# PHE-09 Optics Solved Assignment 2018

Course Name: OPTICS

Course Code: PHE-09

Assignment Code: PHE-09/TMA/2018

Medium: English

Category:

## Description

### Assignment Code: PHE-09/TMA/2018

Questions:

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.
b) The wavelength of the electromagnetic wave used for AM broadcasting is 110 m. Calculate the frequency of the wave.
c) Discuss the opponent-process theory of colour vision.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
4. a) Derive an expression to show that the condition of population inversion is necessary for laser action.
b) Compare and contrast three level and four level pumping schemes.
c) With a labelled diagram, discuss the recording a hologram.
d) Explain the propagation of light through optical fibre. What are the advantages of using optical fibres for communication?

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