GEOMETRICAL OPTICS

1. When a ray light enters a glass slab from aira) its wavelength decreases b) its wavelength increasesc) its frequency increases d) neither wavelength nor frequency changes

2. When a point object is seen by an observer through a glass slab, the image isa) seen nearer to the observer, but beyond the slab b) at the same distance from the observer as the object isc) seen farther from the observer d) seen near to the observer but between the slab and the observer

3. If ijµ represents the refractive index when a light ray goes from medium 'i' to medium 'j' then the product µ µ µ21 32 43× × is equal to

a) µ32 b) µ42 c) µ31 d) 1/µ14

4. A well cut diamond appears bright becausea) it emits light b) it is radioactive c) of total internal reflection d) it has high density

5. One can not see through fog becausea) fog absorbs light b) light is scattered by the droplets in a fogc) light suffers total reflection at the droplet in a fog d) the refractive index of fog is infinity

6. A driver in a swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his water proof flash lighta) he must direct the beam vertically upwardsb) he has to direct the beam horizontallyc) he has to direct the beam at an angle to the vertical which is slightly less than the critical angle of incidence for total internal reflectiond) he has to direct the beam at an angle to the vertical which is slightly more than the critical angle of incidence for total internal reflection

7. A ray of light travelling inside a rectangular glass block of refractive index 2 is incident on the glass-air surface at an angle of incidenceslightly less than 45°. The refractive index of air is one. Under these conditions the raya) will emerge into the air without any deviation b) will be reflected back into the glassc) will be absorbed d) will emerge into the air with an angle of refraction equal to 90°.

8. The critical angle for light going from medium X into medium Y is θ . The speed of light in medium X is v. The speed of light in medium Yis

a) v ( cos )1− θ b) v / sinθ c) v / cosθ d) v cosθ9. Monochromatic light of wavelength 1λ travelling in a medium of refractive index n1 enters a denser medium of refractive index n2. The

wavelength in the second medium is

a) 1λ ( n1 / n2 ) b) 1λ ( n2 / n1 ) c) 1λ ( n1 - n2 ) / n2 d) 1λ ( n2 - n1 ) / n1

10. A beam of light is converging towards a point I on a screen. A plane parallel plate of glass whose thickness is in the direction of beam = t,refractive index = µ is introduced in the path of the beam. The convergence point is shifted by

a) t 1 1−FHGIKJµ away b) t 1 1

+FHGIKJµ away c) t 1 1

−FHGIKJµ nearer d) t 1 1

+FHGIKJµ nearer

11. A ray of light from a denser medium strikes a rare medium at angle of incidence i (see figure). The reflected and refracted rays make anangle of 90° with each other. The angles of reflection and refraction are r and r'. The critical angle is

a) )r(cotsin 1− b) sin (tan )−1 i c) sin (tan ' )−1 r d) tan (sin )−1 i

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12. Keeping the incident ray fixed, if a plane mirror is rotated through an angle θ about an axis lying in its plane, then the reflected ray turns throughangle

a) 0 b) 2θ c) θ / 2 d) 4θ

13. A plane glass slab is placed over various coloured letters. The letter which appears to be raised the least is

a) violet b) yellow c) red d) green

14. A vessel of depth 2d cm is half filled with a liquid of refractive index 1µ and the upper half with a liquid of refractive index 2µ . The apparent depthof the vessel seen perpendicularly is

a)µ µµ µ

1 2

1 2+FHG

IKJ d b)

1 1

1 2µ µ+

FHG

IKJ d c)

1 1 21 2µ µ+

FHG

IKJ d d)

1 21 2µ µFHGIKJ d

15. A lens forms a sharp image on a screen. On inserting a parallel-sided slab of glass between the lens and the screen it is found necessaryto move the screen a distance d away from the lens in order for the image to be again sharply focused. If the refractive index of glassrelative to air is µ , then the thickness of the slab is

a)dµ

b)µd

c)µµd

( )−1d)

( )µµ−1 d

16. A bird in air looks at a fish vertically below it and inside water. h1 is the height of the bird above the surface of water and h2, the depth of thefish below the surface of water. If refractive index of water with respect to air be µ , then the distance of the fish as observed by the bird is

a) h h1 2+ b) h h1

2+µ

c) µh h1 2+ d) µ µh h1 2+

17. A fish is a little away below the surface of a lake. If the critical angle is 49°, then the fish could see things above the water surface within anangular ring of °θ where

a) θ = 49° b) θ = 90°

c) θ = 98° d) θ = 24½°

18. A short linear object of length L lies on the axis of a spherical mirror of focal length f at a distance ufrom the mirror. Its image has an axial length 'L' equal to

a) Lf

u f−LNMOQP

1 2/

b) Lu ff

( )/

+LNM

OQP

1 2

c) Lu ff

( )−LNM

OQP

2

d) Lf

u f( )−LNM

OQP

2

19. A concave mirror of focal length f produces an image n times the size of the object. If the image is real then the distance of the object fromthe mirror is,

a) ( )n f−1 b) {( ) / }n n f−1 c) {( ) / }n n f+1 d) ( )n f+1

20. In a concave mirror an object is placed at a distance x1 from the focus and the image is formed at a distance x2 from the focus. Then thefocal length of the mirror is

a) x x1 2 b) x x1 2 c) ( ) /x x1 2 2+ d) x x1 2/

21. A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screena) half the image will disappear b) complete image will disappearc) intensity of image will increase d) intensity of the image will decrease

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22. A double convex lens made of material of refractive index 1.5 and having a focal length of 10 cm is immersed in a liquid of refractive index 3.0.The lens will behave asa) converging lens of focal length 10 cm b) diverging lens of focal length 10 cmc) converging lens of focal length 10/3 cm d) converging lens of focal length 30 cm

23. Two lenses of power + 12 and -2 diopters are placed in contact. What will be the focal length of the combinationa) 10 cm b) 12.5 cm c) 16.6 cm d) 8.33 cm

24. f B and f R are the focal lengths of a convex lens for blue and red light respectively and BF and RF are the focal lengths of a concave lensfor blue and red light respectively. We must then havea) f f F FB R B R< <and b) f f F FB R B R< >and c) f f F FB R B R> >and d) f f F FB R B R> <and

25. When a pencil of white light which is parallel to principal axis, is refracted by a converging lens, then the rays converge on the principal axis,the focus point being spread out over a short range along the principal axis. If a screen is put perpendicular to the principal axis, at thefarthest focus point, the image on the screen isa) a sharp white or violet point b) a sharp red pointc) a circular dispersed patch, red at the centre and violet at the border d) a circular dispersed patch, violet at thecentre and red at the border.

26. A real image is formed by a convex lens. A concave lens is now placed adjacent to the convex lens, again the real image is formed. Thiswilla) shift towards the lens system b) shift away from the lens systemc) remain in its original position d) shift to infinity

27. A concave mirror and a convex lens are of the same focal length in air. When they are immersed in watera) the concave mirror will have its focal length increased b) the convex lens will have its focal length increased.c) they will have equal focal lengths, different from those in air d) they will have equal focal lengths, same as those in the air.

28. A thin lens has focal length f, and its aperture has diameter d. It forms an image of intensity I. Now, the central part of the aperture uptodiameter d / 2 is blocked by an opaque paper. The focal length and image intensity will change toa) f /2 and I/2 b) f and I/4 c) 3f /4 and I/2 d) f and 3I/4

29. The least distance between a point object and its real image formed by a convex lens of focal length F isa) 2F b) 3 F c) 4 F d) greater than 4 F

30. A convex lens of focal length A and a concave lens of focal length B are placed in contact. The focal length of the combination is

a) ( A + B ) b) ( A - B ) c)ABA B( )+ d)

ABB A( )−

31. A convex lens of focal length f is placed some where in between an object and a screen. The distance between the object and the screenis x. If the numerical value of the magnification produced by the lens is m, the focal length of the lens is

a) ( )21+mmx

b)mxm( )−1 2 c)

( )mm

x+1 2

d)( )mm

x−1 2

32. A converging lens of focal length 'f ' is placed at a distance 0.3 m from an object to produce an image on a screen 0.9 m from the lens. Withthe object and the screen are in the same positions, an image of the object could also be produced on the screen by placing a converginglens of focal lengtha) f at a distance 0.1 m from the screen b) f at a distance 0.3 m from the screenc) 3f at a distance 0.3 m from the screen d) 3f at a distance 0.1 m from the screen

33. A ray of light falls on the surface of a spherical paper weight making an angle α with the normal and is refracted in the medium at an angleβ . The angle of deviation of the emergent ray from the direction of the incident ray is

a) )( β−α b) )(2 β−α c) 2/)( β−α d) )( α−β

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34. A person can not see the objects clearly placed at distances more than 40 cm. He is advised to use lens of powera) - 2.5 D b) + 2.5 D c) - 6.25 D d) + 1.5 D

35. A double convex lens of focal length 6 cm is made of glass of refractive index 1.5. The radius of curvature of one surface is double that ofthe other surface. The value of small radius of curvature isa) 6 cm b) 4.5 cm c) 9 cm d) 4 cm

36. A parallel beam of monochromatic light is incident on one face of an equilateral prism, the angle of incident being 55°. The angle ofemergence of the beam from the other face is 46°. The angle of minimum deviation isa) < 41° b) equal to 41° c) > 41° d) °≥ 41

37. A prism has a refractive angle of 60°. When placed in the position of minimum deviation, it produces a deviation of 30°. Then the angle ofincidences isa) 30° b) 45° c) 15° d) 60°.

38. A thin prism P1 with angle 4° and made from glass of refractive index 1.54 is combined with another prism P2 made from glass of refractiveindex 1.72 to produce dispersion without deviation. The angle of prism P2 is

a) 5.33° b) 4° c) 3° d) 2.6°39. In a simple microscope, if the final image is located at infinity then its magnifying power is

a) 25 / f b) 25 / D c) f / 25 d) { 1 + ( 25 / f )}

40. In a simple microscope, if the final image is located at 25 cm from the eye placed closed to the lens, then magnifying power isa) 25 / f b) { 1 + ( 25 / f )} c) f / 25 d) {( f / 25 ) + 1}

41. Magnifying power of an astronomical telescope for normal vision with usual notation is

a) − f f e0 / b) − ×f f e0 c) − f fe / 0 d) − +f fe0

42. The length of an astronomical telescope for normal vision is

a) f f e0 × b) f f e0 / c) f f e0 + d) f f e0 −

43. The magnifying power of a telescope is 9. When it is adjusted for parallel rays, the distance between the objective and the eyepiece is foundto be 20 cm. The focal length of lenses area) 18 cm, 2 cm b) 11 cm, 9 cm c) 10 cm, 10 cm d) 15 cm, 5 cm

44. If an astronomical telescope has objective and eyepiece of focal lengths 200 cm and 4 cm respectively, then the magnifying power of thetelescope for normal vision is

a) 42 b) 50 c) 58 d) 204

Answers

1. a 2. a 3. d 4. c 5. b 6. c7. d 8. b 9. a 10. a 11. b 12. b13. c 14. b 15. c 16. b 17. c 18. d19. c 20. b 21. d 22. b 23. a 24. b25. c 26. b 27. b 28. d 29. c 30. d31. a 32. b 33. b 34. a 35. b 36. a37. b 38. c 39. a 40. b 41. a 42. c43. a 44. b

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