CBSE Class 12 Physics Atoms and Nuclei chapter notes and important questions

CBSE Class 12 Physics Atoms & Nuclei chapter notes and important questions. There are many more useful educational material which the students can download in pdf format and use them for studies. Study material like concept maps, important and sure shot question banks, quick to learn flash cards, flow charts, mind maps, teacher notes, important formulas, past examinations question bank, important concepts taught by teachers. Students can download these useful educational material free and use them to get better marks in examinations.  Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

ATOMS AND NUCLEI

1. In Bohr's theory of model of a Hydrogen atom, name the physical quantity which equals to an integral multiple of h/2∏?

2. What is the relation between 'n' & radius 'r' of the orbit of electron in a Hydrogen atom according to Bohr's theory / Ans: r α n²

3. Write two important inferences drawn from Geiger-Marsden's experiment.

4. What is the distance of closest approach when a 5 Mev proton approaches a gold nucleus (Z = 79)

5. Two nuclei have mass numbers in the ration 1 : 8. What is the ratio of their nuclear radii ?

6. What is the relation between the radius of the atom & mass number ?

1/3 Ans: size a A

7. What is the ratio of the nuclear densities of two nuclei having mass numbers in the ration 1:4 ?

TWO MARKS QUESTIONS

*1. Define the activity of a given radioactive substance. Write its S. I. unit.

*2 (a) The mass of a nucleus in its ground state is always less than the total mass of its constituents-neutrouns and protons. Explain.

*3 The radioactive isotope D decays according to the sequence 

If the mass number and atomic number of d² are 176 and 71 respectively, What is (i) the mas number (ii) atomic number of D?

*4 Why is it found experimentally difficult to detect neutrinos in nuclear B-decay ?

*5 Draw a plot of potential energy of a pair of nucleons as a function of their separation. What is thhe significance of negative potentail energy in the graph drawn ?

6. If 70% of a given radioactive sample is left un-decayed after 20 days, what is the % of original sample will get decayed in 60 days?

7. How does the neutron to proton ratio affected during (i) decay ii) α decay

8. A radioactive sample having N nuclei has activity R. Write an expression for its half-life in terms of R & N.

Ans: R=Nλ, t_1/2 =0.693/λ =0.693N/R 

9. Tritium has a half-life of 12.5 years against beta decay. What fraction of a sample of pure tritium will remain un-decayed after 25 years?

Ans: N₀ /4

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