Bangalore University 2007-5th Sem B.Sc Physics IESTER , /e - Question Paper

IV SEMESTER B.Sc. Examination, May/June 2007
(Semester Scheme)
PHYSICS-IV
Acoustics, Optics and Lasers

Time: three Hours Max. Marks: 60

PART-A

ans any 5 of the subsequent ques.. every ques. carries six marks:

1. a) elaborate sound waves?

b) find an expression for the velocity of sound waves in a rod. (1+5)

2. define with necessary theory, the Focault’s rotating mirror method of determining the velocity of light. 6

3. a) discuss the concept of Huygen’s principle and construction of wavefront.

b) elaborate coherent sources? How they are found using a biprism? (3+3)

4. elaborate Newton’s rings? provide the theory of Newton’s rings. (1+5)

5. a) discuss the construction of a zone plate

b) Compare a zone plate with a convex lens. (3+3)

6. a) What is resolving power?

b) find an expression for the resolving power of a grating. (2+4)

7. a) Distinguish ranging from elliptically polarised and circularly polarised light.

b) discuss the terms “optical activity” and “specific rotation” of a substance. (4+2)

8. discuss the construction and working of Ruby Laser.


PART-B

ans any 4 of the subsequent ques.. every ques. carries five marks:

9. Plane waves of sound of effective pressure 100Pa travelling in water incident on a sand bottom. The density of sad is 2000 kg m-3 and speed of sound in sand is 200 m-1. If the density of water is 1000 kg m-3 and velocity of sound in water is 1480 ms-1, compute

a) The effective pressure of reflected wave back into water and
b) The effective pressure of the transmitted wave into the sand.

10. In a biprism experiment interference fringes of width 0.2mm are observed at 1m from the slit. The distance ranging from the coherent sources is 3mm. compute the wavelength of light. On placing a thin transparent sheet of refractive index 1.5 in the path of 1 of the interfering beams the central bright fringe was obtained to be shifted through a distance equal to width of 10 fringes. compute the thickness of transparent sheet.


11. Using sodium light of wavelength 5893 A, interference fringes are formed from a thin air wedge. When viewed normally 10 fringes are observed in a distance of one cm. compute the angle of wedge.

12. A narrow slit illuminated with monochromatic light of wavelength 5893 A is placed at a distance of 0.1 m from a straight edge. If the distance ranging from the straight edge and the screen is 1.9m, compute the distance ranging from the 1st and 4th dark bands.

13. Light of wavelength 5000 A is incident normally on a plane transmission grating of width 3cm and 1500 lines. obtain the angle of diffraction in the 1st order.

14. Plane polarised light passes through a quartz plate with its axis parallel to the
faces. compute the lowest thickness of the plate for which the emergent beam will be

a) Plane polarised and
b) Circularly polarised provided nE= 1.553, no=1.544 and ? = 5000 A.

PART-C

ans any 5 of the subsequent ques.. every ques. carries two marks:

15. a) If the Kundt’s tube is filled with CO2 instead of air, what happens to the length of every loop formed in it? discuss.

b) Can Sound waves be polarised? Expalin.

c) Bubbles of colourless soap solution appear coloured in sunlight. Why?

d) Is the phenomenon of interference of light in accordance with the legal regulations of conservation of energy? discuss.

e) It is easy to observe diffraction effect in sound than in light. Justify?

f) Does the value of polarising angle depend on colour of light? discuss.

g) Optic axis in a doubly refracting crystal is a direction and not a particular line. discuss.

h) If a hologram is broken into fragments, can these fragments provide rise to reconstruction of images? discuss.

Earning:   Approval pending.