Tuesday, September 1, 2020

Chapter 3 : Electromagnetism- Page 9

Chapter 3 : Electromagnetism

81. An antenna, when radiating, has a highly directional radiation pattern. When the antenna is receiving, its radiation pattern

A. is the same
B. exhibits no directivity at all
C. is more directive
D. is less directive

... Answer is (A)



82. The capacitance per unit length and the characteristic impedance of a lossless transmission line are C and Zo respectively. The velocity of a travelling wave on the transmission line is

A. Z₀ / C
B. C/Z₀
C. Z₀C
D. 1 / (Z₀C)

... Answer is (D)


83. The maximum usable frequency of an ionospheric layer at 60? incidence and with 8 MHz critical frequency is

A. 16 MHz
B. 1 6 / √3  MHz
C. 8 MHz
D. about 6.93 MHz

... Answer is (B)



84. An air filled rectangular waveguide has dimensions 6cm x 4cm. The cut off frequency for TE₁₀ is

A. 25 MHz
B. 5 GHz
C. 2.5 GHz
D. 25 GHz

  ... Answer is (C)


85. Sparking occurs when a load is switched off because the circuit has high
Answer is (A)


86. According to Lenz's law, the direction of induced emf and hence current
always opposes the cause producing it
B. depends on whether the coil is wound with a right or left-hand spiral.

may be found by the right-hand rule
D. is always determined by the rate of cutting flux

  ... Answer is (A)



87. When electromagnetic waves are reflected at an angle from a wall, their wavelength along the wall is

A. shortened because the Doppler effect
B. greater than in the actual direction of progapation.

the same as in free space
D. the same as the wavelength perpendicular to the wall

... Answer is (B)


88.. Transmission of power to a load over a transmission line achieves optimum value when standing-wave ratio (SWR) becomes

A. 2 : 1
B. 1 : 2
C. 1 : 1
D. 1 :√2

... Answer is (C)


89. The average noise temperature of earth, as viewed from space, is

A. 254K
C. 100K
D. 500⁰K
  ... Answer is (A)


90.  A circular loop has its radius increasing at a rate of 2 m/s. The loop is placed perpendicular to a constant magnetic field of 0.1 Wb/m2. When radius of the loop is 2 m, the emf induced in the loop will be

A. 0.8 𝜋V
B. 0.4
C. 0.2 𝜋V
D. zero

  ... Answer is (A)



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