2 0 2 0
BSc (IV Semester) Examination
PHYSICS
Paper : PHY–241 (Old Course)
[ Modern Physics (Atomic and Nuclear Physics and Special Theory of Relativity) ]
Full Marks : 50
Pass Marks : 35%
Time : Two Hours
Note : 1. Students have to attempt Question No. 1 and any other three questions from Section—A, and any one question from Section—B.
2. The figures in the margin indicate full marks for the questions.
1. (a) State the Bohr quantization condition. 2
(b) Define half-life of radioactive substance and write its expression. 2
(c) What do you mean by thermonuclear reaction? Give one example. 2
(d) Write the difference between a-ray and b-ray. 2
(e) Distinguish between ionization potential and critical potential. 2
2. Using Bohr’s atomic model, derive the expression for energy of electron in
H-atom. 10
3. Describe Millikan’s oil-drop method for determining the change of electron. 10
4. State radioactive disintegration law and derive an expression for number of atoms present at any time. Show it graphically. 10
5. (a) What are nuclear fission and fusion reactions? 2+2=4
(b) What is nuclear chain reaction? What is a nuclear reactor? State its principle and explain its working. 6
6. Write short notes on any two of the following : 5×2=10
(a) Geiger-Nuttall law
(b) Neutrino hypothesis
(c) Bainbridge mass spectrograph
(d) Franck and Hertz experiment
7. (a) Describe Michelson-Morley experiment. Write its conclusion and
significance. 8
(b) State the postulates of special theory of relativity. 2
8. State and prove velocity addition theory. Prove the relation . 5+5=10
