### Electronics and Communication Engineering - Electromagnetic Field Theory MCQs Part 1

1.ZL = 200 Ω and it is desired that Zi = 50 Ω The quarter wave transformer should have a characteristic impedance of

A. 100 Ω
B. 40 Ω
C. 10000 Ω
D. 4 Ω

2.A broadside array consisting of 200 cm wavelength with 10 half-wave dipole spacing 10 cm. And if each array element feeding with 1 amp. current and operating at same frequency then find the half power beamwidth

A. 4°
B. 2°
C. 10°
D. 15°

3.Refractive index of glass is 1.5. Find the wavelength of a beam of light with a frequency of 1014 Hz in glass. Assume velocity of light is 3 x 108 m/sec in vacuum.

A. 4 μm
B. 3 μm
C. 2 μm
D. 1 μm

4.The function f(x - vot) represent which of the following?

A. A stationary wave
B. A wave motion in forward direction
C. A wave motion in reverse direction
D. None of the above

5.A broadside array operating at 100 cm wavelength consist of 4 half-wave dipoles spaced 50 cm apart. Each element carries radio frequency current in the same phase and of magnitude 0.5 A. The radiated power will be

A. 196 W
B. 73 W
C. 36.5 W
D. 18.25 W

6.The input impedance of short-circuited line of length l where λ/4 < l < λ/2, is

A. resistive
B. inductive
C. capacitive
D. none of the above

7.A wave is propagated in a waveguide at frequency of 9 GHz and separation is 2 cm between walls find cut off wavelength for dominant mode.

A. 4 cm
B. 1 cm
C. 2 cm
D. 8 cm

8.Find the radiation resistance of an antenna of length λ/10 meter?

A. 8 Ω
B. 780 Ω
C. 7.8 Ω
D. 78 Ω

9.Charge needed within a unit sphere centred at the origin for producing a potential field,

A. 12 pc
B. 60 pc
C. 120 pc
D. 180 pc

10.A rectangular metal waveguide filled with a dielectric of relative permittivity εr = 4, has the inside dimensions 3 x 1.2 cm, the cut off frequency for the dominant mode is

A. 2.5 GHz
B. 5 GHz
C. 10 GHz
D. 12.5 GHz