### Electronics and Communication Engineering - Electromagnetic Field Theory MCQs Part 12

1.Tropospheric scatter is used with frequencies in the

A. HF
B. VHF
C. UHF
D. VLF

2.A Yagi antenna has a driven antenna

A. only
B. with a reflector
C. with one or more directors
D. with a reflector and one or more directors

3.The minimum height of outer atmosphere is

A. 100 km
B. 150 km
C. 200 km
D. 400 km

4.An electric charge Q is placed in a dielectric medium which of the following quantities are independent of the dielectric constant ε of the medium

A. electric potential V and electric field intensity E
B. displacement density D and displacement φ
C. electric field intensity E and displacement φ
D. electric potential V and displacement φ

5.A square corner reflector is used in

C. point to point communication
D. all of the above

6.The wave in wave guide has

A. group velocity inversely proportional to wavelength
B. larger frequency than in the free space
C. diminishing wavelength than in the free space
D. larger wavelength than in the free space

7.While determining antenna height for terrestrial microwaves links, the effect of refraction from the atmosphere is taken care of by considering the effective curvature of the earth to be

A. times the radius of the earth (Re)
B. Re
C. Re
D. Re

8.A T.V. station works at 300 MHz and radiates 100 kW of power. This signal received at a distance of 200 km will be

A. a few μV/m due to attenuation by atmosphere
B. 1-5 mV due to ionospheric reflection
C. nil since propagation is line of sight
D. nil because signal fades completely at 300 MHz

9.The power gain of a half-wave dipole with respect to an isotropic radiator is

A. 2.15 db
B. 3 db
C. 4.15 db
D. 6 db

10.In an impedance smith chart, a clockwise movement along a constant resistance circle gives rise to

A. decrease in the value of reactance
B. an increase in the value of reactance
C. no change in the reactance value
D. no change in the impedance value