NCERT Exemplar Class 12 Physics Solutions Chapter 15 Communication System
NCERT Exemplar Class 12 Physics solutions chapter 15 introduces the wonder of transmission of information, also called communication. As humans, we process millions of information fragments every second by receiving them through a multitude of sources- that is where communication comes in, to make sure the efficient transfer and delivery of information. How is efficient communication possible? How can one share his thoughts or ideas? NCERT Exemplar Class 12 Physics chapter 15 solutions given on this page would help you articulate your ideas properly and adequately communicate them, be it in your academics orally. They would also aid in giving a good performance in the 12 boards and other competitive exams. NCERT Exemplar Class 12 Physics solutions chapter 15 PDF download can also be brought into use by the students.
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NCERT Exemplar Class 12 Physics Solutions Chapter 15 MCQI
Three waves A, B and C of frequencies 1600 kHz, 5 MHz and 60 MHz respectively are to be transmitted from one place to another. Which of the following is the most appropriate mode of communication?
(a) A is transmitted via space wave while B and C are transmitted via sky wave
(b) A is transmitted via ground wave, B via sky wave and C via space wave
(c) B and C are transmitted via ground wave while A is transmitted via sky wave
(d) B is transmitted via ground wave while A and C are transmitted via space wave
Answer:The correct option is (b) A is transmitted via ground wave, B via skywave and C via space wave. Because the ground wave propagation is only suitable for up to 2MHz frequencies, and the space wave propagation is for the frequencies more than 40 MHz, whereas the skywave propagation is used for frequencies ranging from 30 to 40 MHz.
100m long antenna is mounted on a 500m tall building. The complex can become a transmission tower for waves with λ
(a) ~ 400 m
(b) ~ 25 m
(c) ~ 150 m
(d) ~ 2400 m
Answer:It can easily be calculated as
Length of the building
Length of the antenna
And thus the wavelength of the wave transmitted would be
A1 kW signal is transmitted using a communication channel which provides attenuation at the rate of -2dB per km. If the communication channel has a total length of 5 km, the power of the signal received is [gain in dB =10 log(p0/pi)]
(a) 900 W (b) 100 W (c) 990 W (d) 1010 W
To calculate the power of the signal transmitted,
The rate of attenuation of the signal
The given total length of the path
The formula used
After putting all he values,
A speech signal of 3 kHz is used to modulate a carrier signal of frequency 1 MHz, using amplitude modulation. The frequencies of the side bands will be
(a) 1.003 MHz and 0.997 MHz
(b) 3001 kHz and 2997 kHz
(c) 1003 kHz and 1000 kHz
(d) 1 MHz and 0.997 MHz
The frequencies of the sidebands would be (a) 1.003 MHz and 0.997 MHz
A message signal of frequency is superposed on a carrier wave of frequency to get an amplitude modulated wave (AM). The frequency of the AM wave will be
Answer:Since the frequencies of both the carrier wave and the amplitude-modulated wave are similar, the frequency of the AM wave would be (b) ωc
I-V characteristics of four devices are shown in the figure.
Identify devices that can be used for modulation:
(a) ‘i’ and ‘iii’
(b) only ‘iii’
(c) ‘ii’ and some regions of ‘iv’
(d) All the devices can be used.
From the above-given figures, option ii) represents the square-law diode modulation and the option iv) represents some of its parts as the square law modulation there for the correct option is (c) ‘ii’ and some regions of ‘iv’
A male voice after modulation-transmission sounds like that of a female to the receiver. The problem is due to
(a) poor selection of modulation index (selected 0 < m < 1)
(b) poor bandwidth selection of amplifiers
(c) poor selection of carrier frequency
(d) loss of energy in transmission
Answer:When the selection of bandwidth for transmission is improper, the frequency of the modulated signal becomes more though the male voice frequency is less than female; thus, the voice sounds feminine. Therefore, the answer is (b) poor bandwidth selection of amplifiers
A basic communication system consists of
(B) information source
(C) user of information
Choose the correct sequence in which these are arranged in a basic communication system:
Answer:As clearly stated by the order explained in the given below chain –
Information source Transmitter Channel Receiver user of information
The correct order is option (b) BADEC
Identify the mathematical expression for amplitude modulated wave:
The correct mathematical expression for amplitude modulated wave is
NCERT Exemplar Class 12 Physics Solutions Chapter 15 MCQII
An audio signal of 15 kHz frequency cannot be transmitted over long distances without modulation, because
(a) the size of the required antenna would be at least 5 km which is not convenient
(b) the audio signal cannot be transmitted through sky waves
(c) the size of the required antenna would be at least 20 km, which is not convenient
(d) effective power transmitted would be very low, if the size of the antenna is less than 5 km
Answer:The correct answer is the options (a, b, d)
The audio frequency signals transmitted are of extremely low-frequency waves, and due to the absorption of sky waves by the atmosphere, they cannot transmit the radio waves. And the size of the antenna used must not be less than 5 km as it would degrade the quality of transmission significantly. This would be due to the resonance of wavelength of wave and antenna length. So, the correct options are (a), (b), and (d).
Audio sine waves of 3 kHz frequency are used to amplitude modulate a carrier signal of 1.5 MHz Which of the following statements are true?
(a) The sideband frequencies are 1506 kHz and 1494 kHz
(b) The bandwidth required for amplitude modulation is 6kHz
(c) The bandwidth required for amplitude modulation is 3 MHz
(d) The sideband frequencies are 1503 kHz and 1497 kHz.
Answer:The types of frequencies under the AM wave are of three types, and the sideband frequencies in AM waves are close to the carrier waves. So according to the given criteria,
The bandwidth required for amplitude modulation is 6kHz and The sideband frequencies are 1503 kHz and 1497 kHz
So, the correct options are (b) and (d)
A TV transmission tower has a height of 240 m. Signals broadcast from this tower will be received by LOS communication at a distance of (assume the radius of the earth to be 6.4 × 106 m)
(a) 100 km
(b) 24 km
(c) 55 km
(d) 50 km
Answer:To calculate the maximum signal transmission from any TV towers, the formula is –
So, the distances up to which the signal can be received are (b) 24 km, (c) 55 km, (d) 50 km
The frequency response curve in the figure for the filter circuit used for production of AM wave should be
(a) (i) followed by(ii)
(b) (ii) followed by (i)
The bandwidth for the production of amplitude modulated wave is given by the relation =
à Frequency of upper band – frequency of a lower band
Therefore, the correct options are (a) (i) followed by(ii), (b) (ii) followed by (i), (c) (iii)
In amplitude modulation, the modulation index m is kept less than or equal to 1 because
(a) m > 1, will result in interference between the carrier frequency and message frequency, resulting in distortion
(b) m > 1 will result in overlapping of both sidebands resulting in loss of information
(c) m > 1 will result in a change in phase between the carrier signal and the message signal
(d) m > 1 indicates the amplitude of message signal greater than the amplitude of the carrier signal resulting in distortion
Answer:Due to the occurrence of overmodulation , this leads to higher chances of sideband overlapping and fading (loss of information). If the value of u is approximately equal to 1, it results in a distortion f carrier wave.
Thus option (b) and (d) are the right answers.
Which of the following would produce analogue signals and which would produce digital signals?
(i) A vibrating tuning forks
(ii) Musical sound due to a vibrating sitar string
(iii) Light pulse
(iv) Output of NAND gate
Answer:Analogue signals will be produced by option i) and ii), i.e. a vibrating tuning fork and musical sound due to a vibrating sitar string.
Whereas option iii) and iv) will produce digital signals which are light pulse and output of NAND gate.
NCERT Exemplar Class 12 Physics Solutions Chapter 15 Very Short Answer
Would sky waves be suitable for transmission of TV signals of 60 MHz frequency?
Answer:As the frequency of TV signals is beyond 60 MHz, the skywaves are not reliable for transmission of 60 MHz frequency TV signals. The waves preferred for this type of transmission are space waves.
Two waves A and B of frequencies 2 MHz and 3 MHz respectively are beamed in the same direction for communication via sky wave. Which one of these is likely to travel a longer distance in the ionosphere before suffering total internal reflection?
Answer:Frequency and refractive index are directly proportional; thus, due to wave B having a higher frequency than wave A, the refractive index of wave B is higher than the refractive index of wave A.
The maximum amplitude of an A.M. wave is found to be 15 V while its minimum amplitude is found to be 3 V. What is the modulation index?
Answer:The change in the ratio of the amplitude of the carrier wave to the amplitude of the original carrier wave is defined as the modulation index.
The given maximum amplitude of the AM wave is
The given minimum amplitude of the AM wave is
Thus, the modulation index, m, would be
Compute the LC product of a tuned amplifier circuit required to generate a carrier wave of 1 MHz for amplitude modulation.
Answer:The formula for the frequency of the tuned amplifier is,
As given in the question
After substituting the values, the answer would be
Why is an AM signal likely to be noisier than an FM signal upon transmission through a channel?
Answer:AM signal has the characteristic feature of being noisy when broadcasted on channels as compared to the FM signal because its carrier waves’ instantaneous voltage varies by the modulating wave voltage in the AM.
NCERT Exemplar Class 12 Physics Solutions Chapter 15 Short Answer
Figure shows a communication system. What is the output power when the input signal is of 1.01mW? (gain in dB = 10 log10 (Po /Pi ).
The loss of signal during the transmission
The total path covered by the signal
Collective loss suffered
Total amplifier gain
Total gain in signal
Gain in dB
Thus, output power would be,
A TV transmission tower antenna is at the height of 20 m. How much service area can it cover if the receiving antenna is (i) at ground level, (ii) at the height of 25 m? Calculate the percentage increase in area covered in case (ii) relative to the case (i).
Answer:As given in the question,
For the first part
i) Range of the signals, it = 16 km
Area covered by the waves = 803.84 km2
ii) Height of antenna from ground level = 25 m
Range of the antenna = dm = 33.9 km
Area covered in transmission = 3608.52 km
Thus, the percentage increase in area covered in case (ii) relative to the case (i) = 348.9 %
If the whole earth is to be connected by LOS communication using space waves (no restriction of antenna size or tower height), what is the minimum number of antennas required? Calculate the tower height of these antennas in terms of earths radius?
Answer:In order to connect earth with LOS using space waves,
Let the height of the antenna receiving the signals be ‘ht’
The ‘ht’ is equal to ‘hr’ where
The line of sight between transmission and receiving antennas be ‘dm’
The maximum distance would be
The maximum frequency for reflection of sky waves from a certain layer of the ionosphere is found to be fmax= 9(Nmax)1/2, where Nmax is the maximum electron density at that layer of the ionosphere.
On a certain day it is observed that signals of frequencies higher than 5 MHz are not received by reflection from the F1 layer of the ionosphere while signals of frequencies higher than 8 MHz are not received by reflection from the F2 layer of the ionosphere. Estimate the maximum electron densities of the F1 and F2 layers on that day.
Answer:The values given in the question are
The formula used is Maximum frequency
So, the Nmax |
Again, after value substitution,
On radiating (sending out) and AM modulated signal, the total radiated power is due to the energy carried by . Suggest ways to minimise the cost of radiation without compromising on the information.
Answer:The overall power radiated because of energy carried by
Since the information is only transmitted by the amplitude modulated signals that are as these sideband frequencies are mainly closer to the carrier frequency, the cost can easily be minimised by transmitting both these signals.
NCERT Exemplar Class 12 Physics Solutions Chapter 15 Long Answer
The intensity of a light pulse travelling along a communication channel decreases exponentially with distance x according to the relation , where I0 is the intensity at is the attenuation constant.
(a) Show that the intensity reduces by 75% after a distance of
(b) Attenuation of a signal can be expressed in decibel (dB) according to the relation .What is the attenuation in dB/km for an optical fibre in which the intensity falls by 50% over a distance of 50 km?
Answer:The given components in the question,
Now, to calculate the % decrease in intensity, the formula used would be
% derease in intensity
(ii) Let be the attenuation in dB/km. If x is the distance travelled by signal, the
So, the final answers for both the parts are,
i) The decrease in the intensity is reduced by 75%.
ii) The attenuation of the given optical fibre = 0.0602 dB/km
A 50 MHz sky wave takes 4.04 ms to reach a receiver via re-transmission from a satellite 600 km above earth’s surface. Assuming re-transmission time by satellite negligible, find the distance between source and receiver. If communication between the two was to be done by Line of Sight (LOS) method, what should size and placement of receiving and transmitting antenna be?
The values given in the question are,
Velocity of waves
Time to reach a receiver
Height of satellite,
Radius of earth
Size of transmitting antenna
By using the formula = distance travelled by wave/time = velocity
The final velocity of waves
After using the Pythagoras theorem,
Thus, the distance between source and receiver
So, the maximum distance from the transmitter to the ground would by the EM waves would be
An amplitude modulated wave is as shown in the figure. Calculate
(i) the percentage modulation
(ii) peak carrier voltage and
(iii) peak value of information voltage
As shown in the figure,
i) Percentage modulation
After substituting the values of Vmax and Vmin, the percentage modulation = 66.67%
ii) the formula of peak carrier voltage is
(i) Draw the plot of amplitude versus ω for an amplitude modulated wave whose carrier wave is carrying two modulating signals,
(ii) Is the plot symmetrical about ? Comment especially about plot in region
(iii) Extrapolate and predict the problems one can expect if more waves are to be modulated.
(iv) Suggest solutions to the above problem. In the process can one understand another advantage of modulation in terms of bandwidth?
ii) No, the plot of the frequency spectrum is not symmetrical due to the crowding for the present in the spectrum
iii) The probability of mixing of signals is very high due to the crowding at
iv) An easy way to accommodate more signals would be to increase the bandwidth and frequency of the carrier waves.
An audio signal is modulated by a carrier wave of 20MHz such that the bandwidth required for modulation is 3kHz. Could this wave be demodulated by a diode detector which has the values of R and C as
Carrier wave frequency,
Therefore, it can be demodulated
Therefore, it can be demodulated
Main Subtopics Covered in NCERT Exemplar Class 12 Physics Solutions Chapter 15 Communication System
- Elements Of A Communication System
- Basic Terminology Used In Electronic Communication Systems
- Bandwidth Of Signals
- Bandwidth Of Transmission Medium
- Propagation Of Electromagnetic Waves
- Ground wave
- Space wave
- Modulation And Its Necessity
- Size of the antenna or aerial
- Adequate power radiated by an antenna Ex 15.7.3 – Mixing up of signals from different transmitters.
- Amplitude Modulation
- Production Of Amplitude Modulated Wave
- Detection Of Amplitude Modulated Wave
NCERT Exemplar Class 12 Physics Chapter Wise Links
NCERT Exemplar Class 12 Physics Solutions Chapter 15 Important Topics For Exams
· A communication system makes the successful transmission of an idea or any other important information among individuals possible.
· NCERT Exemplar solutions For Class 12 Physics chapter 15 moves through communication basics, from a simple voice instruction from one person to another to a transfer of files and pictures using a server. Communication is used in telecommunication networks, relay stations, telephones, computers, mobile, telegraph, etc.
· NCERT Exemplar Class 12 Physics solutions chapter 15 also discusses the types of communication systems, the transmission and altering of signals, terms like bandwidth, attenuation, receiver and modulation, and modulation types.
NCERT Exemplar Class 12 Solutions
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Frequently Asked Question (FAQs) - NCERT Exemplar Class 12 Physics Solutions Chapter 15 Communication System
Question: Why is this chapter important?
This chapter is one of the base chapters for those who want to become electrical and communication engineers.
Question: How to download NCERT exemplar Class 12 physics solutions chapter 15?
One can easily go to the solutions page, click on the link and the solutions will be downloaded in PDF format.
Question: How many questions are solved in this chapter?
Our guides have solved all 30 questions from the NCERT exemplar Class 12 Physics chapter 15 exercise
Question: How can students take help from these NCERT exemplar Class 12 Physics chapter 15 solutions?
Students can understand the topic and also use the solutions as a way to refer to their own answers while practicing before the exam.
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Questions related to CBSE Class 12th
i couldnt clear 1st compartment (which held in August 2022) cbse class 12th so can I give improvement in all subjects which to be held on March 2023. tell me a solution i need more than 75% in class 12th
Yes you can appear for the compartment paper again since CBSE gives three chances to a candidate to clear his/her exams so you still have two more attempts. However, you can appear for your improvement paper for all subjects but you cannot appear for the ones in which you have failed.
I hope this was helpful!
i was not able to clear 1st compartment and now I have to give 2nd compartment so can I give improvement exam next year? plz tell me very much tensed(cbse class 12th)
If you was not able to clear 1st compartment and now you giving second compartment so YES, you can go for your improvement exam next year but if a student receives an improvement, they are given the opportunity to retake the boards as a private candidate the following year, but there are some requirements. First, the student must pass all of their subjects; if they received a compartment in any subject, they must then pass the compartment exam before being eligible for the improvement.
As you can registered yourself as private candidate for giving your improvement exam of 12 standard CBSE(Central Board of Secondary Education).For that you have to wait for a whole year which is bit difficult for you.
Positive side of waiting for whole year is you have a whole year to preparing yourself for your examination. You have no distraction or something which may causes your failure in the exams. In whole year you have to stay focused on your 12 standard examination for doing well in it. By this you get a highest marks as a comparison of others.
Believe in Yourself! You can make anything happen
All the very best.
if i am giving improvement in one subject this year, will i be able to give improvement in more subjects next year?
I appreciate your Interest in education. See the improvement is not restricted to one subject or multiple subjects and we cannot say if improvement in one subject in one year leads to improvement in more subjects in coming year.
You just need to have a revision of all subjects what you have completed in the school. have a revision and practice of subjects and concepts helps you better.
All the best.
I got an RT for 2 subjects, so do I have to give exams for all the subjects in the coming year or just the 2. pls help me
You just need to give the exams for the concerned two subjects in which you have got RT. There is no need to give exam for all of your subjects, you can just fill the form for the two subjects only.
I will have my boards in Feb 2023 (Class 12) and I still havent completed 1 chapter in any subject (Physics, chemistry and maths) , My 11th concepts are not that great but its okish, I wanted to know that If I do start studying from 15th of August Can I get above 85?
If you'll do hard work then by hard work of 6 months you can achieve your goal but you have to start studying for it dont waste your time its a very important year so please dont waste it otherwise you'll regret.