Indira Gandhi National Open University (IGNOU) 2005 B.Sc Physics Optics - Question Paper
PHE 9
Temv-End Examination December, 2005 PHYSICS PHE'9 : OPTICS
Time : 2 hours Maximum Marks ; 50
Note : Atl questions are compulsory. The marks for; each question are indicated against it You con use log tables and calculator.
I. Attempt any eight of the following ; 8x2=16
(i) Under what condition can light waves be idealized as rays ?
(ii) Mention any two unique features of a laser and state how these can be exploited in various applications,
(iii) Give one example each of a uniaxial crystal and a biaxial crystal.
{iv) Which are the two classes of diffraction ? How do you distinguish them ?
(v) What is the difference between hue and colour ?
(vi) Explain why the sunlight reflected from a soap film appears coloured,
(vii) Is it possible to obtain Newtons rings with a bright centre ? Explain,
(viii) A ray of light is incident on the surface of a glass plate of refractive index 1'5 at the polarising angle. What is the angle of refraction ?
Ox) How is spatial coherence ensured in double slit interference experiment ?
(x) What is a step-index fibre ?
2. Attempt any two of the following i 2x5=20
(a) Explain how the Michelson interferometer can be used to determine the refractive index of a gas.
(b) Explain, with the help of a diagram, how a holographic microscope functions. How is it different from a conventional high power microscope ?
(c) List the processes involved in image formation by human eye. Describe any two of these.
(a) A plano-convex lens of radius 2 m is placed on an optically plane glass plate. The system is illuminated by monochromatic light and in the transmitted system, the radius of the 7 ring is observed to be 0*52 cm. Calculate the wavelength of the monochromatic light.
(b) Plane waves from a He - Ne laser with wavelength 6300 A are incident on a circular aperture of diameter 0*5 mm. What is the angular location of the first minimum in the diffraction pattern ? Also calculate the diameter of Airy disc on a screen 10 m behind the aperture.
(c) Sodium light is incident normally on a grating of
_o
width 3*5 x 10 m. The total number of lines on the grating is 2000* Determine the angular separation between the sodium Wines = 5890 A and 2 5896 A) in the first order spectrum.
(d) In an experiment with Michelsons interferometer, the scale readings for a pair of positions of maximum indistinctness were found to be 0-6939 mm and 0'9884 mm. The mean wavelength of the two components of the sodium D-light used in the experiment is 5893 A. Deduce the difference between the wavelength of the components.
PHE-9 3 P.T.O.
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