Electromagnetic Field Thoery - ECE Questions and Answers

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Alternating current can induce voltage because it has magnetic field which is

constant

time varying

stronger field than D.C.

closed loop nature.

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Which of the following frequencies cannot be used for reliable beyond-the-horizon terrestrial communications without repeaters?

25 kHz

15 MHz

750 MHz

12 GHz

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Maximum effective aperture (A_e)max of short dipole antenna is

1.119 λ²

0.119 λ²

1.19 λ²

1.919 λ²

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Beamwidth of an antenna depends upon

shape of radiation pattern

dimensions

wavelength

all of the above

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Tropospheric mode of propagation is used in

UHF

VLF

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The skip distance is

same for each layer

independent of frequency

independent of the state of ionisation

independent of transmitted power

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Polystyrene has a relative permittivity of 2.7. If the wave is incident at an angle θ_i of 30° from air into polystyrene, the angle of transmission will be nearly

0.2°

2°

18°

48°

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The radiation pattern of helical antenna (axial mode) is represented by

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Antenna aperture efficiency is given by