KNU 4th SEMESTER IMPORTANT QUESTIONS ( WAVES AND OPTICS)

KAZI NAZRUL UNIVERSITY

IMPORTANT QUESTIONS (WAVES AND OPTICS)

SEMESTER -IV

1. What are the beats? Give an analytical description of the phenomenon of beats and show that the beat frequency is equal to the difference between the frequencies of the component oscillators.

2. Two simple harmonic motions act simultaneously on a particle at right angles to each other. Show that the path of the particle will be an ellipse when the two motions have the same period but different amplitudes and initial phases. What happens when the phase difference between the motions is – i) zero ii) 90 degree iii) 180 degree?

3. What are Lissajous figures? Write down their importance.

4. Discuss the formation of Lissajous figures by the superposition of two simple harmonic motions when i) the periods are the same but the amplitudes and phases are different.ii) the periods are in the ratio 1:2, and amplitudes and phases are different.

5. What are the progressive waves? Derive the mathematical equation for a progressive wave.

6. Derive the differential equation of a progressive wave.

7. Define the particle and wave velocities of a wave. Derive the relation between them for a progressive wave.

8. Write down the differences between particle and wave velocity of a wave.

9. Derive an expression for the intensity of a plane progressive harmonic wave. Explain clearly what you mean by ‘Bel’ and ‘Phon’.

10. Define interference of light? State the conditions for the production of sustained interference.

11. Derive the conditions for constructive and destructive interferences? Show that energy remains conserved in case of interference?

12. Describe how the wavelength of monochromatic light can be measured with Fresnel’s biprism.

13. Give the theory of Newton’s rings and show how the wavelength of monochromatic light can be determined with its help.

14. What do you mean by coherent sources? Why two independent sources can’t be coherent?

15. Why very thin films appear coloured?

16. Why is it necessary to use a narrow source for Fresnel’s biprism and extended source for Newton’s ring experiment?

17. Describe the working principle of Michelson’s interferometer. Under what conditions are circular and straight fringes produced by it?

18. Describe the basic principle on which a Fabry-Perot interferometer works.

19. What do you mean by the diffraction of light? Write down the differences between interference and diffraction.

20. Distinguish between Fresnel and Fraunhofer class of diffraction.

21. What is Fresnel’s half period zone? Why is it so-called?

22. What is a zone plate? Explain its action as a convex lens. Derive an expression for its focal length. Also, point out the differences between the convex lens and zone plate.

23. Find an expression for intensity of Fraunhofer diffraction pattern due to a single slit. Discuss the conditions for maxima and minima.

24. Obtain the intensity expression for the Fraunhofer diffraction pattern of a double slit. Deduce the conditions for maxima and minima. What is missing order in a double-slit pattern?

25. State Rayleigh criterion of resolution and discuss its significance.

26. What is grating? Derive an expression for the resolving power of a plane transmission grating.

27. What do you mean by resolving power of a microscope? On what factors does it depend?

28. What do you mean by the polarization of light? Can a sound wave show the phenomenon of polarization?

29. What is the angle of polarization? State and establish Brewster’s law.

30. What is double refraction? How can you use it to obtain a plane-polarized light?

31. State and explain Malus’s law.

32. What is the optical activity? What do you mean by optically active substances? Define specific rotation.

33. What is a quarter-wave plate and a half-wave plate? Explain how a quarter-wave plate can be used to analyze-i) a circularly polarized light and ii) an elliptically polarized light.

34. Explain the terms- Optic axis, Positive and Negative crystals, Principal section of a crystal, E-rays, and O-rays.

35. How can you distinguish between an un-polarized light and circularly polarized light?

36. How quarter-wave plates are used to produce elliptically and circularly polarized light?

37. What do you mean by polaroids? State their uses.