# Online Electronics and Communication Engineering Test - Electromagnetic Field Theory Test

Instruction:

• This is a FREE online test. DO NOT pay money to anyone to attend this test.
• Total number of questions : 20.
• Time alloted : 30 minutes.
• Each question carry 1 mark, no negative marks.
• DO NOT refresh the page.
• All the best :-).

1.

Beamwidth (between first nulls) will be for an antenna at 3 MHz with directivity of 100

A.
 140°
B.
 70°
C.
 210°
D.
 60°

Explanation:

.

2.

In case of static electric field Maxwell's divergence equation states that:

A.
 ∇ . = 1/r
B.
 ∇ . = r/ε0
C.
 ∇ . = εr
D.
 ∇ . = r

3.

Which one is correct option?

A.
 TEM mode exist in free space of infinite boundary
B.
 TEM mode exist in two conductor pattern system for finite-boundary
C.
 TEM mode exist in waveguide only
D.
 Both (a) and (b)

4.

The electric flux and field intensity inside a conducting sphere is

A.
 minimum
B.
 maximum
C.
 uniform
D.
 zero

5.

For a plane good conductor, skin depth varies

A.
 directly as square root of permeability
B.
 directly as square root of frequency
C.
 inversely as permittivity
D.
 inversely as square root of conductivity

6.

For broadside array, maxima will be obtain at

A.
 90°, 270°
B.
 180°
C.
 45°
D.
 at any angle

7.

The phase velocity in a transmission line is

A.
B.
 v = LC
C.
 v = LC
D.

8.

The length of a λ/2 antenna in feet is given by the relation

A.
B.
C.
D.

9.

D-layer extends approximately from

A.
 50 to 90 km
B.
 20 to 50 km
C.
 90 to 110 km
D.
 up to 50 km

10.

What is the characteristic impedance Z0 of a line having R, inductance L, capacitance C and conductance G?

A.
B.
C.
D.

11.

For a hollow waveguide, the axial current must necessarily be

A.
 combination of conduction and displacement current
B.
 conduction current only
C.
 time varying conduction current and displacement current
D.
 displacement current only

12.

Antenna beamwidth is

A.
 measure of directivity
B.
 measure of angle
C.
D.
 measure of power pattern

13.

Which of the following is high frequency transmission line?

A.
 An impedance transformer
B.
 Frequency compensator
C.
 Flying resistor
D.
 None of the above

14.

Frequencies in the UHF range propagate by means of

A.
 space wave
B.
 surface waves
C.
 sky waves
D.
 ground waves

15.

Microwave signals follow the curvature of the earth and the phenomenon

A.
 tropospheric scatter
B.
C.
 duct propagation
D.
 none

16.

A.
 line of sight communication
B.
 ionospheric propagation
C.
 ground wave
D.
 medium wave

17.

The discone antenna is

A.
 a useful direction finding antenna
B.
 used as a radar receiving antenna
C.
 useful as a UHF receiving antenna
D.
 circular polarized like other circularly antenna

18.

The dimension of flux density is

A.
 MT-1Q-1
B.
 MT-2
C.
 MT1Q1
D.
 MT-1Q-2

19.

Poynting vector signifies which of the following?

A.
 Power density vector producing electrostatic field
B.
 Power density vector producing electromagnetic field
C.
 Current density vector producing electrostatic field
D.
 Current density vector producing electromagnetic field

20.

An antenna is considered to be in free space where its height above the ground is

A.
 λ
B.
 2λ
C.
 less than 3λ
D.
 more than 5λ