# Electronics and Communication Engineering - Electromagnetic Field Theory

1.

A material has conductivity of 10-2 mho/m and a relative permittivity of 4. The frequency at which conduction current in the medium is equal to displacement current is

 A. 45 MHz B. 90 MHz C. 450 MHz D. 900 MHz

Explanation:

Conduction current density J = wD

J = σE σE = ωD = 2p fD 2.

A transmission line is feeding 1 watt of power to a horn antenna having a gain of 10 dB. The antenna is matched to the transmission line. The total power radiated by the horn antenna into the free space is

 A. 10 watt B. 1 watt C. 0.1 watt D. 0.01 watt

Explanation:

Pradiated = Gain of Antenna x Input power = G.I 10 log1010 . 1 10 watt.

3.

An end fire array consisting of several half-wave lengths of directive gain 40, then find the width of major lobe

 A. 60 B. 50 C. 51.25 D. None of the above

Explanation: .

4.

A uniform plane EM wave incident normally on a plane surface of a dielectric material is reflected with a VSWR of 3. What percentage of incident power that is reflected?

 A. 10% B. 25% C. 50% D. 75%

Explanation: Preflected = |δ|2 Pincident |δ|2 = 0.25 .

5.

Poynting vector is associated with which of the following?

 A. Power flow in electromagnetic B. Flux in magnetic field C. Charge in electrostatic field D. Current in electrostatic field