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Optics and Spectroscopy - 7BPH3C1
OPTICS AND SPECTROSCOPY 7BPH3C1
Total Marks: 25 Time: 1.0 Hr
SECTION A – SHORT ANSWER - 5 x 2 = 10 Marks
ANSWER ALL THE QUESTIONS
1. Why
the Fraunhofer diffraction is called ‘Far Field Diffraction’?
2. Define
resolving power. State Rayleigh criterion for resolution.
3. Define
circular polarization.
4. Why the
intensity of anti-stokes line less than that of stokes line?
5. What is
molecular polarizability?
SECTION B - DESCRIPTIVE - 3 x 5 = 15 Marks
ANSWER ANY THREE
6. Discuss the
theory of double slit Fraunhofer diffraction.
7. Derive the
Grating equation sinθ = Gmλ.
8. Write the
theory of half wave plate.
9. Explain
vibrational Raman spectra.
10. Explain
infrared spectroscopy.
Optics and Spectroscopy - 7BPH3C1
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OPTICS AND
SPECTROSCOPY 7BPH3C1
DATE: 29.10.2020
Total Marks: 50
Time: 2.0 Hrs
SECTION A - MCQ - 20 x
1 = 20 Marks
1. A biconcave lens consists of
A. Two concave faces in opposite
directions
B. Two concave faces in the same direction
C. A concave and a convex face in
opposite directions D. Two convex faces in opposite
directions
2. Marginal rays are
A. Rays close to the principal axis B. Rays close to the edge of the lens
C. Rays along the principal axis D. Rays through the center of the lens
3. For reducing spherical aberration
using a combination of lenses, the criterion is,
A. d = f1 x f2 B. d = f1 / f2
C. d = f1 - f2 D. d = f1 ̴ f2
Where f1 and f2 are the focal lengths of the lenses and d is the separation between them.
4. Chromatic aberration in lenses is
due to the phenomenon of
A. Dispersion B. Reflection
C. Interference D. Diffraction
5. Which of the following telescope
design greatly reduces the chromatic aberration in image formation?
A. Galilean B. Keplerian
C. Newtonian D. Copyscope
6. Coma is called so since,
A. It’s an acronym B. The image formed looks like a comet
C. It looks like coma D. It’s senseless
7. Dispersion of waves depends on
A. their amplitude B. their wavelength
C. their speed D. All of these three
8. Dispersion in a medium arises due
to the interaction of light waves with
A. the electrons B. the ions
C. the neutrons D. the protons
9. The use of Canada balsam as a
cement in optical instruments is because
A. it’s very hard B. it’s opaque
C. it’s transparent and has nearly same refractive index as glass D. it’s very soft
10. A use of direct vision spectroscope
is
A. Measuring the temperature B. Analyzing the quality of gems
C. Evaluating pressure D. Measuring colors
11. Primary rainbow is formed due to
A. a single internal reflection B. two internal reflections
C. three internal reflections D. none of the others
12. Secondary rainbow’s color order is
A. same as that of the primary rainbow B. inverted to that of the primary rainbow
C. green, red, orange and blue D. red, yellow, blue and orange
13. Condition[s] for sustained
interference between light waves
A. Sources must be coherent B.
Sources must be narrow (of the order of the wavelength)
C. Sources must emit light of same
frequency D. All the other options
14. In the condition for constructive interference
is [Stoke’s rule applicable], the path difference must be
A. Integral multiples of wavelength B. Fractional multiples of wavelength
C. Half odd integral multiples of wavelength D. A single wavelength
15. The vibrant colors of the peacock feathers
is due to
A. polarization B. absorption
C. refraction D. interference
16. A primary application of air wedge
is
A. measurement of intensity B. measurement diameter of a thin wire
C. measurement of chromaticity D. None of the others
17. The interference fringe width
pattern of a surface against an optical is directly related to
A. Area of the surface B. Topography of the surface
C. Volume of the surface D. Global slope of the surface
18. The radii of rings in Newton rings
is directly proportional to
A. square of integers B. reciprocal of integers
C. reciprocal of square root of
natural numbers D.
square root of natural numbers
19. A recent application of Michelson
Interferometer which earned a Nobel Prize is,
A. Observation of Gravitational Waves B. Discovery of Blue LED
C. Birth and Death of Stars D. Discovery of Laser
20. The compensator in Jamin’s
interferometer is used for
A. counting the number of fringes manually B. measuring the wavelength of light
C. measuring the pressure of the gas D. conveniently measuring the refractive index directly
SECTION B - DESCRIPTIVE
- 5 x 6 = 30 Marks
ANSWER ANY FIVE
21. Derive the condition for minimization
of spherical aberration when two thin lenses are separated by a distance.
22. Explain the working of Huygens
eyepiece.
23. Explain the construction and working
of a direct vision spectroscope.
24. Discuss how an aplanatic lens eliminates
spherical aberration.
25. Discuss the theory of formation of secondary rainbow.
26. Describe the effect of interference in reflected
light from thin films.
27. Discuss the theory of air wedge with
neat diagrams.
28. Derive the expression for the radii of the rings formed in Newton rings experiment.
Description: This is a simulation of the processes involved in the formation of a rainbow. The 3D image on the right shows the location of a rainbow as seen by an observer on the ground. The green plane represents the ground. The blue dot on the green plane represents the position of the person viewing the rainbow. Change the angle of the sun above the horizontal and watch how the position of the rainbow changes.
On the right in the 2D view you can see the actual refraction and reflection that occurs in each raindrop. The white light enters the spherical raindrop, and it undergoes refraction (bending) and dispersion (different wavelengths/colors bending by slightly different amounts). Only the extreme red and violet rays are shown. On the right side of the raindrop reflection occurs. Near the bottom of the raindrop the light leaves the drop, again refracting and dispersing. The light from the red end of the spectrum comes out of the drop below the light from the violet end of the spectrum. This confuses some, as red is the color located at the top of a rainbow and violet is on the bottom. You can zoom in on the raindrops in the 3D view (by clicking the button). This view may help people understand this apparent contradiction. The drop that sends the red light to the viewer needs to be higher in the sky than the drop that sends the violet ray to the viewer (with all the other colors in between, of course).
II YEAR – III SEMESTER
COURSE CODE : 7BPH3C1
CORE COURSE VI – OPTICS AND SPECTROSCOPY
Unit I GEOMETRICAL OPTICS
Lens – Spherical aberration in lenses – Methods of minimizing spherical aberration – chromatic aberration in lenses – condition for achromatism of two thin lenses (in and out of contact) – Coma - Aplanatic lens – Eyepieces – Ramsden’s and Huygens’s eyepieces.
Dispersion – Angular and Chromatic dispersion – combination of prisms to produce i)dispersion without deviation ii) deviation without dispersion – Cauchy’s dispersion formula– Direct vision spectroscope – Theory of formation of rainbow.
Unit II INTERFERENCE
Conditions for interference – colours of thin films – Air wedge – theory – determination of diameter of a thin wire by Air wedge – test for optical flatness – Newton’s rings – Determination of refractive index of a liquid.
Michelson’s Interferometer – theory and its Application (Measurement of wavelength and difference between wavelength of two close lines, thickness of mica sheet) – Jamin’s interferometer – determination of refractive index of gases
Unit III DIFFRACTION
Fresnel’s diffraction –Rectilinear propagation of light – zone plate –diffraction at circular aperture – opaque circular disc – Fraunhofer diffraction at single slit – Double slit – Plane diffraction grating – theory and experiment to determine wavelength – overlapping of spectral lines.
Rayleigh’s criterion for resolution – resolving power – resolving power of grating – resolving power of a prism
Unit IV POLARIZATION
Double refraction – Huygens’s explanation of double refraction in uni axial crystals – Nicol Prism – Nicol Prism as polarizer and analyzer – Polaroids and their uses – Quarter wave plates and Half wave plates. Plane, elliptically and circularly polarized light – Production and detection
Optical activity– Fresnel’s explanation of optical activity – Specific rotatory power – determination using Laurent’s half shade polarimeter
Unit V SPECTROSCOPY
Microwave and infrared Spectroscopy – Rotation of molecules – Rotational Spectra – The rigid diatomic molecules, selection rules – the intensities of spectral lines – Infrared spectroscopy (outlines only)
Raman Spectroscopy – Quantum theory of Raman effect – Classical theory of Raman effect – Molecular Polarisability – pure rotational Raman spectra of linear molecules – vibrational Raman spectra – Applications.
Text Books:
Books for Reference: