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# NCERT Solution for Class 12 Physics Chapter 15

Get Free NCERT Solutions for Class 12 Physics Chapter 15 Communication Systems, set up after careful examination by profoundly experienced Physics instructors, at Swastik Classes. NCERT Solutions are extremely helpful while doing your homework and also for your Class 12 board exam preparation. We have given bit-by-bit answers to every one of the questions given in the NCERT class 12 Physics course reading. This solution is free to download and the questions are systematically arranged for your ease of preparation and in solving different types of questions. To score good marks, students are encouraged to get familiar with these NCERT solutions of Chapter 15 Communication Systems.

## Answers of Physics NCERT solutions for class 12 Chapter 15 – Communication Systems

Question 15.1:

Which of the following frequencies will be suitable for beyond-the-horizon communication using sky waves?

(a) 10 kHz

(b)  10 MHz

(c)  1 GHz

(d)  1000 GHz

(b)

10 MHz

For beyond-the-horizon communication, it is necessary for the signal waves to travel a large distance. 10 KHz signals cannot be radiated efficiently because of the antenna size. The high energy signal waves (1GHz − 1000 GHz) penetrate the ionosphere. 10 MHz frequencies get reflected easily from the ionosphere. Hence, signal waves of such frequencies are suitable for beyond-the-horizon communication.

Question 15.2:

Frequencies in the UHF range normally propagate by means of:

(a)  Ground waves.

(b)  Sky waves.

(c)  Surface waves.

(d)  Space waves.

(d)

Space waves

Owing to its high frequency, an ultra high frequency (UHF) wave can neither travel along the trajectory of the ground nor can it get reflected by the ionosphere. The signals having UHF are propagated through line-of-sight communication, which is nothing but space wave propagation.

Question 15.3:

Digital signals

(i) Do not provide a continuous set of values,

(ii) Represent values as discrete steps,

(iii) Can utilize binary system, and

(iv) Can utilize decimal as well as binary systems.

Which of the above statements are true?

(a) (i) and (ii) only

(b) (ii) and (iii) only

(c) (i), (ii) and (iii) but not (iv)

(d) All of (i), (ii), (iii) and (iv).

A digital signal uses the binary (0 and 1) system for transferring message signals. Such a system cannot utilise the decimal system (which corresponds to analogue signals). Digital signals represent discontinuous values.

Question 15.4:

Is it necessary for a transmitting antenna to be at the same height as that of the receiving antenna for line-of-sight communication? A TV transmitting antenna is 81m tall. How much service area can it cover if the receiving antenna is at the ground level?

Line-of-sight communication means that there is no physical obstruction between the transmitter and the receiver. In such communications it is not necessary for the transmitting and receiving antennas to be at the same height.

Height of the given antenna, h = 81 m

Radius of earth, R = 6.4 × 106 m

For range, = (2Rh)½, the service area of the antenna is given by the relation:

A = πd2

= π (2Rh)

= 3.14 × 2 × 6.4 × 106 × 81

= 3255.55 × 106 m2

= 3255.55

∼ 3256 km2

Question 15.5:

A carrier wave of peak voltage 12 V is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of 75%?

Amplitude of the carrier wave, Ac = 12 V

Modulation index, m = 75% = 0.75

Amplitude of the modulating wave = Am

Using the relation for modulation index:

Question 15.6:

A modulating signal is a square wave, as shown in Fig. 15.14.

The carrier wave is given by

(i)  Sketch the amplitude modulated waveform

(ii)  What is the modulation index?

It can be observed from the given modulating signal that the amplitude of the modulating signal, Am = 1 V

It is given that the carrier wave c (t) = 2 sin (8πt)

∴Amplitude of the carrier wave, Ac = 2 V

Time period of the modulating signal Tm = 1 s

The angular frequency of the modulating signal is calculated as:

The angular frequency of the carrier signal is calculated as:

From equations (i) and (ii), we get:

The amplitude modulated waveform of the modulating signal is shown in the following figure.

(ii) Modulation index,

Question 15.7:

For an amplitude modulated wave, the maximum amplitude is found to be 10 V while the minimum amplitude is found to be 2 V. Determine the modulation index μ. What would be the value of μ if the minimum amplitude is zero volt?

Maximum amplitude, Amax = 10 V

Minimum amplitude, Amin = 2 V

Modulation index μ, is given by the relation:

Question 15.8:

Due to economic reasons, only the upper sideband of an AM wave is transmitted, but at the receiving station, there is a facility for generating the carrier. Show that if a device is available which can multiply two signals, then it is possible to recover the modulating signal at the receiver station.

Let ωc and ωs be the respective frequencies of the carrier and signal waves.

Signal received at the receiving station, V = V1 cos (ωc + ωs)t

Instantaneous voltage of the carrier wave, Vin = Vc cos ωct

At the receiving station, the low-pass filter allows only high frequency signals to pass through it. It obstructs the low frequency signal ωs. Thus, at the receiving station, one can record the modulating signal which is the signal frequency.

Communication systems are simply a collection of systems used for transmission, connection, communication and interconnection. These systems are categorically arranged into three different types on the basis of uses such as the Media, Technology and Application area. Sensors, Transducers, Emitters and Amplifiers are all examples of modern technology that are used as components in the majority of modern devices.

### Topics to study in Physics Class 12 Chapter 15 Communication Systems

 Section no. Topics 14.1 Introduction 14.2 Classifications of Metals, Conductors and Semiconductors 14.3 Intrinsic Semiconductor 14.4 Extrinsic Semiconductor 14.5 P-n Junction 14.6 Semiconductor Diode 14.7 Application of Junction Diode as a Rectifier 14.8 Special Purpose p-n Junction Diodes 14.9 Digital Electronics and Logic Gates

## Frequently Asked Questions on NCERT Solutions for Class 12 Physics Chapter 15

### What are the types of questions asked from Chapter 15 of NCERT Solutions for Class 12 Physics?

The types of questions asked from Chapter 15 of NCERT Solutions for Class 12 Physics are –
1. Very short answers
Students can answer the very short answer type of questions in a single sentence.

### Can I download the PDF of NCERT Solutions for Class 12 Physics Chapter 15 for free?

Yes, you can download the PDF of NCERT Solutions for Class 12 Physics Chapter 15 for free from SWC. The solutions are designed based on the latest CBSE syllabus and guidelines. The chapter wise and exercise wise PDF links are provided to help students boost their exam preparation. All the answers are strictly based on the textbook prescribed by the CBSE board. The solutions PDF help students to improve their logical reasoning and analytical thinking skills, which are extremely important for the exam.

### What is the concept of amplitude modulation discussed in the Chapter 15 of NCERT Solutions for Class 12 Physics?

Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. It is often called AM and is commonly used in transmitting a piece of information through a radio carrier wave. Amplitude modulation is mostly used in the form of electronic communication. This concept is explained with various examples in order to provide in-depth knowledge among students. The solutions of Chapter 15 are designed by the faculty at SWC keeping in mind the understanding abilities of students. To get a clear idea about the concepts covered in this chapter, students are advised to download the solutions PDF available in SWC

# NCERT Solutions Class 12 Maths Chapters

• Chapter 1 Electric Charges and Fields
• Chapter 2 Electrostatic Potential and Capacitance
• Chapter 3 Current Electricity
• Chapter 4 Moving Charges and Magnetism
• Chapter 5 Magnetism and Matter
• Chapter 6 Electromagnetic Induction
• Chapter 7 Alternating Current
• Chapter 8 Electromagnetic Waves
• Chapter 9 Ray Optics and Optical Instruments
• Chapter 10 Wave Optics
• Chapter 11 Dual Nature of Radiation and Matter
• Chapter 12 Atoms
• Chapter 13 Nuclei
• Chapter 14 Semiconductor Electronics
• Chapter 15 Communication Systems