CLICK HERE TO DOWNLOAD THE QUESTION AS A PDF
ALAGAPPA UNIVERSITY
KARAIKUDI – 630 003
UNIT BASED ONLINE EXTERNAL EXAMINATION - OCTOBER – 2020
THIRD SEMESTER SLOT – I
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.