In Physics, communication means the transmission of information. This chapter does not have many concepts and the problems asked in the examination also does not have many varieties. Candidates who are preparing this chapter should focus on gaining the knowledge of basic concepts, formula, and bandwidth of signals. Also, you should have a clear idea about the functions of all the equipment.

  • The common questions from this chapter are based on Transmitter, Modulation, Bandwidths, etc. Check JEE Main Physics Syllabus
  • The weightage of this section is 3 to 4%. Only one question can be expected from this section and that could be direct question.

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For the transmission of information from one place to another, there are various essential elements of communication that are all discussed in this article. The solved examples will help you in getting a clear idea about the basic concepts of the communication system for JEE Main. 

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Transmitter, Channel & Receiver

Transmitter, Channel and Receiver

Transmitter: Transmitter is used to transmit the input signal from the information source. 

Channel: Channel is defined as the medium through which the signal is sent from transmitter to receiver. 

Receiver: The receiver is used to extract the designed message signal from the received signal at the channel output.

Sample Question

Question: An antenna is a device that

  1. converts electromagnetic energy into a radio frequency signal
  2. converts radio frequency signal into electromagnetic energy
  3. converts free-space electromagnetic waves into guided electromagnetic waves and vice-versa
  4. None of these

Solution: (3)

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Bandwidth of the Signal

Bandwidth of the Signal

The difference between the maximum and minimum frequency of a signal is known as the bandwidth of that signal.

The frequency band of some important wireless communications

Service Frequency Bands
Standard AM Broadcast 540 to 1600 KHz
FM Broadcast 88 to 108 MHz
Television (VHF) 54 to 72 MHz
TV 76 to 88 MHz
VMF 174 to 216 MHz
Cellular Mobile Radio 896 to 901 MHz 840 to 935 MHz
Satellite communication  5.925 to 6.425 MHz 3.7 to 4.2 GHz

Sample Question

Question: Which mode of communication is not employed for the transmission of T.V. signals?

  1. Ground wave propagation
  2. skywave propagation
  3. space wave propagation
  4. None of these

Solution: (1)

Propagation of Electromagnetic Waves

Propagation of Electromagnetic Waves

Ground Wave Propagation: The radio waves that travel through the atmosphere following the surface of the earth are known as ground waves or surface waves. And their propagation is called as ground wave propagation or surface wave propagation.

Important points to Remember

  • The transmission of these waves becomes weaker with the increase in the frequency because more absorption of ground waves takes place at a higher frequency during the propagation through the atmosphere.
  • These waves are suitable for the low and medium frequency that is up to 2 to 3 MHz only. 
  • These waves are generally used for local band broadcasting.

SkyWave Propagation: The sky waves are radio waves that have a frequency between 2 MHz to 30 MHz.

Important points to Remember

  • The ionospheric layer acts as a reflector for a certain range of frequencies that is 3 to 30 MHz.
  • Electromagnetic waves of frequencies higher than 30 MHz penetrate the ionosphere and escape. 
  • The highest frequency of radio waves is known as critical frequency.

Space Wave Propagation: These are high-frequency radio waves. 

Important Points to Remember

  • The range of communication of space wave propagation can be increased by increasing the heights of transmitting and receiving antennas.

Sample Question

Question: Modulation is the process of superposing

  1. low-frequency audio signal on high-frequency waves
  2. low-frequency radio signal on low-frequency audio waves
  3. high-frequency audio signal on low-frequency radio waves
  4. low-frequency audio signal on low-frequency radio waves

Solution: (1)

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Concept of Modulation

Modulation 

It is the process by which input signal or modulating signal is mounted onto another signal of a high frequency which is called the carrier signal. The resultant signal is called a modulated signal. 

Amplitude modulation: In this modulation, the amplitude of the carrier is varied according to the information signals. 

Let represent carrier wave and represents the message or the modulating signal where is the angular frequency of the message signal. 

The modulated signal can be represented as

Moducation Index can be represented by 

Frequency Modulation: When the frequency of the carrier wave is changed with the change in the intensity of the modulating signal it is called frequency modulation. 

Moducation Factor or Index and Carrier Swing (CS) can be defined as

Moducation Factor, m = Maximum frequency deviation/ Modulating Frequency = , where

Also, 

Sample Questions from Communication

Previous Years Sample Questions from Communication System

1. Question: A laser beam used for carrying out surgery because it is 

  1. highly monochromatic
  2. highly coherent
  3. highly directional
  4. can be sharply focused

Solution: (1)

2. Question: The range of skywave propagation is suitable for radio- waves of frequency

  1. up to 2MHz
  2. from 2MHz to 20MHz
  3. from 2MHz to 30MHz
  4. from 2MHz to 50MHz

Solution: (3)

3. Question: Let us consider that a T.V. tower has a height of 150 m. Ff the total population covered is 50 lakh then what is the population density around the T.V. tower? The radius of the earth is 6.4×106m.

  1. 800km−2
  2. 829km−2
  3. 82.6km−2
  4. 826.6km−2

Solution: (2)

4 Question: If an FM radio receiver is tuned to 98.6 MHz broadcast station then what will be the image frequency?

  1. 111.8MHz
  2. 108MHz
  3. 121.6MHz
  4. 132MHz

Solution: (3)

5 Question: What is the phenomenon by which light travels in an optical fiber?

  1. Reflection
  2. Refraction
  3. Total internal reflection
  4. Transmission

Solution: (3)

Some Tricks to Solve Question

Tricks to Solve Question from Communication System

  • To solve the questions from this chapter have crystal clear concepts of Transmitter, transmission channel, and receiver 
  • Revise all the formulas and their condition again and again like the range of the antenna, amplitude modulated signal frequency, etc. 
  • Draw all the flow diagrams of each part of the communication system to understand the concepts better. 
  • Remember all the one-line definitions because sometimes direct questions can be solved if you know the definitions. 
  • Modulation is the process of superposing low-frequency audio signal on high-frequency waves
  • The antenna converts free-space electromagnetic waves into guided electromagnetic waves and vice-versa.
  • In JEE Main 2020, it is a concept based chapter and there are many points to memorize, hence practice is the key here for getting a good hold on this chapter.
  • Questions will be asked on the range of the antenna, modulation of waves, and the functions of the equipment used.
  • Study the concept first and then solve the questions on Communication systems.
  • Don't go through questions directly without knowing the concept.