University:West Bengal University of Technology
Course: GEOMETRICAL OPTICS
Subjest : GEOMETRICAL OPTICS
Year of Question Paper : 2012
CS/B.OPTM/SEM-1/BO-101/2012-13
2012
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. Choose the correct alternatives for the following :
10 X 1 = 10
i) The refractive index of water with respect to air is
a) 1•30 b) 1•31
c) 1•33 d) 1•32.
ii) The wave theory of light was proposed by
a) Newton b) Planck
c) Huygens d) Brewster.
CS/B.OPTM/SEM-1/BO-101/2012-13
iii) Velocities of light in diamond, glass and water decrease
in which of the following orders ?
a) Water > Glass > Diamond
b) Diamond > Glass > Water
c) Diamond > Water > Glass
d) Water > Diamond > Glass.
iv) When the focal length is infinite, the power will be
a) zero b) infinite
c) 100 d) 10.
v) Convex lens acts like a reading glass, when object is kept
a) at focus
b) at 2F
c) in between 2F and F
d) in between F and optical centre.
vi) Geometrical Optics is also known as
a) Geometry optics b) Co-ordinate optics
c) Ray optics d) Photon optics.
vii) Convex lens is used as slide projector when object is kept
a) at 2F b) in between F and 2F
c) at F d) none of these.
viii) Optical fibre works on the principle of
a) refraction b) total internal reflection
c) reflection d) none of these.
ix) If two thin lenses of powers P 1 and P 2 are kept in
contact then equivalent power is
a) P 1 P 2 b) P 1 – P 2
c) P 1 + P 2 d) none of these.
CS/B.OPTM/SEM-1/BO-101/2012-13
x) Total internal reflection occurs when light travels from
a) rarer to denser medium
b) denser to rarer medium
c) both (a) and (b)
d) none of these.
GROUP – B
( Short Answer Type Questions )
Answer any three of the following. 3 X 5 = 15.
2. Define optical fibre. State the uses of optical fibre.
3. Write a short note on cardinal points of thick lens system.
4. What is total internal reflection ? Mention condition of total
internal reflection. 2 + 3
5. Write a short note on astigmatism.
GROUP – C
( Long Answer Type Questions )
Answer any three of the following. 3 X 15 = 45
6. What is a lens ? Obtain lens makers' formula. Deduce the
formula to find out the equivalent focal length and power
when two convex lenses are mounted coaxially to form a
combination. 2 + 5 + 8
7. a) Derive vergence equation for refraction at a curved
surface.
b) Obtain lens makers' formula for a thin lens. 7 + 8
1208 3 [ Turn over
CS/B.OPTM/SEM-1/BO-101/2012-13
8. a) For a thin prism prove that = ( µ – 1 ) A, where the
symbols have their usual meaning.
b) An image of size d 1 is formed on a screen by a convex
lens. By moving the lens an image of size d 2 is formed
when the object and the screen are fixed. Show that
the size d of the object is given by
d = ( d ) 1 d 2 1/2 .
c) A convex lens of glass ( n = 1•5 ) has radii of curvature
15 cm and 30 cm. Find its focal length in air. What will
be its focal length in water of refractive index 4/3 ?
5 + 5 + 5
9. a) Write the statement of the Fermat's principle.
b) Prove Snell's law of refraction in the light of Fermat's
principle for a plane surface.
c) For a concave spherical surface find out the vergence
equation. 2 + 7 + 6
10. a) Why is matrix method useful in optics ?
b) Differentiate between the following :
i) Step index and graded index fibre
ii) Single mode and multimode fibre.
c) With sketch define
i) Critical angle
ii) Angle of acceptance.
d) A fibre cable has an acceptance angle of 30° and a core
index of refraction of 1•4. Calculate the refractive index
of the cladding. 3 + ( 3 + 3 ) + 3 + 3..
Course: GEOMETRICAL OPTICS
Subjest : GEOMETRICAL OPTICS
Year of Question Paper : 2012
CS/B.OPTM/SEM-1/BO-101/2012-13
2012
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. Choose the correct alternatives for the following :
10 X 1 = 10
i) The refractive index of water with respect to air is
a) 1•30 b) 1•31
c) 1•33 d) 1•32.
ii) The wave theory of light was proposed by
a) Newton b) Planck
c) Huygens d) Brewster.
CS/B.OPTM/SEM-1/BO-101/2012-13
iii) Velocities of light in diamond, glass and water decrease
in which of the following orders ?
a) Water > Glass > Diamond
b) Diamond > Glass > Water
c) Diamond > Water > Glass
d) Water > Diamond > Glass.
iv) When the focal length is infinite, the power will be
a) zero b) infinite
c) 100 d) 10.
v) Convex lens acts like a reading glass, when object is kept
a) at focus
b) at 2F
c) in between 2F and F
d) in between F and optical centre.
vi) Geometrical Optics is also known as
a) Geometry optics b) Co-ordinate optics
c) Ray optics d) Photon optics.
vii) Convex lens is used as slide projector when object is kept
a) at 2F b) in between F and 2F
c) at F d) none of these.
viii) Optical fibre works on the principle of
a) refraction b) total internal reflection
c) reflection d) none of these.
ix) If two thin lenses of powers P 1 and P 2 are kept in
contact then equivalent power is
a) P 1 P 2 b) P 1 – P 2
c) P 1 + P 2 d) none of these.
CS/B.OPTM/SEM-1/BO-101/2012-13
x) Total internal reflection occurs when light travels from
a) rarer to denser medium
b) denser to rarer medium
c) both (a) and (b)
d) none of these.
GROUP – B
( Short Answer Type Questions )
Answer any three of the following. 3 X 5 = 15.
2. Define optical fibre. State the uses of optical fibre.
3. Write a short note on cardinal points of thick lens system.
4. What is total internal reflection ? Mention condition of total
internal reflection. 2 + 3
5. Write a short note on astigmatism.
GROUP – C
( Long Answer Type Questions )
Answer any three of the following. 3 X 15 = 45
6. What is a lens ? Obtain lens makers' formula. Deduce the
formula to find out the equivalent focal length and power
when two convex lenses are mounted coaxially to form a
combination. 2 + 5 + 8
7. a) Derive vergence equation for refraction at a curved
surface.
b) Obtain lens makers' formula for a thin lens. 7 + 8
1208 3 [ Turn over
CS/B.OPTM/SEM-1/BO-101/2012-13
8. a) For a thin prism prove that = ( µ – 1 ) A, where the
symbols have their usual meaning.
b) An image of size d 1 is formed on a screen by a convex
lens. By moving the lens an image of size d 2 is formed
when the object and the screen are fixed. Show that
the size d of the object is given by
d = ( d ) 1 d 2 1/2 .
c) A convex lens of glass ( n = 1•5 ) has radii of curvature
15 cm and 30 cm. Find its focal length in air. What will
be its focal length in water of refractive index 4/3 ?
5 + 5 + 5
9. a) Write the statement of the Fermat's principle.
b) Prove Snell's law of refraction in the light of Fermat's
principle for a plane surface.
c) For a concave spherical surface find out the vergence
equation. 2 + 7 + 6
10. a) Why is matrix method useful in optics ?
b) Differentiate between the following :
i) Step index and graded index fibre
ii) Single mode and multimode fibre.
c) With sketch define
i) Critical angle
ii) Angle of acceptance.
d) A fibre cable has an acceptance angle of 30° and a core
index of refraction of 1•4. Calculate the refractive index
of the cladding. 3 + ( 3 + 3 ) + 3 + 3..
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