Mohan went to the market to purchase a TV set. He got confused with so many features and functions of electronic appliances. He took the help of his friend Sohan, a science student.Sohan explained him about the communication system, digital and analog signals. This knowledge proved of great help to Mohan in purchasing a colour TV.
Read the above passage and the answer the following questions:
(i)  What do you mean by the term communication?
(ii) Which type of signals are better?
(iii) What type of nature Sohan has?
(iv)What is the minimum number of communication satellites required for global communication coverage?

In the famous conversation, Rakesh Sharma, the first Indian Astronaut in space, was asked by the Prime Minister Indira Gandhi as to how India looked from space.To which he replied,'Sare Jahan Se Achcha' (better than the whole world).
Read the above passage and answer the following questions:
(i)   Which scientific mode of communication enabled the Prime Minister to speak to the Astronaut?
(ii)   Name the scientific values displayed in this anecdote.
(iii) Which values are being reflected in the reply given by the astronaut?
(iv) Give one more example of this scientific mode of communication in everyday life situations.

Arnab was talking on his mobile to his friend for a long time. After his conversation was over, his sister Anita advised him that if his conversation was of such a long duration, it would be better to talk through a land line.
Answer the following questions :
(a) Why is it considered harmful to use a mobile phone for a long duration?
(b) Which values are reflected in the advice of his sister Anita?
(c) A message signal of frequency 10 kHz is superposed to modulate a carrier wave of frequency 1 MHz. Determine the sidebands produced.

Sweta had no proper knowledge about point-to-point communication and broadcast. So, she took help from her friend Rakhi explained him that in point-to-point communication mode, the communication takes place over a link between a single transmitter and a receiver. The example of this mode of communication is telephony. But in broadcast mode, there are a number of receivers corresponding to a single transmitter. The examples of this mode of communication are radio and television. Then Sweta was convinced with answer of Rakhi,
(a) What are the values displayed by Rakhi?b
(b) A message signal of frequency 10 kHz and peak voltage of 10 V is used to modulate a frequency of 1 MHz and peak voltage of 20 V. Determine
(i) modulation index
(ii) frequency of the side band produced.

When Sunita, a class XII student, came to know that her parents are planning to rent out the top floor of their house to a mobile company she protested. She tried hard to convince her parents that this move would be a health hazard.
Ultimately her parents agreed :
(i)  In what way can the setting up of transmission tower by a mobile company in a residential colony prove to be injurious to health?
(ii)  By objecting to this move of her parents, what value did Sunita display?
(iii)  Estimate the range of e.m. waves which can be transmitted by an antenna of height 20m. (Given radius of the earth = 6400 km)

One day Samir though if Moon is a natural satellite then why there is need of other artificial satellites. finally, he came to the conclusion that Moon cannot be used as a communication satellite. So, he requested his teacher for its answer.The teacher explained him the the reasons behind it properly, after which he shared his knowledge with his classmates.
(a) What are the value shown by Samir?
(b) Why can Moon be not as a communication satellite?

(a) Distinguish between sinusoidal and pulseshaped signals.
(b) Explain, showing graphically, how a sinusoidal carrier wave is superimposed on a modulating signal to obtain the resultant amplitude modulated (AM) wave.

Due to regular constant headaches, Anuj's mother in a medical check-up was diagnosed with tumour. With this, Anuj realized that there was a telecommunication tower, which is every close to their house. After enquiring from the doctor about the cause of tumour because of the antenna radiation, Anuj lodged a complaint with the police and finally succeeded in getting the tower removed from the nearby place to distant place away from his residential location.
Answer the following
(i) What values were displayed by Anuj?
(ii) Anuj made a rough estimate about the height of the antenna to be about 20m from the ground. Calculate the maximum distance up to which radiations from the tower are likely to reach. Use the value of radius of the Earth =6400 x 10³ m

What is the length of Marconi antenna for a transmission frequency of 15 MHz?

An audio signal of 15000 Hz modulates a carrier generated by a tank circuit containing 1 nF capacitor and 10 microhenry inductor. Calculate the frequencies of first pair of side bands.