RGU Question Paper Physics Semester IV 2020: Physical Optics and Modern Physics

 

2 0 2 0

BSc (IV Semester) Examination

PHYSICS

Paper : PHY–241 (New Course)

( Physical Optics and Modern Physics )

Full Marks : 60

Pass Marks : 35%

Time : Two Hours

Note : 1. In Section—A any three questions are to be answered. In Section—B any three questions are to be answered.
2. The figures in the margin indicate full marks for the questions.

Section—A

( Physical Optics )

1. (a) Discuss the theory of interference mathematically. Find the condition for constructive and destructive interference.

(b) Establish Stokes’ formula for division of amplitude. 7+3=10

2. (a) What do you mean by Fresnel half period zone? Explain diffraction through a slit by Fresnel half-period zone.

(b) Discuss interference in a wedge shaped film. 7+3=10

3. (a) Distinguish between Fresnel and Fraunhofer diffraction.

(b) Find the expression for intensity of light due to diffraction in a singleslit. Hence draw the single-slit diffraction pattern. 3+7=10

4. (a) Explain the terms spontaneous emission and stimulated emission. Write the expression for Einstein’s coefficient.

(b) Discuss the production of Ruby laser. 6+4=10

5. Write short notes on any two of the following : 5×2=10
(a) Zone plate
(b) Fabry-Perot interferometer
(c) Transmission grating
(d) He-Ne laser

Section—B

( Modern Physics )

6. Describe Thomson’s method of determination of (e/m) of electron. 10

7. Explain the principle, construction and working of a Bainbridge mass spectrograph. Mention its application. 10

8. Describe Frank and Hertz experiment. How does it establish the result of Bohr’s
theory? 10

9. (a) What transformation takes place by emission of $\alpha$-ray, $\beta$-ray and $\gamma$-ray? 5

(b) Discuss the neutrino hypothesis of $\beta$-decay. 5 

10. Write short notes on any two of the following : 5×2=10
(a) Geiger-Nuttall law
(b) Carbon dating
(c) Gamma-rays and their origin
(d) Bohr atomic model