MCQOPTIONS
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MCQOPTIONS
This section includes 248 Mcqs, each offering curated multiple-choice questions to sharpen your Electromagnetic Theory knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
Which of the following pairs of parameters and expressions is/are correctly matched? 1. Characteristic impedance ............ E/ H r 2. Power flow density ...... H 3. Displacement current in non-conducting medium ...... E H Select the correct answer using the codes given below: |
| A. | 1 alone |
| B. | 2 and 3 |
| C. | 1 and 3 |
| D. | 1 and 2 |
| Answer» B. 2 and 3 | |
| 52. |
The Q of a antenna in loaded and unloaded condition is related to |
| A. | Q |
| B. | = 2 Q |
| C. | Q |
| D. | = Q |
| Answer» E. | |
| 53. |
The wavelength of a wave with propagation constant (0.1 + j 0.2 ) m 1 is |
| A. | 10 m |
| B. | 20 m |
| C. | 30 m |
| Answer» C. 30 m | |
| 54. |
Some unknown material has a conductivity of 106 mho/m and a permeability of 4 10 7 H/m. The skin depth for the material at 1 GHz is |
| A. | 15.9 m |
| B. | 20.9 m |
| C. | 25.9 m |
| D. | 30.9 m |
| Answer» B. 20.9 m | |
| 55. |
Given that E = time and space dependent electric field intensity vector = permeability of the medium = conductivity of the medium = permittivity of the medium The electromagnetic wave equation is |
| A. | |
| Answer» B. | |
| 56. |
A (75 j 50) load is connected to coaxial transmission line of Z0 = 75 at 10 GHz the best method of matching consists in connecting |
| A. | A short circuited stub at the load |
| B. | An inductance at the load |
| C. | A capacitance at some specific distance from the load |
| D. | A short circuited stub at some specific distance from the load |
| Answer» E. | |
| 57. |
Assuming the velocity of EM waves reaching an antenna as 3 108 m/sec the length of a half wave dipole antenna required to receive a 5 MHz radio signal is |
| A. | 7.5 m |
| B. | 13 m |
| C. | 30 m |
| D. | 60 m |
| Answer» E. | |
| 58. |
A 50 lossless T.L. has a pure reactance of j 100 as its load. The VSWR in the live is |
| A. | 0 |
| B. | |
| C. | 50 |
| D. | 100 + j 100 |
| Answer» C. 50 | |
| 59. |
Consider two fields |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» E. | |
| 60. |
A piston attenuator is a |
| A. | Vane attenuator |
| B. | Waveguide below cut-off |
| C. | Mode filter |
| D. | Flap attenuator |
| Answer» C. Mode filter | |
| 61. |
A choke flange may be used to couple two waveguides |
| A. | To help in the alignment of the waveguides |
| B. | Because it is simpler than any other join |
| C. | To compensate for discontinuities at the join |
| D. | To increase the bandwidth of the system |
| Answer» D. To increase the bandwidth of the system | |
| 62. |
Which one of the following waveguide tuning components are not easily adjustable? |
| A. | Screw |
| B. | Stub |
| C. | Iris |
| D. | Plunger |
| Answer» D. Plunger | |
| 63. |
In order to couple two generators to a waveguide system without coupling them to each other, one could not use a |
| A. | Rat-race |
| B. | E-plane T |
| C. | Hybrid ring |
| D. | Magic T |
| Answer» C. Hybrid ring | |
| 64. |
The Gain of an antenna with a circular aperture of diameter 3 m at a frequency 5 GHz is |
| A. | 22649 |
| B. | 26469 |
| C. | 24649 |
| D. | None of these |
| Answer» D. None of these | |
| 65. |
The radiation resistance of an antenna is 72 , and loss resistance is 8 . What is the directivity if the power gain is 16? |
| A. | 17.78 |
| B. | 14.4 |
| C. | 16 |
| D. | None of these |
| Answer» B. 14.4 | |
| 66. |
Frequencies in the UHF range normally propagate by means of |
| A. | Ground waves |
| B. | Sky waves |
| C. | Surface waves |
| D. | Space waves |
| Answer» E. | |
| 67. |
A transmitting antenna radiates 251 watt isotropically. A receiving antenna locating 100 m away from the transmitting antenna has an effective aperture of 500 cm |
| A. | 10 W |
| B. | 20 W |
| C. | 1 W |
| D. | 100 W |
| Answer» E. | |
| 68. |
In a uniform linear array, four isotropic radiating elements are spaced /4 apart.The progressive phase shift between the elements required for forming the main beam at 60 of the end fire array is |
| A. | radians |
| B. | <table><tr><td rowspan="2"> </td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center> </center></td><td rowspan="2"> radians </td></tr><tr><td style="text-align: center;">2</td></tr></table> |
| C. | <table><tr><td rowspan="2"> </td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center> </center></td><td rowspan="2"> radians </td></tr><tr><td style="text-align: center;">4</td></tr></table> |
| D. | <table><tr><td rowspan="2"> </td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center> </center></td><td rowspan="2"> radians </td></tr><tr><td style="text-align: center;">8</td></tr></table> |
| Answer» D. <table><tr><td rowspan="2"> </td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center> </center></td><td rowspan="2"> radians </td></tr><tr><td style="text-align: center;">8</td></tr></table> | |
| 69. |
In a broadside array of 20 isotropic radiators, equally spaced at distance of /2, the beamwidth of the first nulls is |
| A. | 11.46 |
| B. | 5.73 |
| C. | 10.46 |
| D. | None of these |
| Answer» B. 5.73 | |
| 70. |
A (75 j50)- load is connected to a coaxial transmission line of Z0 = 75 . at 10 GHz. The best method of matching consists in connecting |
| A. | A short-circuited stub at the load |
| B. | An inductance at the load |
| C. | A capacitance at some specific distance from the load |
| D. | A short-circuited stub at some specific distance from the load |
| Answer» E. | |
| 71. |
A plane wave is characterized by |
| A. | Linearly polarized |
| B. | Circularly polarized |
| C. | Elliptically polarized |
| D. | Unpolarized |
| Answer» D. Unpolarized | |
| 72. |
For transmission-line load matching over a range of frequencies, it is best to use a |
| A. | Balun |
| B. | Broadband directional coupler |
| C. | Double stub |
| D. | Single stub of adjustable position |
| Answer» D. Single stub of adjustable position | |
| 73. |
Short-circuited stubs are preferred to open-circuited stubs because the latter are |
| A. | More difficult to make and connect |
| B. | Made of a transmission line with a different characteristic impedance |
| C. | Liable to radiate |
| D. | Incapable of giving a full range of reactances |
| Answer» D. Incapable of giving a full range of reactances | |
| 74. |
Indicate which of the following frequencies cannot be used for reliable beyond the horizon terrestrial communications without repeaters? |
| A. | 20 kHz |
| B. | 15 MHz |
| C. | 900 MHz |
| D. | 12 GHz |
| Answer» E. | |
| 75. |
Indicate which one of the following terms applies to troposcatter propagation |
| A. | SIDs |
| B. | Fading |
| C. | Atmospheric storms |
| D. | Faraday rotation |
| Answer» C. Atmospheric storms | |
| 76. |
To couple a coaxial line to a parallel-wire line, it is best to use a |
| A. | Slotted line |
| B. | Balun |
| C. | Directional Coupler |
| D. | Quarter-wave transformer |
| Answer» C. Directional Coupler | |
| 77. |
A range of microwave frequencies more easily passed by the atmosphere than are the others is called a |
| A. | Windows |
| B. | Critical frequency |
| C. | Gyro frequency range |
| D. | Resonance in the atmosphere |
| Answer» B. Critical frequency | |
| 78. |
A ship-to-ship communications system is plagued by fading. The best solution seems to be the use of |
| A. | A more directional antenna |
| B. | A broadband antenna |
| C. | Frequency diversity |
| D. | Space diversity |
| Answer» D. Space diversity | |
| 79. |
High-frequency waves are |
| A. | Absorbed by the F2 layer |
| B. | Reflected by the D layer |
| C. | Capable of use for long-distance communications on the moon |
| D. | Affected by the solar cycle |
| Answer» E. | |
| 80. |
Top loading is sometimes used with an antenna in order to increase its |
| A. | Effective height |
| B. | Bandwidth |
| C. | Beamwidth |
| D. | Input capacitance |
| Answer» B. Bandwidth | |
| 81. |
One of the following is not an omnidirectional antenna |
| A. | Half-wave dipole |
| B. | Log-periodic |
| C. | Discone |
| D. | Marconi |
| Answer» C. Discone | |
| 82. |
Indicate which of the following reasons for using a counterpoise with antennas is false? |
| A. | Impossibility of a good ground connection |
| B. | Protection of personnel working underneath |
| C. | Provision of an earth for the antenna |
| D. | Rockiness of the ground itself |
| Answer» C. Provision of an earth for the antenna | |
| 83. |
One of the following is very useful as a multiband HF receiving antenna. This is the |
| A. | Conical horn |
| B. | Folded dipole |
| C. | Log-periodic |
| D. | Square loop |
| Answer» D. Square loop | |
| 84. |
An antenna that is circularly polarized is the |
| A. | Helical |
| B. | Small circular loop |
| C. | Parabolic reflector |
| D. | Yagi-Uda |
| Answer» B. Small circular loop | |
| 85. |
Which one of the following terms does not apply to the Yagi-Uda array? |
| A. | Good bandwidth |
| B. | Parasitic elements |
| C. | Folded dipole |
| D. | High gain |
| Answer» E. | |
| 86. |
A signal propagated in a waveguide has a full wave of electric intensity change between the two further walls, and no component of the electric field in the direction of propagation. The mode is |
| A. | TE1.1 |
| B. | TE1.0 |
| C. | TM2.2 |
| D. | TE2.0 |
| Answer» E. | |
| 87. |
The main difference between the operation of transmission lines and waveguides is that |
| A. | The latter are not distributed, like transmission lines |
| B. | The former can use stubs and quarter-wave transformers, unlike the latter |
| C. | Transmission lines use the principal mode of propagation, and therefore do not suffer from low-frequency cutoffs |
| D. | Terms such as impedance matching and standing wave ratio cannot be applied to waveguides |
| Answer» D. Terms such as impedance matching and standing wave ratio cannot be applied to waveguides | |
| 88. |
The wavelength of a wave in a waveguide |
| A. | Is greater than in free space |
| B. | Depends only on the waveguide dimensions and the free-space wavelength |
| C. | Is inversely proportional to the phase velocity |
| D. | Is directly proportional to the group velocity |
| Answer» B. Depends only on the waveguide dimensions and the free-space wavelength | |
| 89. |
Indicate the false statement. When the free-space wavelength of a signal equals the cutoff wavelength of the guide |
| A. | The group velocity of the signal becomes zero |
| B. | The phase velocity of the signal becomes infinite |
| C. | The characteristic impedance of the guide becomes infinite |
| D. | The wavelength within the waveguide becomes infinite |
| Answer» D. The wavelength within the waveguide becomes infinite | |
| 90. |
In electromagnetic waves, polarization |
| A. | Is caused by reflection |
| B. | Is due to the transverse nature of the waves |
| C. | Results from the longitudinal nature of the waves |
| D. | Is always vertical in an isotropic medium |
| Answer» C. Results from the longitudinal nature of the waves | |
| 91. |
As electromagnetic waves travel in free space, only one of the following can happen to them |
| A. | Absorption |
| B. | Attenuation |
| C. | Refraction |
| D. | Reflection |
| Answer» C. Refraction | |
| 92. |
The ground wave eventually disappears, as one moves away from the transmitter, because of |
| A. | Interference from the sky wave |
| B. | Loss of line-of-sight conditions |
| C. | Maximum single-hop distance limitation |
| D. | Tilting |
| Answer» E. | |
| 93. |
Tropospheric scatter is used with frequencies in the following range |
| A. | HF |
| B. | VHF |
| C. | UHF |
| D. | VLF |
| Answer» D. VLF | |
| 94. |
A half wave dipole capable of radiating 1 kW and has 2.15 dB over a isotropic antenna. How much power must be delivered to the isotropic omnidirectional antenna, to match the field strength of directional antenna? |
| A. | 1264.7 watt |
| B. | 1441 watt |
| C. | 1364.7 watt |
| D. | 1641 watt |
| Answer» E. | |
| 95. |
As a result of reflections from a plane conducting wall, electromagnetic waves acquire an apparent velocity greater than the velocity of light in space. This is called the |
| A. | Velocity of propagation |
| B. | Normal velocity |
| C. | Group velocity |
| D. | Phase velocity |
| Answer» E. | |
| 96. |
When a particular mode is excited in a waveguide, there appears an extra electric component, in the direction of propagation. The resulting mode is |
| A. | Transverse-electric |
| B. | Transverse-magnetic |
| C. | Longitudinal |
| D. | Transverse-electromagnetic |
| Answer» C. Longitudinal | |
| 97. |
TEM wave has proper density 1.2 watt/m |
| A. | 22.85 V/m |
| B. | 39.57 V/m |
| C. | 13.19 V/m |
| D. | None of these |
| Answer» B. 39.57 V/m | |
| 98. |
Waveguides are used mainly for microwave signals because |
| A. | They depend on straight-line propagation which applies to microwaves only |
| B. | Losses would be too heavy at lower frequencies |
| C. | There are no generators powerful enough to excise them at lower frequencies |
| D. | They would be too bulky at lower frequencies |
| Answer» E. | |
| 99. |
Cassegrain feed is used with a parabolic reflector to |
| A. | Increase the gain of the system |
| B. | Increase the beamwidth of the system |
| C. | Reduce the size of the main reflector |
| D. | Allow the feed to be placed at a convenient point |
| Answer» E. | |
| 100. |
Indicate which one of the following reasons for the use of an earth mat with antennas is false |
| A. | Impossibility of a good ground connection |
| B. | Provision of an earth for the antenna |
| C. | Protection of personnel working underneath |
| D. | Improvement of the radiation pattern of the antenna |
| Answer» D. Improvement of the radiation pattern of the antenna | |