PHE-09 OPTICS in English Solved Assignment 2019

PHE-09 Solved Assignment 2018-19

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Tutor Marked Assignment
Course Code: PHE-09
Assignment Code: PHE-09/TMA/2018
Max. Marks: 100

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Title NamePHE-09 Solved Assignment 2018-19
Service TypeSolved Assignment (Soft copy/PDF)
Language ENGLISH
Semester2018-2019 Course: BSC (PHYSICS) CHE
Short Name PHE-09 (ENGLISH)
Assignment CodePHE-09/TMA/2019
ProductAssignment of BSC (PHYSICS) 2018-2019 (IGNOU)
Submission DateValid from January 1, 2019 to December 31, 2019


Note: Attempt all questions. Symbols have their usual meanings. The marks for each
question are indicated against it. Your answers to descriptive questions should be in
your own words.
1. a) State Fermat’s principle. On the basis of this principle, show that when light passes
from a medium of lower refractive index to a medium of higher refractive index, it
bends towards the normal to the interface between the two media. (7)
b) The wavelength of the electromagnetic wave used for AM broadcasting is 110 m.
Calculate the frequency of the wave. (3)
c) Discuss the opponent-process theory of colour vision. (5)
d) What do you understand by birefringence? What are distinguishing feature of the o−
and e− rays? Draw a diagram showing o− and e−wave surfaces. (6)
e) Unpolarised light is incident on two polarizing sheets placed over one another. The
intensity of light transmitted finally is one-third of the intensity of the incident light.
Calculate the angle between the transmission axes of the two polarizing sheets. (4)
2. a) Obtain the conditions for observing maxima and minima in a Young two-slit
interference pattern. Show that these conditions change when a thin transparent
sheet of thickness t and refractive index µ is introduced in the path of one of the
superposing beams. (5+5)
b) Newton’s rings are formed with reflected light of wavelength 589 nm using a planoconvex
lens and a plane glass plate with a liquid between them. The diameter of the
15th ring is 5.1 mm and radius of curvature of the curved surface of the lens is 1 m.
Calculate the refractive index of the liquid if the ring is dark. (5)
c) A light of amplitude ‘a’ is incident obliquely on a parallel thin film. If ‘r’ and ‘t’
represent the fractions of incident light reflected and transmitted respectively, draw a
diagram to explain multiple reflection of incident light and write the amplitudes of
successive rays. (5)
d) A thin film of glass of refractive index 1.5 is inserted in one arm of Michelson
Interferometer. Calculate the thickness of the film if a shift of 10 fringes is observed.
The wavelength of the light used is 589 nm. (5)
3. a) What is a zone plate? How does a positive zone plate differ from a negative zone
plate? Show that each Fresnel half period zone has nearly the same area. (2+2+6)
b) The diffraction pattern due to a single slit of width 0.4 cm is obtained with the help
of a lens of focal length 30 cm. If wavelength of the light used is 589 nm, calculate
the distance of the first dark fringe and the consecutive bright fringe from the axis. (5)
c) Sodium light is incident normally on a grating of width 4×10−3m. The total number
of lines on the grating is 2000. Determine the angular separation between the sodium
D-lines in the first order spectrum. (5)
d) A single slit has a width of 0.04 mm. A parallel beam of light of wavelength 560 nm
is incident normally on it. If the distance between the slit and the screen is 100 cm,
calculate the separation between the central maximum and the second minima in the
diffraction pattern. (5)
4. a) Derive an expression to show that the condition of population inversion is necessary
for laser action. (7)
b) Compare and contrast three level and four level pumping schemes. (5)
c) With a labelled diagram, discuss the recording a hologram. (5)
d) Explain the propagation of light through optical fibre. What are the advantages of
using optical fibres for communication?

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