# Physics Paper III Waves And Oscillations Previous Year Question Paper Year 2006 : IInd Year

**Q. 1.** Distinguish between free and forced vibrations. Give theory of forced damped vibrations. Discuss the condition of resonance.

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**Q.2 Image no. 2**

In the above figure two masses ma and mb are connected by three massless springs of spring-constants k1, k2 and k3 If ma = mb = m and k1 = k2 = k3 = k :

(i) Find frequency of normal modes for longitudinal vibration.

(ii) Find normal co-ordinates for longitudinal vibration.

(iii) Show that the total energy of the system is equal to the sum of energies associated with the two modes.

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**Q. 3. (a) **What is optical path ? State Fermat’s principle and derive laws of reflection based on Fermat’s principle. 4

**(b) **State Huygen’s principle and derive laws of refraction from Huygen’s principle.

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**Q. 4. (a)** What are Newton’s rings and how are they formed? How would you use Newton’s rings to measure wavelength of light? 5

**(b)** In Newton’s rings experiment the diameter of 10th ring changes from 1.5 cm to 1.4 cm when a liquid is introduced between the lens and plate. Calculate the refractive index of the liquid.

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**Q. 5. (a) **What do you mean by Fraunhoffer diffraction ? Describe the Fraunhoffer pattern obtained with a single slit illuminated by a beam of monochromatic light. Deduce condition of maxima and minima.

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**(b) **Calculate the minimum number of lines in a grating which will just resolve the two wavelengths 5890 A 5896 A in its first order.

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**Q. 6. (a)** Describe the construction of a zone plate and explain its working. Explain how it behaves as a lens of multiple foci. 5

**(b)** Distinguish between normal and anomalous dispersion.3

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**Q. 7. (a) **Derive an expression for the equivalent focal length of two lenses separated by a distance. 5

**(b) **Two thin convex lenses having focal lengths 5 cm and 2 cm are co-axial and are separted by a distance of 3 cm. Find the equivalent focal length and position of cardinal points.

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**Q. 8. **Write short notes on any two of the following :

(i) Lissajous figures;

(ii) Melde’s experiment;

(iii) Temporal and spatial coherence;

(iv) Chromatic and spherical aberrations.

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