NCERT Class 12 Physics Solutions Communication Systems

NCERT Class 12 Physics Solutions Communication Systems- NCERT Solutions prepared for CBSE students by the best teachers in Delhi.

Class XII Chapter 15 – Communication Systems Physics

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

Answer :(b) Answer: 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.

Answer (d) Answer: 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).

Answer (c) Answer: 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?

 Answer:Line-of-sight communication means that there is no physical obstruction between thetransmitter 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, d = 2Rh, 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

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%?

Question 15.7: For an amplitude modulated wave, the maximum amplitude is found to be 10 V while theminimum 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?

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.


Students should free download the NCERT solutions and get better marks in exams. Studiestoday.com panel of teachers recommend students to practice questions in NCERT books and download NCERT solutions.

Tags: 

 


Click to View or Download pdf file
Click for more Physics Study Material

Latest NCERT & CBSE News

Read the latest news and announcements from NCERT and CBSE below. Important updates relating to your studies which will help you to keep yourself updated with latest happenings in school level education. Keep yourself updated with all latest news and also read articles from teachers which will help you to improve your studies, increase motivation level and promote faster learning

Training of CBSE School Teachers on Olabs

Training of CBSE School Teachers on Olabs in collaboration with C-DAC Mumbai: OLabs is a platform jointly developed by the Ministry of Electronics and Telecommunications, Government of India, CDAC, and Amrita University to facilitate a virtual experience of CBSE...

Conduct of the practical work during the lockdown

CBSE has advised schools to follow the Alternative Calendar developed by NCERT to continue education during the lockdown through alternative modes to achieve learning outcomes. Schools have reportedly started using these calendars and other prescribed pedagogical...

TERI Green Olympiad 2020

Green Olympiad is a value driven project conducted by TERI (The Energy and Resources Institute) for school students annually since 1999. This Olympiad assesses the environment quotient of students and also enhances their understanding on issues related to sustainable...

National Online Painting Championship

The National Mission for Clean Ganga, Ministry of Jal Shakti in collaboration with Kalantar Art Trust is organizing KALANTAR-2020: National Online Painting Championship with the aim to provide a platform to youth and school children to demonstrate their artistic skills...

Keep your kids engaged during Lockdown

Kids are the Future of our Country! Outlines have changed and so should the formats of existence! It is the best time to teach our kids the pleasure of Self-Discipline, Self-Realization and Self-Control. To keep the future generation safe in such unpredictable...

Online Teacher Training Course on Competency based Education in DIKSHA

Competency is a set of skills, abilities, knowledge that helps an individual perform a given task in real life. Every learning should go into the imbibing of these skills to lead a productive and joyful life. The NATIONAL EDUCATION POLICY-2020 calls for shift towards...

×
Studies Today