# 300+ TOP Electromagnetic Field Theory Questions and Answers pdf

## Electromagnetic Field Theory Questions :-

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

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

3. Parabolic and lens antenna used at

A. microwave frequency
B. medium frequency
C. low frequency
D. high frequency

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

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

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

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

8. In H-plane metal plate lens the travelling wave front is

A. totally retarded
B. retarded
C. accelerated
D. neither accelerated nor retarded

9. MUF is depend upon

A. electron density of the ionospheric layer
B. 11 year sun spot cycle
D. height of ionospheric layer

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

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

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

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

14. The critical frequency of ‘F’ layer is greater than 30 MHz.

A. True
B. False

15. Which of the following will increase the antenna radiation efficiency?

A. Use of larger section of conductor
B. Providing insulation on conductor
D. Any of the above

16. A waveguide operated below cut off frequency can be used as

A. phase shifter
B. an attenuator
C. an isolator
D. none

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

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

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

20. Tropospheric scatter is used with frequencies in the

A. HF
B. VHF
C. UHF
D. VLF

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

22. The minimum height of outer atmosphere is

A. 100 km
B. 150 km
C. 200 km
D. 400 km

23. A square corner reflector is used in

C. point to point communication
D. all of the above

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

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

### ELECTROMAGNETIC FIELD THEORY Questions and Answers ::

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

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

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

29. The radiation pattern of a parabola antenna is

A. omnidirectional
B. a figure of directional
C. highly directional
D. none of the above

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

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

32. The virtual height of an ionospheric layer is __________ true height

A. equal to
B. less than
C. higher than
D. no relation

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

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

35. The skip distance is the maximum distance upto which ionospheric reflection is possible.

A. True
B. False

36. Which antenna is a wideband antenna?

A. Hertz antenna
B. Marconi antenna
C. Folded dipole
D. None of the above

37. The radiation pattern of loop antenna is

A. circle
B. semicircle
C. elliptical
D. cardoid or Limacon

38. Tropospheric scatter propagation is not subject to any fading.

A. True
B. False

39. The attenuation in waveguide above to cut off frequency

A. very high
B. very low
C. zero
D. infinite

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

41. A square corner reflector is used in which of the following?

B. Point-to-point communication
D. All of the above

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

43. The static electric field in a conductor is

A. zero
B. unity
C. infinity
D. none of the above

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

45. MUF is highest in periods of greatest sunspot activity.

A. True
B. False

46. Which of the following is multiband HF receiving antenna?

A. Square loop
B. Log-periodic
C. Conical horn
D. Folded dipole

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

48. If a and b are the dimensions of waveguide then

A. a = 3b
B. a = 2b
C. a = b
D. a = b/4

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

50. A loop antenna is a commonly used for

B. direction finding
C. satellite communication
D. all of the above