B.Sc-B.Sc Chemistry (West Bengal Institute of Technology (WBIT), Kolkata-2009)
CS/B.OPTM/SEM-1/BO-101/2009-10
2009
GEOMETRICAL OPTICS ( OPTICS – I )
Time Allotted : 3 Hours Full Marks : 70
The figures in the margin indicate full marks.
Candidates are required to give their answers in their own words
as far as practicable.
GROUP – A
( Multiple Choice Type Questions )
- 1 = 10
- ƒ2 = -ƒ1 b) ƒ2 = -µƒ1
- ƒ1 = - µ ƒ2 d) ƒ1 ƒ2 = -
i) During refraction of light which of the following remains unchanged ?
a) Frequency b) Speed
c) Wavelength d) Intensity.
ii) Total internal reflection occurs when light travels from
a) rarer to denser medium
b) denser to rarer medium
c) both (a) & (b)
d) none of these.
iii) If ƒ1 and ƒ2 represent the first and second focal lengths of a single spherical refracting
surface, then
CS/B.OPTM/SEM-1/BO-101/2009-10
iv) When thin convex lens is put in contact with a thin concave lens of the same focal length, the resultant combination has a focal length equal to
a) ƒ/2 b) 2 ƒ
c) 0 d) none of these.
v) Equivalent power of two thin lenses in contact having
power + 5 D and – 2 D is
a) 7D b) – 7D
c) 3D d) none of these.
vi) A well cut diamond appears bright because
a) it emits light
b) it is radioactive
c) scattering of light
d) total internal reflection of light.
vii) The corpuscular theory of light was proposed by
a) Einstein b) Newton
c) Maxwell d) Huygens.
viii) If for a particular optical system object and image point
can be replaced with respect to each other, then they are called
a) afocal points b) confocal points
c) conjugate points d) none of these.
ix) Critical angle for light passing from glass to air is
minimum for
a) red light b) green light
c) yellow light d) violet light.
x) A converging lens is that which
a) collects rays b) spreads rays
c) forms real image d) forms virtual image.
CS/B.OPTM/SEM-1/BO-101/2009-10
GROUP – B
( Short Answer Type Questions )
Answer any three of the following. 3 X5 = 15
2. a) Define first and second principal focus for spherical
refracting surfaces.
b) Write down different cardinal points of a lens system.
- ä d= ( µ– 1 ) A, where the symbols
have their usual meaning.
4. Write a short note on chromatic aberration.
5. What is total internal reflection ? Mention the conditions of
total internal reflection. 2 + 3
6. Explain the difference between the geometrical path length
and optical path length of a light ray travelling in a medium.
GROUP – C
( Long Answer Type Questions )
Answer any three of the following. 3 X15 = 45
7. a) State and explain Fermat’s principle.
b) Derive laws of refraction using Fermat’s principle.
c) A thin lens of focal length f and refractive index 1·5 is
placed under a liquid of refractive index 1·333. Find the
geometrical focus of a pencil of parallel rays directly
incident upon the lens. 2 + 8 + 5
CS/B.OPTM/SEM-1/BO-101/2009-10
8. a) Derive vergence equation for refraction at a curved surface.
b) Obtain lens makers formula for a thin lens. 7 + 8
9. a) Find the lateral shift by a plane parallel glass plate of
thickness t and refractive index ì.
b) What is dispersion of light ?
c) Briefly explain the structure of an optical fibre. 8 + 2 + 5
10. a) Two thin lenses of focal lengths f 1 and f 2 are kept in
contact. Find the focal length and power of the combination.
b) What is aberration ? What is spherical aberration ? How
can we minimize chromatic aberration ?
c) Three lenses of focal lengths +3D, +5D, – 6D are kept in
contact. Find out the equivalent power and the
equivalent focal length of the combination. 5 + 6 + 4
11. a) Using matrix method in paraxial optics, derive
Translation matrix for a thick lens.
b) What is optical fibre ? Explain the propagation of light
through it.
c) Mention the medical application of optical fibre.
6 + ( 2 + 5 ) + 2
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