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?

Raj was cycling from his village to a neighbouring village.On the way, he met an old man who was walking in the direction of the same neighbouring village. Raj invited the old man to sit on his cycle and took him to the neighbouring village.The old man got down from the cycle, thanked Raj and gave him blessing.
Read the above passage and answer the following questions:
(i)  What are the values displayed by Raj?
(ii) Can you relate the given paragraph with the process of modulation?

Anuj's mother was having constant headaches. After a medical check-up, she was diagnosed with tumour. Anuj realized there was a telecommunication tower very close to their house. He enquired from the doctor if the radiation from the tower could have caused the tumour. As the doctor supported his anxiety, he lodged a complaint with the police and ultimately succeeded in getting the tower removed to a distant place away the from residential colony?
Answer the following :
(i)  What values were displayed by Anuj?
(ii) Anuj made a rough estimate about the height of the antenna to be 20 m from the ground. Calculate the maximum distance upto which radiations from the tower are likely to reach. Use the value of radius of the Earth = 6400 x 10³ m.

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.

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?

Seema wants admission in a professional course in a village. It was last date of admission and she left a concerning certificate at home. She became upset as college was very far from the home. She called her brother for it and he faxed the certificate. She got admission and thanked her brother for timely help.
(a) What are the value displayed by Seema and her brother?
(b) What do you mean by Fax?
(c) sky waves are not used in transmitting TV signals.Why?

(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.

Group discussion was arranged in class XII on the topic of atmosphere. Three groups were made. Teacher asked the question "why can Moonbe not used as a communication satellite?" Answers were given by all the three groups. Each, group can give only one reason. Teacher told them that reason given by each group is correct. The groups collected all the three, reasons and came to correct conclusion,"
(i) Give the correct reason for the above question.
(ii) What values were showed by all the three groups?

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