A nuclear reactor is a powerful device, wherein nuclear energy is utilised for peaceful purposes. It is based upon controlled nuclear chain reaction. The nuclear chain reaction is controlled by the use of control rods (of boron or cadmium) and moderators like heavy water, graphite, etc. The whole reactor is protected with concrete walls 2 to 2.5 metre thick, so that radiations emitted during nuclear reactions may not produce harmful effects.
Read the above passage and answer the following questions:
(i) Give any two merits of nuclear reactors.
(ii) What is radiactive waste?
(iii) Why do people often oppose the location site of a nuclear reactor? What do you suggest?

Einstein was the first to establish the equivalence between mass energy. According to him, whenever a certain mass \(\left( \Delta m \right) \) disappears in some process, the amount of energy released is \(E=\left( \Delta m \right) { c }^{ 2 },\) where c is velocity of light vacuum \(\left( =3\times { 10 }^{ 8 }m/s \right) .\) The reverse is also true, i.e., whenever energy E disappears, an equivalent mass \(\left( \Delta m \right) ={ E/c }^{ 2 }\) appears.
Read the above passage and answer the following questions :
(i) What is the energy released when 1 a.m.u. of mass disappears in a nuclear reaction?
(ii) Do you know any phenomenon in which energy materialises?
(iii) What values of life do you learn from this famous relation?

Poonam's mother is diagnosed cancer. The attending physician told her that she has to undergo radiotherapy. While telling her the side effects of the treatment, the doctor told that her beautiful hair may fall and she may become bald. Poonam's mother refuses to get the treatment.
Read the above passage and answer the following questions:
(i) What would you do if you were in Poonam's place?
(ii) What values are associated with your attitude?

Marie Curie and her teacher turned husband Pierre Curie worked hard to extract radium chloride (R_aCl₂) from uranium ore. They succeeded in 192 after a long struggle. About 0.19 g of R_aCl₂ was extracted and its radioactivity was studied. They were awarded by the noble prize, which they shared it which they shared it which they shared it with Henri Becquerel.
Read the above passage and answer following questions:
(i) What are the values shown by Marie Curie and her husband?
(ii) What do you understand by radioactivity? How the half-life period is related to the disintegration constant?
(iii) How is average-life of radioactive element related to half-life?

Shyamsaw his younger brother wondering with a question which deals with emission of light from a vapour lamp. He was anxious to know how different colours wre being emitted by different lights. He also saw mercury and sodium vapour lamps in the Physics lab and was curious to know what is inside the lamps. On seeing his anxiety to know more about it, Shyam explained about absorption of energy and re-emission of photons in the visible region. He also advised him not to touch or break any items in the lab for the knowledge.
Read the above passage and answer the following questions:
(i) What is the moral you derive from Shyam's behaviour?
(ii) Which series in the hydrogen spectrum is in the visible region?
(iii) Write the quality displayed by Shyam's brother.