### Electronics and Communication Engineering - Electromagnetic Field Theory MCQs Part 3

1.Distilled water at 25°C is characterized by σ = 1.7 x 10-4 mho/m and ε = 78 ε0 at a frequency of 3 GHz. Its loss tangent is (ε = 10-9/36p F/m)

A. 1.3 x 10-5
B. 1.3 x 10-3
C. 1.7 x 10-4/78
D. 1.7 x l0-4/78ε0

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

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

3.If the height of transmitting and receiving antenna in a LOS system are 49 meter and a 9 meter respectively then the distance up to which communication may be possible is about

A. 40 km
B. 110 km
C. 400 km
D. 1100 km

4.In a line VSWR of a load is 6 dB. The reflection coefficient will be

A. 0.033
B. 0.33
C. 0.66
D. 3.3

5.The refractive index of E layer at frequency of 81 N

A. 0
B. ∞
C. 1
D. 0.5

6.∇ . = 0 is frequently known as

A. continuity equation for steady currents
B. Laplace equation
C. Poisson's equation
D. none of the above

7.A rhombic antenna is a

A. resonant antenna
B. non-resonant antenna
C. coupled antenna
D. none of the above

8.Which of the following relations is valid?

A. ∇ x ∇ x = ∇(∇ . ) - ∇2 A
B. ∇ x ∇ x = ∇(∇ x ) - ∇2 A
C. ∇ x ∇ x = ∇2 A - (∇)
D. none of the above

9.Diffraction of electromagnetic waves

A. may occur around the edge of a sharp obstacle
B. is caused by reflections from the ground
C. arises only with the spherical wave fronts
D. will occur when the waves pass through a large slot

10.The magnetic field intensity vector of a plane wave is given by (x, y, z, t) = 10 sin (5000t + 0.004x + 30 ), where denotes unit vector in y direction the wave is propagating with a phase velocity.

A. 5 x 104 m/sec
B. -3 x 108 m/sec
C. -1.25 x 107 m/sec
D. 3 x 108 m/sec