature
2. Skin effect
3. Relative permittivity of dielectric
4. None of these