# PHE 9 by kishorkna

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BACHELOR OF SCIENCE (B.Sc.)
00
v—i                   Term-Fld Examination

) Inc.,. 2011
CD
PHYSICS
PIT-.{) : OPTICS

Time : 2 hours                               Maximum Marks : 50
Note : All questions aw compulsory hat there are internal
choices. The fOr each question are indicated
against it. You cm' use lu tables or a calculator. Symbols
have their usual meimings.

1.   Attempt any five pdris :                               2x5 =10

(a)      For a double slit interference experiment,
what is the nature/shape of fringes
obtained on the screen ? Plot the intensity
distribution us a function of phase
difference.

(b)      The energy ncated by the sun per second
is 4 x 1026 Js It the sun is a sphere of
radius 7x 10' km, calculate the Poynting
vector at its s-, li face,

(c)      When sunlight is R;ident on the surface of
a calm pond water at an angle of 3T, the
reflected light is completely polarised.
Justify.

PHE-9                             1                           P,1 .0.
(d)   The resolving power of a Fabry - Perot
interferometer for normal incidence is
5.42 x105. Calculate the separation
between the wavelengths that can be just
resolved at X=500
(e)   List two important characteristics of single
slit Fraunhofer diffraction pattern.
(f)   To penetrate deeper in space, we use
telescopes with objectives of larger aperture.
Justify this statements on physical basis.
(g)   light of wavelength 400 rim has a wavetrain
30 X long. Calculate coherence time.
(h)   Draw energy level diagram of Nd ion in
Nd : YAG laser.

2.   Answer any two parts :                            5x2=10
(a) Consider two light waves of unequal 3+2
amplitudes and having an arbitrary phase
difference, moving along the Z-direction.
Their electric field vectors are mutually
orthogonal. Show that (i) their superposition
leads to an elliptically polarised light and
(ii) linear polarisation and circular
polarisation states are special cases of elliptic
polarisation.
(11) Starting from Maxwell's field equations in        5
free space, show that light waves are
electromagnetic in nature.
(c)  (i)   Interference pattern is obtained by 3+2
division of wavefront as well as
division of amplitude. Explain.
(ii) List one instrument used to observe
each type of pattern.

PHE-9                         2
3.   Answer any one part :                         10x1=10
(a) (i)   Explain the formation of Newton's 4+3
rings and discuss how these can be
used to determine wavelength of light.
(ii) Tn a Newton's rings experiment, the        3
diameters of the 5th and 15th rings are
0.336 cm and 0.590 cm, respectively.
Calculate the radius of curvature of
the piano-convex lens if light of
wavelength 5890 A is used.
(b)   Explain the principle of Fabry-Perot
interferometei. Derive an expression for the
intensity of transmitted light and discuss
sharpness of fringes. Flow is it superior to
Michelson interferometer ?                  3+5+2
4.   Answer any one part :                        10x1=10
Discuss spatial evolution of Fresnel
diffraction pattern to Fraunhofer
diffraction.                          3+5+2
Show that a zone plate acts like a
multi-foci converging lens.
A zone plate is illuminated by light of
wavelength 5500 A . If radii of zone
plate are expressed in cm and given
-
by the relation ru =0.1 N/i, calculate
the location of first focal point.
Discuss Rayleigh's criterion for
resolving two images.                3+4+3
Obtain an expression for resolving
power of a microscope.
Explain why we have to use an
electron microscope to study finer
details of crystal structures.

PHE-9                        3                       P.T.O.
5.   Answer any one part :                           10)(1=10
(a)   Derive expressions for Einstein's A and B 5+5
coefficients. Explain how Finsiein's
prediction of population inversion was
realised in actual practice by Maiman.
(b)   (i)   Holography is better than photography. 5
Discuss on the basis of the processes
involved.
(ii)   Discuss salient features of a hologram. 24.3
With the help of a schematic diagram,
explain the process of image
reconstruction.

PHE-9                         4
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PHE.-9                                               7                                               P.T.O.
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PHE-9                                    8

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