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# PHE-09 Optics Solved Assignment 2019

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Tutor Marked Assignment
OPTICS
Course Code: PHE-09
Assignment Code: PHE-09/TMA/2019
Max. Marks: 100

SKU: PHE-09 EM Categories: ,

## Description

Tutor Marked Assignment
OPTICS
Course Code: PHE-09
Assignment Code: PHE-09/TMA/2019

 Title Name PHE-09 Solved Assignment 2018-19 University IGNOU Service Type Solved Assignment (Soft copy/PDF) Course BSC (PHYSICS) CHE Language ENGLISH Semester 2018-2019 Course: BSC (PHYSICS) CHE Session 2018-19 Short Name PHE-09 (ENGLISH) Assignment Code PHE-09/TMA/2019 Product Assignment of BSC (PHYSICS) 2018-2019 (IGNOU) Submission Date Valid from January 1, 2019 to December 31, 2019 Price RS. 100

1. Answer any four parts: (5×4 = 20)
a) The electrical breakdown in air occurs at electric field strength of 3.5MV m−1
.
Calculate the corresponding intensity of a plane wave.
b) Highlight the advantages offered by Fresnel bi-prism arrangement for observing
interference patterns.
c) Compare the Fraunhofer diffraction patterns of single slit and double slits.
d) Discuss temporal and spatial coherences.
e) Explain light transmission through optical fibres.
2. a) Obtain expressions for reflection and transmission amplitude coefficients when
electric vector associated with a plane monochromatic e. m. wave is in the plane of
incidence. (10)
b) Show that plane polarised light and circularly polarised light are special cases of
elliptically polarised light. (10)
3. a) A double slit interference pattern is produced by a parallel beam of light passing
through two slits of unequal widths 20 λ and 40 λ, respectively, where λ is the
wavelength of the light used. The distance between the centres of the slits is
1,000 λ. If the fringes are observed on a screen far off from the slits (D >> 1,000 λ),
calculate the separation of two adjacent maxima. (10)
b) A plano-convex lens of radius 1.0 m is placed on an optically flat glass plate and is
illuminated by an extended monochromatic source. Assume that the point of contact
is perfect. The diameters of the 15th and 5th dark rings in the reflected light are
.5 90 10 m
−3
× and .3 36 10 m. −3
× Next, the space between the lens and the glass
plate is filled with a liquid. The diameter of the 5th ring changes to 0.3 10 m. −3
×
Calculate the refractive index of the liquid when the ring is (i) dark, and (ii) bright,
if the wavelength of light is 589 nm . (10)
4. a) A plane wave of wavelength 600 nm falls on a long narrow slit of width 0.6 mm.
(i) Calculate the angles of diffraction for the first two minima. (ii) How are these
angles influenced if the width of slit is changed to 0.2 mm? (iii) If a convex lens of
focal length 0.2 m is now placed after the slit, calculate the separation between the
second minima on either side of the central maximum. (10)
4
b) For the arrangement described in 4(a) above, repeat the calculations for the first two
maxima on either side of the central maximum. (5)
c) Use Fresnel construction to discuss diffraction pattern produced by a circular
opaque disc. (5)
5. a) An atomic system, consisting of two energy levels with population of higher energy
level less than that of the lower level, is in thermal equilibrium. Show that the
frequency is introduced into the system. Comment on the consequences of this fact
for laser action. (10)
b) Two energy levels of an atomic system are separated by energy corresponding to
frequency 0.3 10 H .
14 × z Assume that all atoms are in one or the other of these two
energy levels. Compute the fraction of atoms in the upper energy level at
temperature 400 K. Take 23 1
B .1 38 10 J K
− −
k = × and 6.6 10 Js. −34 h = × (5)
c) The refractive indices of the core and cladding materials of an optical fibre are 1.53
and 1.34 respectively. Calculate the numerical aperture and light gathering capacity
of the fibre. (5)

PHE-09, PHE-9, PHE 09, PHE 9, PHE09, PHE9,

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