NCERT Solutions Class 12 Physics Chapter 15

NCERT Solutions Class 12 Physics Chapter 15 – Communication systems

The NCERT Solutions Class 12 Physics Chapter 15 are one of the best academic resources to learn about the subject. These notes include all the topics and concepts from the Central Board of Secondary Education (CBSE) syllabus. With the help of the NCERT solutions, students can prepare for CBSE exams as well as many other competitive exams like JEE and NEET. Regular practice using the notes will ensure that the students grasp this chapter and the topics covered under it. The NCERT Solutions Class 12 Physics Chapter 15 are curated by the qualified professionals and experienced teachers to help students study and prepare for the exams effectively. 

NCERT Solutions Class 12 Physics Chapter 15 Communication System encompass the basic terminologies and elements of a Communication System. Topics like propagation of electromagnetic waves, Modulation, and bandwidth of signals are covered in chapter 15 NCERT solutions class 12 Physics. Students will also learn about the production and detection of Amplitude Modulated waves. The chapter is based on the different systems used to transmit, connect, communicate and interconnect. They are classified into three areas: Media, Technology, and Application. 

Extramarks helps students to learn more effectively with revolutionising methods. In addition, it provides interactive learning through the plethora of NCERT Solutions for various other classes. The experts  past years’ questions papers analysed by experts, sample papers, important concepts, and problems from the chapter before preparing the NCERT Solutions Class 12 Physics Chapter 15. 

In addition to NCERT Solutions Class 12 Physics Chapter 15, students can refer to study material for various other subjects. Students can also refer to other revision notes and NCERT Solutions from Class 1 to class 12 for all subjects at Extramarks for improving their academic performance.

Key Topics Covered In NCERT Solutions Class 12 Physics Chapter 15

The NCERT Solutions Class 12 Physics Chapter 15 will help students practise various objective questions, reasoning questions, and questions that need to be answered in brief from the chapter. Students who wish to pursue a career in engineering or medical science must ensure that they gain in-depth knowledge and understanding by using the NCERT Solutions provided by Extramarks. 

Before getting into the details, let’s glance through the list of topics included in this chapter:












Elements Of A Communication System

Basic Terminology Used In Electronic Communication Systems

Bandwidth Of Signals

Bandwidth Of Transmission Medium

Propagation Of Electromagnetic Waves

Modulation And Its Necessity

Amplitude Modulation

Production Of Amplitude Modulated Wave

Detection Of Amplitude Modulated Wave.

Students may click on the respective topic to access the study material for NCERT Solutions Class 12 Physics Chapter 15. Furthermore, here is a brief of the various topics covered under Chapter 15 Physics.

15.1 Introduction

Ch 15 Physics class 12 introduces the concepts of the mode of communication, modulation, and production and detection of Amplitude Modulated Wave. In this chapter, students will study how electromagnetic waves propagate through the earth’s atmosphere and the functioning of the Communication Systems. This section of NCERT Solutions Class 12 Physics Chapter 15 gives a brief introduction to the contribution of scientists like J.C. Bose, F.B. Morse, G. Marconi, and Alexander Graham Bell in the history of communication. 

15.2 Elements Of A Communication System

This section in the NCERT solutions class 12 Physics chapter 15 Communication systems gives brief information about the three essential elements- transistor, channel, and receiver. Students also learn about the two modes of communication. 

15.3 Basic Terminology Used In Electronic Communication Systems

It is vital that students know the basic terminologies under Physics to earn the complex topics and principles of communication chapters. Under this section in the Class 12 Physics chapter 15 NCERT solutions, students will learn about the signal, information source, noise, and transmitter. In addition, the concepts of Transducer, attenuation, amplification, range, bandwidth, modulation and communication satellite are explained in detail. 

15.4 Bandwidth of Signals

This section of NCERT solutions class 12 Physics Chapter 15 includes information on the Bandwidth of Signals. Its SI Unit is given as hertz (Hz). This section also helps students learn the difference between digital signals and analogue signals. A detailed stepwise explanation of how the rectangular waves are decomposed into a superposition of sinusoidal (sin) waves of frequencies. There is a figure mentioned which illustrates this fact. 

The NCERT solutions class 12 Physics Chapter 15 aim to help students perceive each concept better. 

15.5 Bandwidth Of Transmission Medium

Students will clearly understand the different bandwidths offered by transmission media. The table mentioned in the NCERT solutions class 12 Physics Chapter 15 displays the wireless communication frequency bands. Students will also gain knowledge about the two types of transmission media. They are as follows.

  1. Guided transmission medium: used in point to point and line communication. 
  2. Unguided transmission medium: used in space and satellite communication.

15.6 Propagation Of Electromagnetic Waves

The concept of propagation of em waves in the atmosphere of the earth is explained in detail. It includes a brief discussion about some useful layers in the earth’s atmosphere. This section is further divided into three parts in the NCERT Solutions Class 12 Physics Chapter 15. First, it gives information about the different modes of propagation, such as Ground wave, Sky wave, and Space wave. Students can easily understand these topics with the help of diagrams and tables. 

15.7 Modulation And Its Necessity

With the help of this section, students will know what modulation is and why it is necessary. Students also learn some factors such as the size of the antenna or aerial, the effective power radiated by an antenna, and the mixing up of signals from different transmitters, which prevents from transmitting an electronic signal, and how to overcome them. Graphical representation and detailed explanation are included in the class 12 Physics NCERT solutions chapter 15 of sinusoidal carrier wave dependent on the signal strength, amplitude, angular frequency, and the initial phase is mentioned in this section. 

15.8 Amplitude Modulation

This section is based on the previous topic. In this section, students will understand the process of amplitude modulation using the sinusoidal modulating signal. The derivations are explained in detail in a stepwise manner. NCERT Solutions Class 12 Physics Chapter 15 includes various numerical problems based on the formulas derived in this section. 

It is represented by  Cm(t)=Ac [1+AmAcsin mt]sin ct, where AmAc= is the amplitude modulation index. 

Furthermore, the production and detection of Amplitude Modulated Wave are explained in sections 15.9 and 15.10. Students will also know about the intermediate frequency (IF) stage in this section. 

Students may access the study material for the topics mentioned under NCERT Solutions Class 12 Physics Chapter 15 by clicking on the respective topic in the table.

List of NCERT Solutions Class 12 Physics Chapter 15 Exercise & Answer Solutions

The communication system is considered to be an easy and scoring chapter. To help students study better and enhance their learning process, Extramarks provides the NCERT Solutions Class 12 Physics Chapter 15. Students can practise lots of questions using the sample papers, CBSE question papers, and other important study resources. These notes provide apt and authentic information so that students can retain knowledge for a longer time. 

Click on the link provided below to get access to the NCERT Solutions Class 12 Physics Chapter 15:

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NCERT Exemplar Class 12 Physics

The NCERT Exemplar notes help students to gain in-depth knowledge of all chapters included in the CBSE Physics syllabus. Students can practise important CBSE questions framed by professionals and expert teachers. For example, chapter 15 NCERT solutions class 12 Physics provides detailed analysis so that students can understand the chapter clearly. The solutions are well-planned and explained in a detailed manner using coloured illustrations, graphs, and diagrams wherever necessary. Students can also learn various tips, tricks, and short-cut methods to tackle complex questions in an easy and quick way. 

Key Features of NCERT Solutions Class 12 Physics Chapter 15

The key features of the NCERT Solutions Class 12 Physics Chapter 15 provided by Extramarks include

  • A well-structured and organised set of solutions made by subject matter experts based on the analysis of the past years’  question papers.
  • The class 12 Physics NCERT solutions chapter 15 is based on the latest guidelines issued by the Central Board of Secondary education (CBSE). 
  • The notes include detailed and accurate solutions with precise reasoning to every question to ease the understanding of every student.  
  • The NCERT Solutions Class 12 Physics Chapter 15 enables quick revision as it provides all important formulae, equations, and derivations. 
  • It helps to develop and improve their problem-solving, logic, and analytical skills.

Q.1 What do you mean by remote sensing? Give its applications.
Ans. Remote Sensing: Remote sensing is a technique by which we can obtain information about a particular geographical area or object, from a distance without being in physical contact.
Applications of remote sensing: The applications of remote sensing are given as follows:-
1. By the help of remote sensing we can find out the information of cultivation of different crops in a particular area.
2. It is used in study and making of different kinds of maps also knowm as cartography.
3. It is used in oceanography i.e. for knowing the climatic condition, temperature and also to identify the potential fishing zones.
4. Remote sensing is useful in finding out the extent of pollution in any particular region and its sources too.
5. Remote sensing is used in predicting the temperature and weather and other climatic condition of a given area in advance.
6. It is also used during the period of natural calamities to assess the damage caused.
7. Remote sensing is used for spying in the field of defence and during war to locate the enemies.
8. It is used in the field of forestry. Remote sensing can give information about extent of forest cover, density of forest and types of plants. It is also helpful in detection and prevention of forest hazards like fire, excessive falling of of trees, etc.

Q.2 What is amplitude modulation? What is modulation index? Derive the expression for modulation index.
Ans. The variation of the amplitude of a carrier wave in accordance with the instantaneous value of the modulating(information) signal is called as amplitude modulation. The concept of generation of amplitude modulated signal is shown in the figure below,

Here the instantaneous value of the modulating signal is given by equation,

em=Emsinm t——(I) ;where, m is the angular frequency of the modulating signal.

Similarly the instantaneous value of the carrier signal is given by,

ec=Ecsinct——–(II) ;where, c is the angular frequency of the carrier signal.

Modulation Index: The ratio of amplitude of modulating signal to the amplitude of carrier is called as modulation index. It is also called as degree of modulation or depth of modulation. It is denoted by ma.

Here we have to find the expression for the ratio Em/Ec.

From fig(b), it follows that:-

Em= (Emax – Emin)/2 ———-(III)


Ec= Emax – E

Subsituting the value of Em from equation (III), we get:-

Ec= Emax – (Emax – Emin)/2

Ec= (Emax – Emin)/2 ————(IV)

Dividing equation (III) by (IV),

ma = Em/Ec = (Emax – Emin)/(Emax + Emin)

Q.3 Explain how communication is possible with the help of sky wave propagation?
Ans. In this type of communication the radiowaves transmitted and directed towards the sky are reflected back to earth at a distant location by the help of layer of atmosphere, also called as ionosphere.
The signal transmitted in this case must belong to the frequency range between 1710 kHz to 54 MHz. These waves are also called as short waves and are used for the transmission of radio signals. Ionosphere is the uppermost layer of the earth’s atmosphere and is located at the altitude of 65 km to 400 km. It contains ionized layers of electrons and ions, which are responsible for reflecting the transmitted signal back to earth. The signals which are above 54 Mhz escapes ionosphere and are not reflected back. Hence we can say that only a range of frequencies can be transmitted back towards earth.

Q.4 What are the processes involved in converting analog signal into digital signal? Explain pulse amplitude modulation (P.A.M).
Ans. The steps involved in converting analog signal into digital signal is shown below with the help of block schematic below,

Pulse Amplitude Modulation: In pulse amplitude modulation the pulses of the carrier pulse train is varied in accordance with the instantaneous value of the modulating signal.
Here from the figure below we can say that in pulse amplitude modulation the amplitude of pulses increseases or decreases in accordance with the modulating signal. In case of the pulse amplitude modulation the modulating signal is mixed with the modulating information signal to get the train of pulse amplitude signals. The pulse amplitude signal may be of single polarity or double polarity. If the train of pulses exists only in one direction than it is double polarity type P.A.M and if the pulses are present in both direction then it is called as double polarity P.A.M.

Q.5 What is satellite communication ? Explain its working.
Ans. The communication of signal between transmitter and receiver with the help of satellite is called as satellite communication.
Working: A satellite receives the signals from earth (which is beamed by transmitter), processes the signals and transmits them back to earth. The signal beamed by the satellite is received back on a distant location on earth, from which the original information signal is extracted by the process called demodulation.
The frequency at which satellite receive the signal is called as uplink frequency while the frequency at which satellite returns the signal towards earth is called as downlink frequency. The downlink frequency and uplink frequency are different so that there is no interference between these two signals.

Q.6 What are the merits and demerits of satellite communication?
Ans. The merits of satellite communication are given as follows:
1. It has a wide coverage area as compared to other communication systems.
2. Transmission of data at very high rate is possible through satellite communication.
3. Communication can be done from any part of earth just by using three geostationary satellites.
4. Communication done by the help of a satellite is much cheaper than other available means.
Demerits of satellite communication are given as follows:
1. The cost of launching satellite is very high and needs lot of technology expertise.
2. Every satellite has got its own time frame of working, after which it expires.
3. If there anything goes wrong in the satellite then there is no way we can fix the problem.
4. There is time delay between transmission and reception of signals, since they have to travel long distance(2×36,000=72,000 km).

Q.7 How would the following be affected in the absence of atmosphere around the earth?
a)Surface temperature of earth.
b)Range of radio waves transmission.
Give brief explanation in support of your.

Ans.a) The temperature of earth will decrease since the greenhouse effect will not take place in absence of atmosphere.
b) Range of radiowaves will decrease since reflecting layer(ionosphere) will be absent.

Q.8 A T.V tower has a height of 80m.What is its coverage area?
Ans. The coverage area is given by,

d= ( 2hR )1/2, where h=Height of the tower and R=radius of earth.

d= ( 2 x 80 x 6.4 x 106 )1/2 = 22627.5 m = 22.62 km.

Q.9 What is geostationary satellite ? What are its two characteristics?
Ans. Geostationary satellite: The satellite which appears to be at a fixed position to an observer on earth is called geostationary satellite.

The two characterstics of geostationary satellite are given as follows:

  1. It remains at a height of about 36,0000 km above the equator of earth.
  2. Its period of revolution should be equal to rotation of earth about its own axis i.e. 24 hours.

Q.10. Give two advantages of optical fibre communication?
Ans. The two advantages of optical fibre communication are given as follows:-
1. It can carry large amount of information signals at once.
2. It is able to carry even the high bandwidth carrier signals.

Q.11 What are the four primary constants of a transmission line?
Ans. The four primary constants of a transmission line are given as follows:-

  1. Resistance(R).
  2. Inductance(L).
  3. Capacitance(C).
  4. Conductance(G).

Q.12 Why is short wave band used for long distance radio broadcast?
Ans. Short waves have the frequency range of 2MHz to 20MHz. These waves can be reflected to earth by a layer of atmosphere called ionosphere. Hence we can use these waves for long distance radio transmission.

Q.13 Find the length of the dipole antenna for a carrier wave of wavelength ?
Ans. The length of the dipole antenna will be equal to / 2.

Q.14 What should be the length of a dipole antenna for a carrier wave having frequency 3×108 Hz?
Ans. Length of dipole antenna = / 2—–I.

We are given with the frequency of carrier wave, evaluate wavelength from it by relation,

= c / f = ( 3 x 108 ) / ( 6 x 108 ) = 0.5 m.

Substituting the above value in equation I we get,

Lemgth of dipole antenna=(0.5 / 2) = 0.25 m.

Q.15 What do you mean by bandwidth?
Ans. The total spread of a signal over a range of frequencies is called its bandwidth.

Q.16 How does the power radiated by an antenna vary with wavelength?
Ans. The power radiated by an antenna is related to wavelength by relation,

P ( 1 / 2).

Q.17 Name the type of modulation scheme preferred for digital communication.
Ans. For digital communication we prefer pulse code modulation (P.C.M).

Q.18 What is sampling frequency?
Ans. The number of samples taken per second for a given analog signal is called its sampling frequency.

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FAQs (Frequently Asked Questions)

1. Which essential concepts are covered in NCERT Solutions Class 12 Physics Chapter 15?

The NCERT Solutions cover solutions to all questions based on topics like Bandwidth of signals, Propagation of Electromagnetic waves, Modulation, Demodulation, and Effective power radiated by an antenna. Extramarks notes have tried to explain all these topics from the roots to enable in-depth understanding.

2. Which reference books should I use to study CBSE Class 12 Physics?

 Reference books are essential as they help in effective preparation for CBSE exams as well as competitive exams such as JEE and NEET. There are various books published by NCERT that students should study thoroughly.

Here is the list of some of the best reference books: 

  • Concepts of Physics by H C Verma
  • Objective Physics by DC Pandey
  • Fundamentals of Physics by Halliday, Resnick & Walker
  • CBSE Chapter-wise Solutions – Physics by S. K. Singh
  • New Simplified Physics by Dhanpat Rai (Set of 2 Volumes)