Electromagnetic Field Theory — Part 1 MCQs with Explanations

Option A: Radar Loop antennas are not commonly used for radar systems. Radar systems typically use high-gain antennas such as parabolic reflectors or phased arrays to achieve precise directional transmission and reception. Option B: Direction finding Loop antennas are widely used for direction finding. Their ability to detect the direction of an incoming signal based on variations in induced voltage makes them suitable for this application. This is a key characteristic of loop antennas. Option C: Satellite communication Loop antennas are not ideal for satellite communication. Satellite communication generally requires antennas with high gain and wide coverage, such as parabolic dish antennas, to handle the high-frequency signals and large distances involved. Option D: All of the above While loop antennas are useful for direction finding, they are not commonly used for radar or satellite communication. Thus, this option is incorrect. Conclusion: The correct answer is Option B: Direction finding , as loop antennas are specifically designed and effectively used for detecting the direction of incoming signals.

Option A: Scalar The divergence of a vector field is a scalar quantity; however, the curl of a vector field is not a scalar. The curl represents a rotational effect, which requires more than a single value to describe. Option B: Vector The curl of a vector field is indeed another vector. It represents the rotation or circulation of the vector field at a point and is defined by a vector perpendicular to the plane of rotation, with its magnitude indicating the strength of the rotation. Option C: Unit vector A unit vector has a magnitude of one and represents direction. The curl of a vector field is not necessarily a unit vector; it depends on the magnitude of the rotation within the field. Option D: None of the above This option is incorrect because the curl of a vector field is not undefined. It is explicitly a vector quantity and is described by standard mathematical operations. Conclusion: The correct answer is Option B: Vector , as the curl of a vector is another vector that describes the rotation of the field.

Option A: Hertz antenna The Hertz antenna, also known as a dipole antenna, operates efficiently over a narrow frequency range. It is not considered a wideband antenna since its bandwidth is limited. Option B: Marconi antenna The Marconi antenna is a type of monopole antenna typically used for narrowband applications. It is not designed to handle a wide range of frequencies, making it unsuitable as a wideband antenna. Option C: Folded dipole The folded dipole is a type of wideband antenna. Its construction allows it to operate over a broader frequency range compared to standard dipole antennas. This characteristic makes it suitable for applications requiring wideband operation. Option D: None of the above This option is incorrect because the folded dipole antenna is explicitly a wideband antenna. Therefore, this statement does not apply. Conclusion: The correct answer is Option C: Folded dipole , as it is specifically designed to function as a wideband antenna.

Retardation is the correct answer to “The potential that appears at a point in space due to the current which caused it is called potential”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

400 km is the correct answer to “The minimum height of outer atmosphere is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Highly directional is the correct answer to “The radiation pattern of a parabola antenna is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Higher than is the correct answer to “The virtual height of an ionospheric layer is __________ true height”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Vertical grounded wire type is the correct answer to “The transmitting antennas for lower frequencies (below 500 kHz) are generally”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Top loading of antenna is the correct answer to “Which of the following will increase the antenna radiation efficiency”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

The impedance of one is the complex conjugate of the other is the correct answer to “According to maximum power transfer theorem, the maximum power is absorbed by one network from another network when”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

False is the correct answer to “Tropospheric scatter propagation is not subject to any fading.”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

All of the above is the correct answer to “A square corner reflector is used in which of the following”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

An increase in the value of reactance is the correct answer to “In an impedance smith chart, a clockwise movement along a constant resistance circle gives rise to”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Distance of the point from the antenna is the correct answer to “In case of surface waves the field strength at a point is directly proportional to”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Figure of eight is the correct answer to “The radiation pattern of Hertzian dipole in the plane perpendicular to dipole is a”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

A standing wave which is not progressing is the correct answer to “In a perfect conductor the incident and reflected wave combine to produce”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Balun is the correct answer to “It is best to use for coupling a coaxial line to a parallel wire transmission line.”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Retarded is the correct answer to “In H-plane metal plate lens the travelling wave front is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Log-periodic is the correct answer to “Which of the following is multiband HF receiving antenna”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

1.5 is the correct answer to “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”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

False is the correct answer to “The critical frequency of ‘F’ layer is greater than 30 MHz.”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

At waveguide can be coupled to a coaxial cable is the correct answer to “Which of the following statement regarding waveguides is incorrect”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Hollow rectangular conducting tube through which electromagnetic waves can be propagat-ed is the correct answer to “A rectangular waveguide is a”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

UHF is the correct answer to “Tropospheric scatter is used with frequencies in the”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

With a reflector and one or more directors is the correct answer to “A Yagi antenna has a driven antenna”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Front to back ratio is the correct answer to “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”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

3000 to 30000 MHz is the correct answer to “The frequency range for satellite communication is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Zero is the correct answer to “The static electric field in a conductor is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

False is the correct answer to “The skip distance is the maximum distance upto which ionospheric reflection is possible.”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Microwave frequency is the correct answer to “Parabolic and lens antenna used at”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Received frequency by receiver is the correct answer to “MUF is depend upon”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Cardoid or Limacon is the correct answer to “The radiation pattern of loop antenna is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

The value of current is the correct answer to “When a current carrying conductor is brought into magnetic field, the force that moves the conductor depends upon”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

a = 2b is the correct answer to “If a and b are the dimensions of waveguide then”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Refraction is the correct answer to “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 __________ .”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Charge per unit area becomes very high for lightening to discharge is the correct answer to “Due to which of the following reasons a lightning conductor on top of a building is made into a pointed spike”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

None of the above is the correct answer to “The useful magnetic flux obtainable from any closed surface is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Polarisation is the correct answer to “When the phase velocity of an EM wave depends on frequency in any medium the phenomenon is called”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Passive satellite is the correct answer to “A satellite that simply reflect back the signals from one region of the earth to the other region is known as”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.

Narrow bandwidth is the correct answer to “The main disadvantage of the two-hole directional coupler is”. This question is standard in competitive examination syllabi for Electromagnetic Field Theory.