Multiple Choice QuestionsA sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of
1000
10000
10
100
What maximum frequency can be reflected from ionosphere?
5 MHz
6 GHz
5 KHz
500 MHz
A.
5 MHz
The ionosphere extends from a height of 80 km to 300 km. The refractive index of ionosphere is less than its free space value. That is, it behaves as a rarer medium. As we go deep into the ionosphere, the refractive index keeps on decreasing. The bending of beam (away from the normal) will continue till it reaches critical angle after which it will be reflected back. The different points on earth receive signals reflected from different depths of the ionosphere. There is a critical frequency f, (S to 100 MHz) beyond which the waves cross the ionosphere and do not return back to earth.
A hemisphere is positively charged uniformly. The electric field at a point on a diameter away from the centre is directed
perpendicular to the diameter
parallel to the diameter
at an angle tilted towards the diameter
at an angle tilted away from the diameter
Assertion: Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals.
Reason: The state of ionosphere varies from hour to hour, day to day and season to season.
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Assertion: Short wave communication over long distance is not possible via ground waves.
Reason: The ground waves can bend round the corners ofthe objects on earth.
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
If modulation index is 1/2 and power of carrier wave is 2 W. Then what will be the total power in modulated wave?
0.5 W
1 W
0.25 W
2.25 W
Long distance communication between two point or earth is achieved by
Space wave communication
Sky wave communication
Satellite wave communication
Line of sight transmission
Assertion: In a communication system based on amplitude modulation the modulation index is kept <1.
Reason: It ensures minimum distortion of signal.
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Voltage of modulating wave of 5 V with 10 MHz frequency was superimposed on carrier wave of frequency 20 MHz and voltage 20 V then the modulation index is
0.25
1.25
2.43
64.0
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