Tuesday, September 1, 2020

Chapter 3 : Electromagnetism- Page 8

Chapter 3 : Electromagnetism

71. The dominant mode in a rectangular wave guide is TE₀, because this mode has

A. no magnetic field component
B. the highest cut off wavelength
C. is a wide band antenna
D. is an omni diretional antenna

... Answer is (B)



72. 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. longitudinal
B. transverse-electromagnetic
C. transverse-electric
D. transverse-magnetic

... Answer is (D)


73. As aresult 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. group velocity
B. phase velocity
C. velocity of propagation
D. normal velocity

... Answer is (B)



74. A(75 - j50)Ω load is connected to a coaxial transmission line of Z₀ = 7512, at 10 GHz. The best method of matching consists in connecting

A. a capacitance at some specific distance from the load
B. a short-circuited stub at some specific distance from the load
C. a short-circuited stub at the load
D. an inductance at the load

  ... Answer is (D)


75. The velocity factor of a transmission line
Answer is (C)


76. Short-circuited stubs are preferred to open-circuited stubs because the latter are
liable to radiate
B. incapable of giving a reactances.

more difficult to make and connect
D. made of a transmission line with a different characteristic impedance

  ... Answer is (D)



77. A transmission line whose characteristic impedance is a pure resistance

A. may not be a lossless line
B. may not be a distortion less line.

must be a lossless line
D. must be a distortionless line

... Answer is (A)


78.. Medium wave radio signals may be received at far off distance at night because

A. radio waves travel faster at night
B. ground wave attenuation is low at night
C. the sky wave is stronger at night
D. their is no fading at night

... Answer is (C)


79. A plane electromagnetic wave travelling along +z-direction, has its electric field given by Ex = 2 cos(*t) and E = 2 cos (*t + 90). The wave is

A. left circularly polarized
B. elliptically polarized
C. linearly polarized full range of mainly for straight-line applies to
D. right circularly polarized
  ... Answer is (A)


80. For a dipole antenna

the affective length equals its physical length
B. the input imepedance is independent of the location of the feed-point.

the radiation intensity is maximum along the normal to the dipole axis
D. the current distribution along its length is uniform irrespective of the length

  ... Answer is (C)



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