﻿ Medical Entrance Exam Question and Answers | Communication Systems - Zigya

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# Communication Systems

#### Multiple Choice Questions

1.

Two sources of sound placed close to each other, are emitting progressive waves given by
y1 = 4sin 600π t and y2 = 5 sin 608πt

An observer located near these two sources of sound will hear

•  4 beats per second  with intensity ratio 25: 16 between waxing and waning

• 8 beats per second with intensity ratio 25:16 between  waxing and waning

• 8 beats per second with intensity ratio 81:1 between waxing and waning

• 8 beats per second with intensity ratio 81:1 between waxing and waning

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2.

A source emits electromagnetic waves of wavelength 3m. One beam reaches the observer directly and other after reflection from a water surface, travelling 1.5 m extra distance and with an intensity reduced to 1/4 as compared to intensity due to the direct beam alone. The resultant intensity will be.

• (1/4) fold

• (3/4) fold

• (5/4) fold

• (9/4) fold

3.

A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of

• 1000

• 10000

• 10

• 100

4.

What maximum frequency can be reflected from ionosphere?

• 5 MHz

• 6 GHz

• 5 KHz

• 500 MHz

5.

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

6.

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.

7.

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.

8.

For satellite communication which wave is used

• Space wave

• Sky wave

• Ground wave

• Microwave

9.

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

10.

Long distance communication between two point or earth is achieved by

• Space wave communication

• Sky wave communication

• Satellite wave communication

• Line of sight transmission