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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 1
21.
As the frequency increases, the absorption of ground wave by earth's surface
decreases
increases
remains the same
either (a) or (c)
Answer: Option
Explanation:

Because of this reason ground waves can be used for frequencies upto about 1600 kHz only.

22.
The velocity of sound waves in air
is constant at all temperatures
varies directly as temperature
varies inversely as absolute temperature
varies directly as square root of absolute temperature
Answer: Option
Explanation:

v ∝ T.

23.
The range of a cordless telephone is about
1000 m
500 m
100 m
10 m
Answer: Option
Explanation:

The range depends on quality of instrument and is about 100 m.

24.
An earth mat for a communication tower consists of
one or two radials extending from base of tower at a depth of about 5 cm below ground
a large number of radials extending from base of tower at a depth of about 3 m
a large number of radials extending from base of tower at a depth of about 30 cm
none of the above
Answer: Option
Explanation:

The number of radials is large and depth is about 30 cm.

25.
Degaussing in a picture tube means
Adding magnetism in mask and mounting frame
Removing residual magnetism in mask, shield etc...
Increasing resistance of coils to decrease time constant
Decreasing resistance of coils to increase time constant.
Answer: Option
Explanation:

Since gauss is a unit of magnetic flux, degaussing means removal of magnetism.

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