Demodulation is the reverse process of modulation, which is performed in a receiver to recover the original modulating signals. At the receiving end, the signals are generally weak due to attenuation in the channel. The receiver selects only the desired signal, rejecting the unwanted (noise) signals and amplifies the same.
Read the above passage and answer the following questions:
(i) What are the main functions of a demodulator?
(ii) Give any two examples of demodulators.
(iii) What does the phenomenon of demodulation imply in day to day life?

Physics teacher in the semiconductor chapter explained that a very low voltage is required for the operation of semiconductor diodes, but Ramesh found that at home the supply used for charging mobile or CD player etc. is 220V. He was confused. Then, he discussed this problem with his classmates and with the teacher. The teacher explained the reason and Mohan was satisfied.
(a) Why is 220V ac supply used in charger and CD player?
(b) What values were displayed by Mohan?

Rita noticed that the transformer in her locality gets damaged quite often leading to long power cuts. She complained to the power distribution company with the help of her father and got the transformer replaced?
(i) What is the principle of a transformer?
(ii) Mention two losses which take place in a transformer.
(iii) Values exhibited by Rita in dealing with the above situation.

Sumeet a 5^th class student observed a coloured film of oil on water when illuminated by white light. He felt happy and surprised to see this. His teacher explained him the reason behind it. The child then gives an example of spreading of kerosene oil on water to prevent malaria and dengue.
(i) What value was displayed by his teacher?
(ii) Name the phenomenon involved.

While watching Discovery channel Sheela was impressed that certain organisms have the ability to sense the field lines of earth's magnetic field. They use this ability to travel from one location to another, Sheela wanted to find the angle of dip at her place. She then mounted the compass on a cardboard and placed it vertically along the magnetic meridian. She was able to measure the angle of dip
(a) What values did Sheela have?
(b) Define the magnetic element of earth.