# Electronics and Communication Engineering - Electromagnetic Field Theory

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

Explanation:

Loss tangent .

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

Explanation:

l < λ/4, ZL = 0 , if Zd comes +j kZC then inductive,

If Zd comes -j kZC then capacitive.

For 0 ≤ l ≤ 1/4, λ ≤ l ≤ 3λ/4 will be inductive. 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

Explanation:

Distance = 0.4 [ht + hr] metre.

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

Explanation:

VSWR = 100.6 5.

The refractive index of E layer at frequency of 81 N

 A. 0 B. ∞ C. 1 D. 0.5 