NCERT Class 12 Physics Solutions Communication Systems

Scroll down for PDF

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 on the text For more study material for Physics please click here - Physics

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

CBSE schools to have sports period daily for classes 1 to 12

CBSE schools to have sports period daily for classes 1 to 12, new curriculum introduced All work and no play makes a child dull. Nowadays students have a very hectic schedule so that they cannot take out time to play games and gently start ignoring sports. Therefore,...

Do you think getting a tutor to help your child is a good idea

Yes, getting a tutor is a good idea to help your child. There are many reasons why parents choose tutors for their children. Some parents feel unable to help their children with homework and some don’t have enough time for this. Some think that their children are more...

Sample Papers for Class 12 Boards 2020

CBSE has released the final sample papers for the class 12 boards exams as per the new pattern as per which the question papers are expected to come in the 2020 board exams for class 12. The sample papers have been for class 12 for all subjects along with the suggested...

CBSE Instructs schools to form Eco Clubs

The Central Board of Secondary Education has directed schools to form Eco Clubs under the Board for Environmental Protection. They have further asked the schools to ensure that every student would save one litre of water at home and school every day. It was started by...

CBSE class 10, 12 board exam important information

CBSE class 10, 12 board exam: important information to prevent problems for students : The Central Board of Secondary Education (CBSE) has issued an advisory for the students of class 10 and class 12 board. As per the notice, the registration of students appearing in...

CBSE Class 10 Board Exam 2020

CBSE Class 10 Board Exam 2020: Problems Students May Face In Choosing Subject The Central Board of Secondary Education (CBSE) class 10 board examination will start from February 2020. The Central Board of Secondary Education (CBSE) has started the process of filling...

×
Studies Today