RGU Question Paper Physics Semester III 2022: Waves and Optics

 

December-2022

B.Sc (III Semester) Examination (CBCS)

PHYSICS

Paper: PHY-GE-003

( Waves and Optics )

Full Marks: 80

Pass Marks: 35%

Time: Three Hours

Note: 1. Answer any four questions from Section A, three questions from Section B and two questions from Section C.
2. The figures in the margin indicate full marks for the questions.

Section-A

Answer any four of the following:

1. What are damped vibrations? Establish the differential equation of motion for damped harmonic oscillator. 2+3=5

2. What is standing wave? Explain briefly group velocity and phase velocity. 2+3=5

3. State and explain Huygen's principle. 5

4. Write the Stokes theorem of phase change on reflection. What do you understand by coherent source? Define interference. 2+1+2=5

5. What is polarization of light? Explain it briefly. 5

6. What do you understand by plane waves and spherical waves? 5

Section-B

Answer any three questions:

7. What do you understand by S.H.M.? A particle is subjected to two S.H. motions of equal frequencies acting along the same direction. Show that the resultant motion is also simple harmonic. 3+7=10

8. Explain analytically the formation of standing wave on a string. 10

9. State Fourier's theorem and mention the conditions under which it holds good. 10

10. What is Fresnel's Biprism? Explain how wavelength of an unknown source can be calculated with Fresnel's Biprism. A Biprism is placed 5 cm from a slit illuminated by sodium light of wavelength λ=5890 A˙. The width of the fringes obtained on a screen 75 cm from the biprism is 9.424×10-2cm. What is the distance between the two coherent sources? 2+6+2=10

11. Discuss in detail the theory of Newton's ring formation by reflected light. Newton's rings are formed by reflection of light of wavelength 600 nm. The diameter of the 10th dark ring is 0.4 cm. Calculate the radius of curvature of the lens used. 8+2=10

Section-C

Answer any two questions:

12. What are Lissajous figures? Discuss the formation of Lissajous figures when two S.H.M's are having frequencies in the ratio 1: 2. Also discuss the various cases when the phase difference between two SHMs is 0°, 90° and 180°. 2+10+3=15

13. Discuss the interference pattern for wedge shaped film produced by reflected light. What do you understand by fringes of equal inclination and fringes of equal thickness. 9+3+3=15

14. What is Fraunhofer diffraction? Explain the Fraunhofer diffraction produced by double slit. 3+12=15

15. Write short notes on any two: 7½x2=15

1. Normal modes of a string
2. Application of Fourier's theorem to sawtooth and square wave
3. Plane, circular and elliptical polarization of light