ELECTRONICS AND COMMUNICATION ENGINEERING IMPORTANT MCQ-ELECTROMAGNETIC FIELD THEORY

1. When a wave is incident from the more dense into a less dense medium at
an angle equal to or exceeding the critical angle, the wave suffers total
internal __________ .
A. reflection
B. refraction
C. transmission
D. none of the above
Answer: B
2. Radiation intensity in a given direction is the
A. energy radiated per square metre
B. power radiated per square metre
C. power radiated per unit solid angle in that direction
D. none of the above
Answer: C
3. Parabolic and lens antenna used at
A. microwave frequency
B. medium frequency
C. low frequency
D. high frequency
Answer: A
4. Which of the following statement regarding waveguides is incorrect?
A. At waveguide can be coupled to a coaxial cable
B. At frequencies below the cut off value the wave progresses across the
waveguide after total reflections
C. Waveguides are usually air filled hollow conducting metallic tubes for
transmitting UHF and microwaves
D. Waveguides can handle large power at UHF and microwaves
Answer: A
5. The potential that appears at a point in space due to the current which
caused it is called potential
A. accelerating
B. retardation
C. oscillating
D. lagging the current
Answer: B
6. The useful magnetic flux obtainable from any closed surface is
A. unity
B. constant
C. both (a) and (b)
D. none of the above
Answer: D
7. It is best to use for coupling a coaxial line to a parallel wire
transmission line.
A. directional Coupler
B. balun
C. slotted line
D. tee
Answer: B
8. In H-plane metal plate lens the travelling wave front is
A. totally retarded
B. retarded
C. accelerated
D. neither accelerated nor retarded
Answer: B
9. MUF is depend upon
A. electron density of the ionospheric layer
B. 11 year sun spot cycle
C. received frequency by receiver
D. height of ionospheric layer
Answer: C
10. In case of antenna the ratio of the power radiated in the desired
direction to the power radiated in the opposite direction is known as
A. transmission efficiency
B. front to back ratio
C. loss coefficient
D. none of the above
Answer: B
11. The radiation pattern of Hertzian dipole in the plane perpendicular to
dipole is a
A. null
B. circle
C. figure of eight
D. none of the above
Answer: C
12. The transmitting antennas for lower frequencies (below 500 kHz) are
generally
A. vertical grounded wire type
B. horizontal suspended wire type
C. parabolic reflector type
D. any of the above
Answer: A
13. A satellite that simply reflect back the signals from one region of the
earth to the other region is known as
A. orbiting satellite
B. geostationary satellite
C. active satellite
D. passive satellite
Answer: D
14. The critical frequency of ‘F’ layer is greater than 30 MHz.
A. True
B. False
Answer: B
15. Which of the following will increase the antenna radiation efficiency?
A. Use of larger section of conductor
B. Providing insulation on conductor
C. Top loading of antenna
D. Any of the above
Answer: C
16. A waveguide operated below cut off frequency can be used as
A. phase shifter
B. an attenuator
C. an isolator
D. none
Answer: B
17. Which of the following impedance inversion is obtained?
A. Short-circuited stub
B. A quarter wave line
C. Balun transformer
D. A half wave line
Answer: B
18. In case of surface waves the field strength at a point is directly
proportional to
A. antenna height
B. wave frequency
C. current of the antenna
D. distance of the point from the antenna
Answer: D
19. Which of the following statement is false?
A. Television signals are propagated as ground waves
B. Surface waves can propagate on piezoelectric substrates
C. The skip distance is the maximum distance upto which ionospheric reflection
is possible
D. Tropospheric scatter propagation is always subjects to fading
Answer: C
20. Tropospheric scatter is used with frequencies in the
A. HF
B. VHF
C. UHF
D. VLF
Answer: C
21. A Yagi antenna has a driven antenna
A. only
B. with a reflector
C. with one or more directors
D. with a reflector and one or more directors
Answer: D
22. The minimum height of outer atmosphere is
A. 100 km
B. 150 km
C. 200 km
D. 400 km
Answer: D
23. A square corner reflector is used in
A. radio astronomy
B. tv broadcast
C. point to point communication
D. all of the above
Answer: D
24. The wave in wave guide has
A. group velocity inversely proportional to wavelength
B. larger frequency than in the free space
C. diminishing wavelength than in the free space
D. larger wavelength than in the free space
Answer: D
25. The power gain of a half-wave dipole with respect to an isotropic
radiator is
A. 2.15 db
B. 3 db
C. 4.15 db
D. 6 db
Answer: A
26. In an impedance smith chart, a clockwise movement along a constant
resistance circle gives rise to
A. decrease in the value of reactance
B. an increase in the value of reactance
C. no change in the reactance value
D. no change in the impedance value
Answer: B
27. When the phase velocity of an EM wave depends on frequency in any medium
the phenomenon is called
A. scattering
B. polarisation
C. absorption
D. dispersion
Answer: B
28. The main disadvantage of the two-hole directional coupler is
A. poor directivity
B. narrow bandwidth
C. high standing wave ratio
D. low directional coupling
Answer: B
29. The radiation pattern of a parabola antenna is
A. omnidirectional
B. a figure of directional
C. highly directional
D. none of the above
Answer: C
30. In microwave communication links, when fading due to rain attenuation
occurs then technique adopted for solving the problem would include
A. antenna replacement and feed correction
B. amplitude timing and phase correction
C. polarization shifting and code diversity
D. path diversity and frequency diversity
Answer: D
31. Due to which of the following reasons a lightning conductor on top of a
building is made into a pointed spike?
A. Dust particles may not accumulate
B. Charge per unit area becomes very high for lightening to discharge
C. Rain drops may not collect
D. None of the above
Answer: B
32. The virtual height of an ionospheric layer is __________ true height
A. equal to
B. less than
C. higher than
D. no relation
Answer: C
33. The divergence of a vector is a scalar, while the curl of a vector is
another
A. scalar
B. vector
C. unit vector
D. none of the above
Answer: B
34. An open wire transmission line having a characteristic impedance of 600
ohms is terminated by a resistive load of 900 O. The standing wave ratio will
be
A. 1.5
B. 2.5
C. 3.5
D. 4.5
Answer: A
35. The skip distance is the maximum distance upto which ionospheric
reflection is possible.
A. True
B. False
Answer: B
36. Which antenna is a wideband antenna?
A. Hertz antenna
B. Marconi antenna
C. Folded dipole
D. None of the above
Answer: C
37. The radiation pattern of loop antenna is
A. circle
B. semicircle
C. elliptical
D. cardoid or Limacon
Answer: D
38. Tropospheric scatter propagation is not subject to any fading.
A. True
B. False
Answer: B
39. The attenuation in waveguide above to cut off frequency
A. very high
B. very low
C. zero
D. infinite
Answer: B
40. When a current carrying conductor is brought into magnetic field, the
force that moves the conductor depends upon
A. the value of current
B. the weight of the conductor
C. the direction of the conductor
D. none of the above
Answer: A
41. A square corner reflector is used in which of the following?
A. TV broadcast
B. Point-to-point communication
C. Radio astronomy
D. All of the above
Answer: D
42. According to maximum power transfer theorem, the maximum power is
absorbed by one network from another network when
A. the impedance of one of the networks is half that of the other
B. the impedance of one is the complex conjugate of the other
C. the impedance of one is equal to that of the other
D. none of the above
Answer: B
43. The static electric field in a conductor is
A. zero
B. unity
C. infinity
D. none of the above
Answer: A
44. In a perfect conductor the incident and reflected wave combine to
produce
A. a stronger incident wave
B. a stronger reflected wave
C. a standing wave which is not progressing
D. none of the above
Answer: C
45. MUF is highest in periods of greatest sunspot activity.
A. True
B. False
Answer: A
46. Which of the following is multiband HF receiving antenna?
A. Square loop
B. Log-periodic
C. Conical horn
D. Folded dipole
Answer: B
47. A rectangular waveguide is a
A. rectangular conducting wire to propagate electromagnetic waves
B. hollow rectangular walled room carrying electromagnetic wave
C. hollow rectangular conducting tube through which electromagnetic waves can
be propagated
D. tube antenna to transmit and receive electromagnetic waves
Answer: C
48. If a and b are the dimensions of waveguide then
A. a = 3b
B. a = 2b
C. a = b
D. a = b/4
Answer: B
49. The frequency range for satellite communication is
A. 3 to 30 kHz
B. 300 to 3000 kHz
C. 3000 to 30000 MHz
D. 30000 to 300000 MHz
Answer: C
50. A loop antenna is a commonly used for
A. radar
B. direction finding
C. satellite communication
D. all of the above
Answer: B
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ELECTRONICS AND COMMUNICATION ENGINEERING IMPORTANT MCQ-MATERIALS AND COMPONENTS
ELECTRICAL ENGINEERING-THREE PHASE A.C. CIRCUITS (PART ONE)

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