+2 Physics Unit 10 - Communication Systems

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Prepared by P. ILAIYARAJA M. Sc.,B. Ed., PG ASST IN PHYSICS , GHSS, PANCHANATHIKKULAM EAST, NAGAI DT.
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Questions and Answers
• 1.

The main purpose of modulation is to

• A.

transmit low frequency information over long distances efficiently

• B.

Produce side bands

• C.

Acquire wave shaping of the carrier wave

• D.

Combine two waves of different frequencies

Correct Answer
A. transmit low frequency information over long distances efficiently
Explanation
Modulation is the process of encoding information onto a carrier wave for transmission. The main purpose of modulation is to efficiently transmit low frequency information over long distances. By modulating the carrier wave with the low frequency signal, the information can be transmitted more effectively and with less loss over long distances. This is because low frequency signals have a longer wavelength and are more susceptible to attenuation, so modulation helps to overcome these challenges and ensure the information is transmitted efficiently.

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• 2.

In amplitude modulation

• A.

The amplitude of the carrier wave varies in accordance with the amplitude of the modulating signal.

• B.

The amplitude of the carrier wave remains constant

• C.

The amplitude of the carrier varies in accordance with the frequency of the modulating signal

• D.

Modulating frequency lies in the audio range

Correct Answer
A. The amplitude of the carrier wave varies in accordance with the amplitude of the modulating signal.
Explanation
In amplitude modulation, the amplitude of the carrier wave varies in accordance with the amplitude of the modulating signal. This means that as the modulating signal's amplitude increases or decreases, the amplitude of the carrier wave will also increase or decrease accordingly. This variation in amplitude allows the modulating signal to be carried by the carrier wave, resulting in the transmission of information. The other options are incorrect because they do not accurately describe the relationship between the carrier wave and the modulating signal in amplitude modulation.

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• 3.

In amplitude modulation, the band width is

• A.

Twice the signal frequency

• B.

Thrice the signal frequency

• C.

Four times the signal frequency

• D.

Equal to the signal frequency

Correct Answer
A. Twice the signal frequency
Explanation
In amplitude modulation, the band width is twice the signal frequency because in this modulation technique, the bandwidth is determined by the highest frequency component in the modulating signal. Since the modulating signal is multiplied with a carrier signal, the sidebands are created at frequencies above and below the carrier frequency. The highest frequency component in the modulating signal determines the width of these sidebands, which is why the bandwidth is twice the signal frequency.

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• 4.

In phase modulation

• A.

Both the phase and the frequency of the carrier wave varies.

• B.

There is no change in the frequency and phase of the carrier wave

• C.

Only the phase of the carrier wave varies

• D.

Only the frequency of the carrier wave varies.

Correct Answer
A. Both the phase and the frequency of the carrier wave varies.
Explanation
In phase modulation, both the phase and the frequency of the carrier wave vary. This means that as the information signal changes, the phase and frequency of the carrier wave also change accordingly. This modulation technique allows for the encoding of digital or analog signals onto the carrier wave, making it suitable for various communication applications. By varying both the phase and frequency, phase modulation ensures efficient transmission and accurate reception of the modulated signal.

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• 5.

The RF channel in a radio transmitter produces

• A.

High frequency carrier waves

• B.

both audio signal and high frequency carrier waves

• C.

Low frequency carrier waves.

• D.

Audio signals

Correct Answer
A. High frequency carrier waves
Explanation
The RF channel in a radio transmitter produces high frequency carrier waves. These carrier waves are used to carry the audio signals that are being transmitted. The high frequency allows for the efficient transmission of the audio signals over long distances. By modulating the carrier waves with the audio signals, the radio transmitter is able to transmit the audio signals to a receiver, which can then demodulate the carrier waves to reproduce the original audio signal.

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• 6.

The purpose of dividing each frame into two fields so as to transmit 50 views of the picture per second is

• A.

To avoid flicker in the picture

• B.

The fact that handling of higher frequencies is easier

• C.

that 50 Hz is the power line frequency in India

• D.

To avoid unwanted noises in the signals

Correct Answer
A. To avoid flicker in the picture
Explanation
Dividing each frame into two fields helps to avoid flicker in the picture. Flicker occurs when the image on the screen refreshes at a rate that is too slow for the human eye to perceive as continuous motion. By transmitting 50 views of the picture per second, the frame rate is increased, reducing the flicker effect and creating a smoother viewing experience.

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• 7.

Printed documents to be transmitted by fax are converted into electrical signals by the process of

• A.

Scanning

• B.

modulation

• C.

Light variation

• D.

Reflection

Correct Answer
A. Scanning
Explanation
Scanning is the process of converting printed documents into electrical signals by capturing the image or text using a scanner. This process involves moving a light source across the document and detecting the reflected light to create a digital representation of the document. This digital representation is then transmitted as electrical signals through the fax machine, allowing the recipient to receive a printed copy of the document.

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• 8.

High frequency waves follow

• A.

Ionospheric propagation

• B.

The curvature of the earth

• C.

The ground wave propagation

• D.

The line of sight direction

Correct Answer
A. Ionospheric propagation
Explanation
High frequency waves follow ionospheric propagation because the ionosphere, a layer of the Earth's atmosphere, can reflect and refract these waves. This allows them to travel long distances by bouncing off the ionosphere. The other options, such as the curvature of the Earth, ground wave propagation, and line of sight direction, are not specific to high frequency waves and do not explain their ability to travel long distances.

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• Current Version
• Mar 17, 2023
Quiz Edited by
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• Dec 08, 2013
Quiz Created by
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