CBSE Class 12 Physics Revision Notes Chapter 15

Class 12 Physics Chapter 15 notes

*According to the latest CBSE Syllabus 2021-22, this chapter is not included.*

Physics is considered to be one of the most challenging and demanding subjects. It requires a special approach to the mathematics and theory involved. A basic understanding of physics will make other sciences easy. 

Students should consider referring to the Class 12 Physics Chapter 15 notes to gain in-depth knowledge about all the concepts. These revision notes eliminate the habit of rote learning and help the students to understand the formulae, derivations and topics. Extramarks provides the chapter 15 physics Class 12 notes to make the complicated problems easy and to increase their understanding. 

Extramarks provides a holistic learning experience through its detailed study materials to help students excel in their academics.

Key Topics Covered In Class 12 Physics Chapter 15 Notes

The key topics covered under Class 12 Physics Chapter 15 notes include the following.

INTRODUCTION

Communication is defined as the act of sending and receiving information. For successful communication, the sender and the receiver must understand a common language. Languages and different communication methods have been evolving since prehistoric times to satisfy the growing demands of information in terms of speed and complexity.

Chapter 15 physics Class 12 notes explain the work of J.C. Bose, F.B. Morse, G. Marconi and Alexander Graham Bell. It aims to introduce different communication concepts, such as the mode of communication, the need for modulation, and the production and deduction of amplitude modulation.

ELEMENTS OF A COMMUNICATION SYSTEM

Every communication system has three essential elements. They are the transmitter, medium and receiver. The block diagram below depicts a general form of the communication system.

In a communication system, the transmitter is kept at one place, the receiver is kept at another place away from the transmitter, and the channel connects them. A channel may be like wires or cables or wireless, depending on the type of the communication system. It converts the message signal produced by the source to another form that can be transmitted through the channel. If the output of the source is a non-electrical signal, then a transducer is used to convert it to an electrical form before it gives it an input to the transmitter. 

When transmission of the signal takes place along a channel, there are chances that it may get distorted because of channel imperfection. 

The receiver of the communication system operates on the received signal and reconstructs it to a recognisable form of the original message to deliver it to the user. 

There are two different types of communication:

• Point-to-point communication: In this case, communication occurs between a single transmitter and receiver. For example, telephony. 
• Broadcast mode: In this case, communication takes place between a single transmitter and a large number of receivers. For example, Radio. 

The Class 12 Physics Chapter 15 notes explain the elements of communication system in detail. 

BASIC TERMINOLOGY

(i) Transducer: The device that is used to convert one form of energy into another is called a transducer. Some devices have either their inputs or outputs in the electrical form in communication systems. A transducer is also termed as a device that converts a physical variable into its corresponding variations in the electrical signal at the output. 

(ii) Signal: The information that is converted into electrical form and can be transmitted is called a signal. They can be analogue or digital. Analogue signals are known to be continuous variations of voltage (V) or current (I). They are single-valued functions with respect to time. Sound and picture signals in Television are analogue. The digital signals can take only discrete stepwise values. The binary system extensively uses two levels of a signal. ‘0’ for low level and ‘1’ for a high voltage or current level. 

(iii) Noise: Noise is the unwanted signal that disturbs the system’s transmission and processing of message signals. The source which generates the noise is located inside or outside the communication system. 

(iv) Transmitter: A transmitter is a device which processes the incoming message signal to transmit through the channel and subsequent reception. 

(v) Receiver: A receiver is a device which extracts the message signals from received signals at the output. 

(vi) Attenuation: Attenuation is known as the loss of strength of a signal when it propagates through a medium.

(vii) Amplification: It is the process where the amplitude of a signal is increased with the help of an electronic circuit called the amplifier. This process is necessary to compensate for the loss of strength of a signal in the communication systems. 

(viii) Range: The largest distance between a source and the destination where the signal is received with particular strength is the range of the signal. 

(ix) Bandwidth: Bandwidth is the frequency range where the equipment operates. It is also said to be the portion of the spectrum inhabited by the signal. 

(x) Modulation: The original low-frequency signal cannot be transmitted to long distances. Therefore, at the transmitter, the information contained in the signal is superimposed on a high-frequency wave. This acts as the carrier of information. This process is called modulation. 

(xi) Demodulation: When the information is retrieved from the carrier wave at the receiver is known as demodulation. 

(xii) Repeater: A repeater is termed as a combination of a receiver and a transmitter. This system picks up the signal/message from the transmitter. It then amplifies and retransmits it to the receiver with a change in carrier frequency. 

Class 12 Physics Chapter 15 notes provide well-explained information about these terms. 

BANDWIDTH OF SIGNALS

In a continuous belt of frequencies, the bandwidth is said to be the difference between the upper and lower frequencies. It is generally measured in hertz (Hz). 

The message signal can either be voice, music, picture or even computer data. In a communication system, these signals have different ranges of frequencies from 300 Hz to 3100 Hz. The types of communication systems needed depend on the range of frequencies essential for the process of communication. 

BANDWIDTH OF TRANSMISSION MEDIUM

The different types of transmission media have different bandwidths. Wire, free space, coaxial cable and fibre optic cable are the commonly used transmission media. The table mentioned below are the  details about the range of frequencies allotted to various services. 

Transmission media are divided into two different types: 

• Guided transmission medium: It is termed to be a communication medium which is used between a single transmitter and a receiver in point to point communication. It is used in line communication. 
• Unguided transmission medium: It is defined as a communication medium which is used between the transmitter and receiver, in no point to point contact. An example of an unguided transmission medium is free space. 

PROPAGATION OF ELECTROMAGNETIC WAVES

An antenna radiates the electromagnetic waves at the transmitter in communication using radio waves. These waves travel through space and reach the receiving antenna places at a distance. The factors which affect the propagation of Electromagnetic waves are given below:

(i) Ground Wave: The antennas must have a size comparable to the wavelength A of the signal so that signals can be radiated with high efficiency. The antennas have a significant physical size at longer wavelengths and shorter frequencies. They are located very near the ground. Ground-based vertical towers are used as transmitting antennas. For such antennas, the ground influences the propagation of the signal strength. Therefore, the mode of propagation is known as surface wave propagation. 

As the wave passes, it induces a current in the ground and is attenuated as the earth absorbs the energy. The attenuation of ground waves increases rapidly as the frequency of the wave increases. 

(ii) Skywaves: With the help of the ionospheric reflection of radio waves, long-distance communication is achieved. Skywaves are used by short wave broadcast services. The ionosphere means the presence of a large number of charged particles (ions). 

It ranges from 65 km to 400 km, approximately above the surface of the earth. It takes place due to the absorption of the high-energy radiation coming from the sun. As density of the atmosphere decreases with an increase in height. At great heights, there are few molecules to be ionised. However, closer to the earth, the molecular concentration is very high, and so the radiation intensity is low. 

At some intermediate heights, it is observed that the ionisation density is maximum. This layer acts as a reflector for a range of 3 to 30 MHz frequencies. The EM waves having higher than 30 MHz frequency will penetrate the ionosphere and escape.

(iii) Space wave: A space wave travels straight to the receiving antenna from the transmitting antenna. These waves are used for line-of-sight and satellite communication. At frequencies higher than 40 MHz, communication is limited to LOS paths. The antennas are relatively more minor at these frequencies and can be placed at heights above the ground. 

Because of the line-of-sight communication, the direct waves are blocked by the earth’s curvature. To receive the signal beyond the horizon, the receiving antenna must be placed high to intercept the line-of-sight waves. 

Understand the propagation of EM waves thoroughly with the help of the CBSE Class 12 physics chapter 15 notes. 

MODULATION AND ITS NECESSITY

Modulation is the phenomenon where the low audio frequency information (modulating signals) is superimposed on a high-frequency carrier wave. The resultant waves thus obtained are termed the modulated wave, which is transmitted.

The various types of modulation are:

• Amplitude modulation (AM)
• Frequency modulation (FM)
• Phase modulation (PM)

Size of the antenna or aerial:

An antenna is required for transmitting a signal. The size of this antenna should be comparable to the wavelength of the signal as the antenna senses the time variation of the signal. Direct transmission of an electromagnetic wave of 20 kHz is not practical as its wavelength λ is 15 km. Therefore, this transmission is obtained with the help of reasonable antenna lengths. For this, the original low-frequency baseband signal should be translated into high frequencies before transmission.

Effective power radiated by an antenna 

The power of a linear antenna of length (l) is proportional to (l)2. This means that for the length of the antenna, the power radiated increases as wavelength λ decreases, i.e., increasing frequency. Hence, the effective power would be smaller if radiated by a long-wavelength signal. For a good transmission, high powers are required, which implies we need a high-frequency transmission. 

Mixing up signals from different transmitters 

Suppose many transmitters are transmitting information signals at the same time. All these signals will be mixed, and there will be no way to distinguish between them. This can be done by using communication at high frequencies and allotting them to each signal for its transmission. 

The translated signal will possess the information which was contained in the original signal. For translation, consider a high-frequency signal, also known as the carrier wave. This process is known as modulation. 

The carrier wave is a continuous sinusoidal wave or is in the form of pulses. This wave is represented as

c(t) = Ac sin(ct+), where c(t) is signal strength, Ac is the amplitude, c= 2πc is the angular frequency, and φ is the initial phase. The parameters Ac, c and φ, can be controlled by the message during modulation.

The various types of pulse modulation are:

• Pulse Position Modulation (PPM)
• Pulse Width Modulation (PWM)
• Pulse Duration Modulation (PDM)
• Pulse Amplitude Modulation (PAM)

AMPLITUDE MODULATION

In this process, the amplitude of the carrier wave is varied in accordance with the information signal.

Let c(t) = Ac sin(ct+) be the carrier wave and m(t) = Am sin(mt+), where m= 2πfm be the modulating signal. 

The amplitude modulation is cm(t)= (Ac+Amsin mt)sin ct

Therefore, cm(t)= Ac [ 1 + AmAc sin mt] sin ct, where AmAc = is the amplitude modulation signal.

Several important questions and problems based on this section are included in the notes of Class 12 physics chapter 15. 

INTERNET

It is a system which has billions of users worldwide. It allows communication and sharing of information between two or more computers connected through a complex network. It was started and opened for public use in the late 90s. With time, there was tremendous growth, and it is still expanding. Following are the applications: 

(i) Email – It allows theexchange of text/graphic material using the email software. We can write letters and send them to the recipient through ISPs who dispatch and receive the messages.

(ii) File transfer – An FTP allows the transfer of files/software between two computers connected with each other via the Internet. 

(iii) World Wide Web (WWW) – The computers store specific information which can be shared with others through websites and web service providers. Any individual can post information about their activities on their websites. This information will be accessible to the other users. Search engines like Google help us to find information by listing related websites. 

(iv) E-commerce – Using the internet to promote a business using electronic means is called E-commerce. Customers can view images and receive all the information about the different products or services through their websites. Individuals can do online shopping from their homes/offices. 

(v) Chat – Chat is defined as a real-time conversation which takes place among people through typed messages. Everyone who belongs to the chat group can see the message instantaneously and respond rapidly. 

Facsimile (FAX):

It is used to scan the contents of a document to produce electronic signals. These signals are sent to the destination in an orderly manner with the help of telephone lines. At the destination (FAX machine), the signals are converted again into a replica of the original message.

Mobile telephony 

This concept was developed first in the 1970s and was implemented in the next decade. The basic concept of this system is to divide the service areas into several numbers of cells centred on an office called MTSO. 

Each cell contains a low-power transmitter, known as the base station and helps a large number of mobile receivers. Each cellphone could have a service area of limited square kilometres, depending on the number of customers. When a mobile receiver crosses the coverage area of one base station, it must be transferred to another base station. This procedure is termed to be handover or handoff. It is carried out very rapidly so that the consumer does not even notice it. Mobile telephones typically operate in about 800-950 MHz range of frequencies.

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Class 12 Physics Chapter 15 notes: Exercises &  Solutions

The Extramarks platform provides the best study material for students to attain high scores and pursue their dream careers. The Class 12 physics chapter 15 notes include solutions to all exercise problems, solved examples and some CBSE extra questions as well. It is curated by the subject matter experts at Extramarks after analysing several CBSE past year question papers. The Class 12 physics chapter 15 notes help students in their preparation not only for the board exams but also for various national level competitive examinations such as NEET, JEE, etc. With the help of these notes, students can get a clear idea of the type of questions that will be asked in the exams. 

Using the Class 12 physics chapter 15 notes, students can analyse themselves based on their preparation level and also plan their studies to cover the entire CBSE syllabus. The exercise and solutions provided by Extramarks act like a guide, which students can refer to in case they face any difficulties. 

To get an overview, key concepts and quick revision of the entire chapter, refer to the link mentioned below

Key Features of Class 12 Physics Chapter 15 notes

The key features of Extramarks Class 12 Physics Chapter 15 notes are as follows:

• Class 12 Physics Chapter 15 notes are prepared extensively by the elites of Extramarks through detailed research. 
• The CBSE revision notes are crucial to prepare appropriately for exams.
• It helps students to review key points, recall necessary details and solidify their knowledge of all concepts.
• They are concise, well-organised and provide apt knowledge. 
• They follow the latest guidelines of the CBSE (Central Board of Secondary education) board.
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