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BSc (VI Semester) Examination
PHYSICS
Paper : PHY–361 (Old Course)
( Atomic Physics and Nuclear Physics )
Full Marks : 80
Pass Marks : 35%
Time : Three Hours
Note : 1. Answer any four questions from Section—A and any four questions from
Section—B.
2. The figures in the margin indicate full marks for the questions.
1. (a) What are the direct origins that lead to arise the fine structure of atomic spectral lines? 2
(b) What is Bohr magneton? 2(c) State the postulates of Bohr’s theory. 3
(d) In the Bohr model, explain how an electron can have a negative amount of energy. 3
2. (a) Distinguish between Zeeman and Paschen-Back effect. 2
(b) Outline the theory of Paschen-Back effect in one-electron system. 8
3. (a) Explain why the normal Zeeman effect is observed only in atoms with an even number of electrons. 3
(b) Describe non-relativistic Sommerfeld theory of hydrogen atom. 7
4. (a) State Moseley’s law. 2
(b) Explain briefly how Moseley’s law can be derived from Bohr’s theory. 8
5. (a) Giving energy level diagram, explain the origin of various series of characteristic X-rays. 6
(b) If X-rays of 0·5 A are detected at an angle of 5° in the first order, what is the spacing between the adjacent planes of a crystal? At what angle will the second order maximum occur? 4
6. Write short notes on any two of the following : 5×2=10
(a) Ritz combination principle
(b) Stern-Gerlach experiment
(c) Quantum theory of Raman effect
(d) Compton effect
7. (a) Explain why heavy nuclei are unstable. 4
(b) Discuss the differences between the liquid-drop model and the independent particle model of the nucleus. 6
8. (a) If a nucleus has a half-life of one year, does that mean it will be completely decayed after two years? Explain. 1+2=3
(b) Explain the working principle of gas filled detectors. 3
(c) What are the differences between hadrons and leptons? 4
9. (a) Justify the statement, “all baryons and mesons are colourless”. 4
(b) Describe briefly the primary and secondary types of cosmic rays with their compositions. 6
10. (a) Describe the construction and working principle of an ionisation
chamber. 8
(b) Write two applications of the ionisation chamber. 2
11. (a) Write Bethe-Weizsäcker mass formula for nuclear models and give two applications of the mass formula. 4
(b) Explain briefly why many heavy nuclei undergo alpha decay but do not spontaneously emit neutrons or protons. 6
12. Write short notes on any two of the following : 5×2=10
(a) Yukawa’s meson theory
(b) East-west effect on cosmic rays
(c) Odd-even rules of nuclear stability
(d) GM counter
