NK B . C O . I N OPTICS SECTION 1 QUESTIONS 1. A diverging beam of light falls on a plane mirror. The image formed by the mirror is a) real, erect b) virtual , inverted c) virtual, erect d) real, inverted 2. In a pond water is 10 m deep. A candle flame is held 15 m above the surface of water. If the refrac- tive index of water is 4/3, the image of the candle flame is formed at a) 15 m deep b) (45/4)m deep c) 10 m deep d) (30/4)m deep 3. Which of the following colours will have minimum critical angle when light passes from glass to air ? a) green b) blue c) yellow d) orange 4. *A ray of light is incident at an angle 45 0 in an equilateral prism of refractive index √2. The ray a) will totally reflect from the second face. b) will just graze the second surface. c) will run parallel to the incident ray. d) will undergo minimum deviation. 5. Light of wavelength λ and frequency f is incident from air to glass of refractive index µ . Inside glass the frequency and the wavelength of the light are a) f, µ λ b) µ f, µ λ c) f, λ/µ d) µ f, λ/µ 6. Two convex lenses of equal focal length f are kept at a distance coaxially. A parallel beam of light in- cident on the first lens emerges from the second lens as a parallel beam. The distance between the lenses is a) f b) 2f c) f/2 d) f/4 7. Imagine a hypothetical convex lens which can pass all the electromagnetic radiations through it. For which of the following radiations will the lens have maximum focal length? a) X-rays b) γ rays c) micro waves d) infra red rays 8. If a is the distance of an object from the focus of a concave mirror and b is the distance of its real im- age from the focus, the graph between a and b will be a) a straight line of positive slope b) a rectangular hyperbola c) a straight line with negative slope d) a parabola 9. A thin rod of length f/3 is placed along the optical axis of a concave mirror of focal length f such that its image which is real and elongated, just touches the rod. Its magnification is a) 3/2 b) 5/2 c) 1/2 d) 7/2 10. A concave mirror has a focal length of f cm. An object is placed such that it forms a two fold magni- fied real image. The distance between the object and the image will be ( in cm) a) f b) 1.5f c) 2f d) 2.5f 11. Two plane mirrors are inclined to each other at a certain angle. A ray of light first incident on one of them at an angle of 10 0 with the mirror retraces its path after five reflections. The angle between the mirror is a) 12 o b) 22 o c) 30 o d) 20 o 12. If represents the refractive index of the second medium with respect to the first medium, then will be equal to 21 µ 21 µ 32 µ 43 µ a) µ 41 b) µ 31 c) µ 14 d) µ 13 13. The intensity of light at a distance r from the axis of long cylindrical source is proportional to a) 1/r 2 b) 1/r c) 1/r 1/2 d) 1/r 3 14. A ray of light incident on an equilateral prism of refractive index 1.41 suffers minimum deviation. The angle of incidence on the first face is a) 60 o b) 30 o c) 40 o d) 45 o 15. A ray of light is incident on two plane mirrors inclined at an angle deviates through 240 o . The number of images of an object formed by the mirrors is equal to a) 3 b) 2 c) 5 d) 6 N K B . C O . I N Physics for IIT-JEE Screening Test 2 16. A fish is at a depth of 4 m from the water surface. A bird is at a height 3 m vertically above from the water surface. The distance at which the fish sees the bird is a) 7 m b) 9 m c) 8 m d) 10 m 17. A fish under water at a depth h sees the outside world within a cone of radius r at water surface. If µ is refractive index of water, the value of r here is 1 h ) d 1 h ) c 1 h ) b 1 h ) a 2 2 − µ − µ − µ − µ 18. A plano-convex lens of focal length f and radius of curvature R is silvered on the plane surface as shown in the adjacent figure The focal length of this will be a) f b) f/2 c) R d) R/2 19. The above plano-convex lens is silvered on the convex surface, as shown in the adjacent figure, so that it becomes a concave mirror. The focal length of this concave mirror will be a) R/2 b) R c) (R/2µ) d) 2R/µ 20. A ray of light passes through three media of refractive indices as shown in the adjacent figure. Then a) µ 1 =µ 2 , µ 3 >µ 2 b) µ 1 =µ 2 , µ 3 <µ 2 c) µ 1 =µ 2 =µ 3 d) µ 1 <µ 2 , µ 2 =µ 3 21. A plano–convex lens fits exactly with a plano-concave lens as shown in the adjacent figure. Their refractive indices and focal lengths are shown in the figure. The focal length of the combi- nation is 1 2 1 2 1 2 R ) d R ) c ) ( R 2 ) b ) ( 2 R ) a µ − µ µ − µ µ − µ 22. Light energy falls at a rate E Wm -2 on a perfectly reflecting plane mirror. The pressure exerted by the light on the mirror is (c speed of light) a) E/c b) 2E/c c) E/3600 c d) E/7200 c 23. A ray of light is incident at an angle 45 o into a medium of µ=√2 . A part of light is reflected and a part refracted. The angle between reflected and refracted rays in degrees will be a) 45 b) 75 c) 90 d) 105 24. An object is kept symmetrically between two plane mirrors inclined at an angle 90 o . The images formed by the mirror will lie in a) a circle b) a parabola c) a straight line d) an irregular curve 25. A source of light is kept in an isotropic medium. If the amplitude of wave reaching a point is plotted with distance from the source to the point, the graph will be a) a straight line b) an inverse square law graph c) a parabola d) rectangular hyperbola 26. A lamp is suspended vertically above a table at a height. When the height of suspension is reduced by 2%, the intensity at the centre of the table a) increases by 4% b) increases by 3% c) increases by 2% d) increases by 8% 27. Two lamps A and B are placed at a distance 2 m and 3 m from a screen respectively. The intensity of illumination on the screen due to the two lamps are equal. If P A and P B are the powers of two lamps, then P A /P B = a) 2/3 b) 4/9 c) 3/2 d) 9/4 28. The refractive index of a prism depends on a) angle of the prism A b) angle of minimum deviation D c) both A and D d) neither A nor D N K B . C O . I N Optics 3 Solve the following two problems within a maximum time of 2 minute. Use only one equation. 29. In a displacement method the distance between object and the screen is 90 cm. The focal length of the lens is 20 cm. What is the distance through which lens is displaced between magnified and dimin- ished image ? 30. In a displacement method the lens is displaced through a distance 45 cm. The magnification of one of the images =4. What is the focal length of the lens? 31. Young’s experiment is performed with white light, which of the following colours will have minimum band width ? a) green b) yellow c) blue d) red 32. If Young’s experiment were performed so that interfering beams travel in water. The ratio of width of band in air to that in water i.e. β(air) / β(water) = a) 1 b) 1/2 c) 3/4 d) 4/3 33. Two light beams have same wave vector k. One travels through a distance L 1 in a medium of refrac- tive index µ 1 and the other L 2 in a medium of refractive index µ 2. On emerging their phase difference will be a) k (µ 1 L 1 -µ 2 L 2 ) b) k(µ 1 L 2 -µ 2 L 1 ) c) (µ 1 L 1 -µ 2 L 2 )/k d) (µ 1 L 2 -µ 2 L 1 )/k 34. If one of the slits is twice as wide as the other in Young’s experiment, the ratio of intensity of bright band to dark band will be a) 4:1 b) 2:1 c) 3:1 d) 9:1 35. *.Which of the following cannot produce interference? a) Two narrow sources of blue light and red light b) One real narrow source and one narrow virtual source of same colour c) Two virtual monochromatic sources d) Two different parts of the same source 36. *If the width of both the coherent slits in Young’s experiment is progressively increased a) the width of bands will increase b) the width of bands will decrease c) the contrast between dark and bright bands will decrease d) the bands will disappear after some time 37. The relation between critical angle 'C' and angle of polarisation of a medium 'i' is a) i =tan -1 (cosec C) b) i =cot -1 (cosec C) c) i =sin -1 (tan C ) d) i =tan -1 (sin C) 38. A laser beam of wave length λ passing through a slit of width ‘a’ is sent to moon. The linear spread of the beam when it reaches to moon is a) Da/λ b) Dλ/a c) Da/2λ d) Dλ/2a 39. When the laser beam given in previous question reaches moon, the area to which it spreads is equal to a) D 2 a/λ b) D 2 λ 2 /a 2 c) ( Da/2λ) 2 d) Dλ 2 /a 2 40. Which of the following colours will have minimum polarising angle in a given medium? a) violet b) blue c) green d) indigo 41. If D 10 2 =x, D 15 2 =y, D 20 2 =z, where D 10 , D 15 and D 20 are the diameters of 10 th , 15 th and 20 th dark ring of a Newton’s ring system, then a) y-x =2(z-y) b) 2(y-x) =z-y c) z-x =2y d) y-x =z-y 42. For a certain experiment it is required to diffract H α line of Balmer series. The wave length of this line is about 660 nm. Which of the following grating would be most suitable for this? a) A grating having 10 6 lines /m b) A grating having 10 4 lines/m c) A grating having 6000 lines/m d) A grating having 3x10 8 lines/m 43. *. Which of the following statements are correct about optic axis? a) It is a line b) It is a direction c) The crystal is symmetric about it d) The speed of O and E rays will be same along it. 44. If the acute angle of a biprism is increased, the width of the fringes produced by it a) decreases b) increases c) remains the same d) cannot be said from the data N K B . C O . I N Physics for IIT-JEE Screening Test 4 45. The polarising angle of ordinary glass is equal 57 o . If this glass is immersed in water, the polarising angle will be a) more than 57 0 b) equal to 57 0 c) less than 57 0 d) exactly equal to 45 0 46. In the earth’s atmosphere the ratio of amplitude of blue light scattered to that of red light , if their wave lengths are 400 nm and 600 nm respectively, is a) 9/4 b) 4/9 c) 81/16 d) 16/81 47. In the figure below unpolarised light of intensity I 0 =64 W/m 2 is incident on the first polaroid N 1 . The intensity of light coming from the second polaroid N 2 is I 2, =2 W/m 2 . The angle between the axis of N 1 and that of N 2 is equal to a) 30 o b) 60 0 c) cos -1 (1/4) d) cos -1 (1/8) 48. Suppose the polaroid N 2 in the previous question is rotated keeping N 1 fixed. During one rotation, an observer will see a) a maximum and a minimum b) four maxima and four minima c) two maxima and two minima d) light of varying intensity but no minimum and maximum 49. Laser beam can be used to standardise a) distance b) time c) angle d) temperature 50. A laser beam of frequency 3x10 14 Hz passes through an aperture of diameter 1 mm. The angular spread of the beam in radian is equal to a) 10 -2 b) 10 -4 c) 5x10 -3 d) 10 -3 51. Which of the following statement(s) are true for photons ? a) Their rest mass is zero b) Their rest mass is infinite c) They cannot produce interference d) They travel with a speed equal to that of light waves 52. If the width of source slit in Young’s experiment is increased, a) the fringe width will increase b) the fringe width will decrease c) the bright bands will become more bright d) the visibility of the system will become less 53. A ray of light of intensity I is incident on a parallel glass-slab at a point A as shown in adjacent figure. It undergoes partial reflection and refraction. At each reflection 25% of in- cident energy is reflected. The rays AB and A′B′ undergo interference. The ratio I max /I min is: a) 4:1 b) 8:1 c) 7:1 d) 49:1 54. The position of the direct image obtained at O, when a monochromatic beam of light is passed through a plane transmission grating at normal incidence is shown in the adjacent figure. The diffracted im- ages A,B and C correspond to the first, second and third order diffraction. When the source is replaced by another source of shorter wavelength a) all the four images shift in the direction C to O b) the images C,B and A will shift towards O c) all the four images shift in the direction O to C d) the images C, B and A will shift away from O N K B . C O . I N Optics 5 55. If the coherent slits in Young’s experiment are narrowed so that their width becomes comparable with the wavelength of light, a) the fringes will become broad b) the fringes will become narrower c) the fringes will become unequally spaced d) the fringes will disappear and uniform illumination will set in 56. A mixture of red light of λ =6000 A o and blue light of λ =4400 A o is incident normally on an air film. The minimum thickness of the film for which the reflected light will appear blue is a) 3x10 -7 m b) 6 x 10 -7 m c) 2.2 x 10 -7 m d) 4.4 x 10 -7 m 57. Which of the following gives maximum field of view ? a) plane mirror b) concave mirror c) convex mirror d) cylindrical mirror 58. A ray of light falls on a plane mirror at angle of incidence i. The deviation produced on the ray by the mirror is a) 2i b) (180-2i) c) (180 +2i) d) (360-2i) 59. When a convergent beam of light is incident on a plane mirror, the image formed is a) erect and real b) erect and virtual c) inverted and real d) inverted and virtual 60. When the moon is near horizon, it appears bigger due to a) refraction b) scattering of light c) diffraction d) all the three 61. How many images of himself does an observer see on the mirror surfaced two adjacent walls and the ceiling of a rectangular room? a) 3 b) 5 c) 6 d) 9 62. A glass slab is placed in the path of converging beam of light. The point of convergence of light a) moves towards the glass slab b) moves away from the glass slab c) remains at the same point d) undergoes a lateral shift 63. A plane glass slab is placed on the letters of the following colours. The letters of which colour is raised maximum ? a) red b) yellow c) green d) blue 64. A ray of light passes from vacuum into a medium at an angle of incidence twice the angle of refrac- tion. The angle of incidence is a) cos -1 (µ/2) b) 2 cos -1 (µ/2) d) 2 sin -1 (1/µ) d) 2 sin -1 (µ/2) 65. A light wave of frequency 5 x 10 14 Hz enters a medium of refractive index 1.5. In the medium the ve- locity of the light wave is a) 3 x 10 8 m/s b) 2 x 10 8 m/s c) (5/10 14 /1.5) m/s d) 1.5 x 5 x 10 14 m/s 66. A small plane mirror is rotating with a constant frequency of n rotations per second. With what linear velocity (in m/s) a spot of light reflected from the mirror moves along a spherical screen of radius of curvature R, if the mirror is at the centre of curvature of screen ? a) 2πnR b) 2nR c) 4nR d) 4πnR 67. When a source of light is 1 m away, a photosensitive meter gives a delfection of 8 divisions, if the source is moved 1m more, the deflection will be a) 8 divisions b) 4 divisions c) 2 divisions d) 9 divisions 68. The critical angle of a prism is 36 0 . The maximum angle of the prism for which an emergent ray is possible is a) 72 0 b) 54 0 c) 36 0 d) 16 0 69. A thin prism P 1 of angle 4 0 and ,made from glass of refractive index 1.54 is combined with another thin prism P 2 made from glass of refractive index 1.72 so that ray undergoes no deviation. The angle of prism P 2 is a) 5.33 0 b) 4 0 c) 3 0 d) 2.6 0 70. The distance between an object and a divergent lens is x times the focal length of the lens. The lateral magnification m produced by the lens will be a) x b) 1/x c) x+1 d) 1/x+1 71. The colour of light which travels with minium speed in glass is a) red b) yellow c) green d) blue N K B . C O . I N Physics for IIT-JEE Screening Test 6 72. A convex lens is placed between an object and screen which are at a fixed distance apart. For one po- sition of the lens the magnification of the image obtained on the screen is m 1 . When the lens is moved by a distance d, the magnification of the image obtained on the same screen is m 2 . The focal length of the lens is (m 1 >m 2 ) a) d/(m 1 -m 2 ) b) d/(m 1 +m 2 ) c) dm 1 /m 2 d) m 2 /m 1 73. In a displacement method using convex lens we obtain two images for separation of the lens d. One image is magnified as much as the other is diminished. If m is the magnification of one image, the fo- cal length of the lens is a) d/(m-1) b) md(m 2 -1) c) d/(m 2 -m) d) dm 2 /m 1 74. If the earth had no atmosphere, the duration of the day would have been a) longer b) the same c) shorter d) shorter or longer depending on the season 75. A short linear object of length b lies along the axis of a concave mirror of focal length f at a distance u from the pole of the mirror. The size of the image is approximately equal to a) b 2 / 1 f u f ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − b) 2 f u f b ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − c) 2 f f u b ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − d) ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − f f u b 76. Two convex lenses separated by a distance are brought into contact. The focal power of the combina- tion a) decreases b) increases c) remains the same d) cannot be said from the data 77. A transparent cube of 12 cm edge contains a small air bubble. Its apparent depth is 5 cm when viewed through one face and 3 cm when viewed through the opposite face. The refractive index of the mate- rial of the cube is a) 1.5 b) 12/7 c) 12/5 d) 5/3 78. A source of light located at a point A where AB =BC =1 m as shown in fig. The intensity of illumi- nation at B is P. The intensity of illumination at C is a) 0.36 P b) 0.5 P c) 0.7 P d) 0.44 P 79. A diver from inside water looks at an outside object whose natural colour is green. He sees the object as a) green b) red c) violet d) yellow 80. An ant is approaching a convex lens with a constant speed up to the first focus. The speed of the image of ant formed by the lens. a) remains the same b) increases uniformly c) first decreases and then increases d) first increases and then decreases 81. A thin lens of focal length f and aperture diameter d forms an image of intensity I. The central part of the aperture up to diameter d/2 is blocked by an opaque paper. The focal length and image intensity would respectively be a) f, I/4 b) f/2, I/2 c) 3f/4, I/2 d) f, I/2 82. Two thin lenses of focal lengths f 1 and f 2 are placed at a distance d between them. For power of the combination to be zero, the separation of the lenses must be a) f 1 +f 2 b) 2 f f 2 1 + c) 2 1 f f d) 2 1 f f 83. A blue cross illuminated by white light under white background is observed through a red filter. The observer will see a) a red cross on a black background b) a red cross on a blue background c) a black cross on a red background d) a black cross on a blue background 84. The angle of a prism is A and the angle of minimum deviation is 180-2A. the refractive index of the prism is a) sin (A/2) b) cos (A/2) c) tan (A/2) d) cot (A/2) 85. A glass prism has a refractive index of 1.5 and refracting angle of 90 0 . A ray of light is incident on it at an angle of incidence of 30 0 . The angle of emergence will be in degrees a) 60 b) 30 c) 45 d) the ray will not emerge N K B . C O . I N Optics 7 86. A ray of light is incident at an angle of 60 0 on one face of a prism of refracting angle 30 0 . The emer- gent ray makes an angle 30 0 with the incident ray. The refractive index of the prism is a) 1.41 b) 1.73 c) 1.5 d) 1.6 87. A ray of monochromatic light is incident on one face of a prism of angle 75 0 . It is incident on the second face at criti- cal angle. If µ =√2, the angle of incidence on the first face of the prism is (in degrees) a) 30 b) 45 c) 60 d) 90 88. A beam of light consisting of red, green blue colours is inci- dent on right angled prism normally on the face AB. The re- fractive indices of the prism for red, green and blue are 1.39, 1.44 and 1.47 respectively. The prism will a) separate red colour from blue and green b) separate part of blue colour from red and green c) separate all the three colours from one another d) not separate even partially any colour from the others 89. A prism of critical angle 42 0 is immersed in water of critical angle 49 0 . The critical angle of the prism inside water will be a) between 42 0 and 49 0 b) less than 42 0 c) greater than 49 0 d) equal to 49 0 90. The angle with horizontal at which an under-water swimmer will see the setting sun is a) 41 0 b) 32 0 c) 49 0 d) 60 0 91. A spherical air bubble in water will act as a) a convex lens b) a concave lens c) plane glass plate d) plano-concave lens 92. When a lens is moved towards the object from a distance 20 cm to 15 cm, the magnification of the image remains the same. The focal length of the lens is a) 16.8 cm b) 15.5 cm c) 18.2 cm d) 17.5 cm 93. Which of the following is an achromatic combination pair of a telescope objective? d 45° C A B a) Lenses of of power +3D and - 5D b) Lenses of f =40 cm and power –3 D c) Lenses of f =-50 cm and power +2D d) Lenses of f =+20 cm and power –4.5 D 94. A convex lens A of focal length 20 cm and a concave lens B of focal length 5 cm are kept along the same axis with a distance d be- tween them.. If a parallel beam of light fal- ling on a leaves B as a [parallel beam of light falling on A leaves B as a parallel beam, then d is equal to (in cm) a) 25 b) 22.5 c) 20 d) 15 95. A parallel beam of white light falls on a combination of a concave and a convex lens, both of the same material. Their focal lengths are 15 and 30 cam respectively for the mean wavelength in white light. On the other side of the lens system, one sees a) white pattern b) no pattern at all c) coloured pattern with violet at inner side d) coloured pattern with violet at outer side 96. Consider Fraunhofer diffraction pattern obtained with a single slit, illuminated at normal incidence. At the angular position of the first diffraction minimum, the phase difference (in radians) between the wavelets from the opposite edges of the slit is a) π b) 2π c) π/4 d) π/2 97. *A planet is observed by an astronomical refracting telescope having objective of focal length 16 m and eyepiece of focal length 2 cm. Then a) The distance between objective and eyepiece is 16.02 m b) The angular magnification of the planet is –800 c) The image of the planet is inverted d) The objective is larger than the eye-piece N K B . C O . I N Physics for IIT-JEE Screening Test 8 98. Interference fringes are formed with light of wavelength 400 nm in Young’s experiment with separa- tion of slit 1 mm and screen distance 1 m. The angular width of fringe (in radian) is a) 0.4 b) 0.04 c) 0.004 d) 0.0004 99. If Young’s experiment with one source of light and two slits be performed so that interfering beam traverse in water instead of air, a) the fringes will be less in number b) the fringes will be broader c) the fringes will be narrower d) no fringes will be obtained 100. In Young’s interference experiment with one source and two slits, one slit is covered with a cellophane sheet so that only half of the intensity is transmitted. Then a) no fringes will be obtained b) bright fringes will be brighter and dark fringes will be darker c) all fringes will be darker d) bright fringes will be less bright and dark fringes will be less dark 101. In a Young’s double slit experiment, the interference pattern is found to have an intensity ratio of 9 be- tween bright and dark fringes. This implies that a) the intensities at the screen due to the two slits are 5 units and 4 units respectively b) the intensities all the screen due to the two slits are 4 units and 1 unit respectively c) the amplitude ratio is 3/2 d) the amplitude ratio is 3 102. In Young’s double slit experiment the central fringe is white. What colour of fringe will you see near- est to the central fringe ? a) violet b) green c) red d) yellow 103. *White light is used to illuminate the two slits in a Young’s double slit experiment. The separation be- tween the slits is b and the screen is at a distance d ( >>b) from the slits. At a point on the screen di- rectly in front of one of the slits, certain wave lengths are missing. Some of these missing wavelengths are a) λ =b 2 /d b) λ =2b 2 /d c) λ =b 2 /3d d) λ =2b 2 /3d 104. In Young’s double slit experiment using light of wavelength λ, the intensity of one bright fringe is I units. The intensity of light at a point where the path difference is λ/4 is a) I/2 b) I/4 c) I/3 d) I/9 105. The polarising angle of diamond is 67 0 . The critical angle of diamond is nearest to a) 22 0 b) 34 0 c) 45 0 d) 60 0 106. A ray of light enters from a rarer medium to a denser medium at an angle of incidence i. The reflected and refracted rays make an angle of 90 0 with each other. The angles of reflection and refraction are r and r’ respectively. The critical angle of denser medium is a) sin -1 (tan r’) -1 b) sin -1 (tan r’1) -1 c) sin -1 (tan i) -1 d) tan -1 (sin i) 107. Two nicol prisms (polariser and analyser) have their axes an angle 30 0 in between. If I is the intensity of light falling on first nicol,. Then the intensity of emerging light from second nicol is a) (1/8) I b) (3/8)I c) (1/4)I d) (1/2)I 108. A point source of light is to be suspended above the centre of a circular table of radius R. In order to produce maximum illumination at the edge of the table, the height of the light source should be a) R b) b) 2 R c) R / 2 d) R/2 109. If a star emitting yellow light starts accelerating towards the earth, its colour as seen from earth will a) turn gradually red b) turn gradually yellow c) remain unchanged d) turn gradually blue 110. An astronomical telescope has large aperture to a) reduce spherical aberration b) have high resolution c) have low dispersion d) increase the span observation 111. The distance between virtual sources in a biprism of angle α and refractive index µ, if the source is placed at distance a from it, is a) 2 (µ-1) α b) (µ-1)α a/2 c) (µ-1) α d) 2(µ-1)α a 112. In Newton’s rings the radius of the first dark ring 2 mm. The radius of the third dark ring will be a) 3 mm b) 2 mm c) 1.7 mm d) 3.4 mm N K B . C O . I N Optics 9 113. If Young’s experiment could be performed with the following radiations, which of them will give bands of minimum width? a) red light b) radio waves c) violet light d) micro waves 114. Which of the following is inevitable for a Fraunhoffer diffraction experiment? a) White light source b) a colour filter c) a telescope d) a convex lens 115. Which of the following can be polarised ? a) α rays b) β rays c) γ rays d) all the three 116. Energies of photon of four different electromagnetic radiations are given below. Which energy value corresponds to a visible photon ? a) 1 eV b) 2.5 eV c) 5 eV d) 1000 eV 117. The first crucial experiment if in favour of wave theory was carried out by a) Huygens b) Foucault c) Newton d) Thomas Young 118. An interference pattern is observed by Young’s double slit experiment. If now the separation between coherent sources is halved and the distance of screen from coherent sources is doubled ; the now fringe width a) becomes double b) becomes one-fourth c) remains the same d) becomes four times 119. The two slits in Young’s double slit experiment are illuminated by two different parts of same sodium lamp. Then a) uniform illumination will be seen b) interference pattern with dark and bright fringes is observed c) interference pattern with circular yellow fringes is observed d) complete darkness will be seen 120. Young’s experiment is performed with while light. The wavelength of red light =660 nm. The wave- length of blue light =440 nm. The minimum order of the red light fringe which coincides with a blue light fringe is equal to a) 2 b) 3 c) 4 d) 5 121. In Young’s experiment monochromatic light is used to illuminate the slits A and B. Interference fringes are observed on a screen placed in front of the slits. Now if a thin glass plate is placed in the path of the beam coming from A, then a) the fringes will disappear b) the fringe width will increase c) there will be no change in the fringe width d) the fringes will shift 122. The wavelength of light plays no role in a) interference b) diffraction c) polarisation d) resolving power 123. The critical angle of a certain medium is sin -1 (3/5). The polarising angle of the medium is a) sin -1 (4/5) b) tan -1 (5/3) c) tan -1 (3/4) d) tan -1 (4/3) 124. Double refraction of light is shown by a) quartz and calcite only b) calcite only c) calcite and ice only d) calcite, ice and quartz 125. A diffraction grating has 5000 lines/cm. The maximum order visible with wavelength 6000A 0 is a) 2 b) 3 c) 4 d) 50 126. If a drop of water is introduced between the glass plate and a convex lens in a Newton’s ring system, the ring system a) contracts b) expands c) remains the same d) first expands, then contracts 127. A fly is sitting on the objective of a telescope pointed towards the moon. What effect is expected in a photograph of the moon taken through the telescope? a) the entire field of view will be blocked b) there will be image of the fly on the photograph c) there will be no effect at all d) there ill be reduction in the intensity of the image N K B . C O . I N Physics for IIT-JEE Screening Test 10 128. A lens is placed between a source of light and a wall. It forms images of area A 1 and A 2 on the wall for its two different positions. The area of the source of light is 1 2 1 2 2 1 2 1 2 1 )] A / 1 ( ) A / 1 [( ) d ] 2 / A A [( ) c 2 / ) A A ( ) b A A ) a − + + + 129. The diameter of the moon is 3.5 x 10 3 km and its distance from the earth is 3.8 x 10 5 km. It is seen by a telescope having the focal lengths of the objective and the eye piece 4 m and 10 cm respectively. The diameter of the image of moon would be approximately a) 2 0 b) 20 0 c) 40 0 d) 50 0 130. An eye piece consists of two lenses of focal lengths f 1 and f 2 . In order that the combination is achro- matic, the lenses are to be separated by a distance a) 2f 1 f 2 /f 1 +f 2 b) 2f 1 f 2 / f 1 – f 2 c) f 1 +f 2 /2 d) f 1 – f 2 131. A person can see clearly up to 3 m. What is the power of the lens he should use so that he can see upto 12 m ? a) +0.5 D b) -0.5 D c) +0.25 D d) -0.25 D 132. If the accelerating potential increases to 4 times in an electron microscope, its resolving power R would change to a) R/4 b) 4R c) 2R d) R/2 133. Which of the following is true for a quarter wave plate ? a) It is made of glass and produces a phase difference π/2 b) It is made of glass and produces a phase difference π/4 c) It is made of quartz and produces a phase difference π/2 d) It is made of quartz and produces a phase difference π/4 134. Which of the following can diffract sound waves from a tuning fork of the frequency 384 Hz? a) a sphere of diameter 10 m b) a sphere of diameter 1 m c) a sphere of diameter 1 cm d) a sphere of diameter 1 mm 135. The exposure time of a camera lens at the f/2.8 setting is 1/200 second. The correct time of exposure at f/5.6 setting is a) 0.02 sec b) 0.04 sec c) 0.20 sec d) 0.40 sec N K B . C O . I N Optics 11 SECTION 2: ANSWERS 1 c 2 a 3 b 4 d 5 b 6 b 7 b 8 b 9 a 10 b 11 d 12 a 13 b 14 d 15 c 16 c 17 c 18 b 19 c 20 a 21 d 22 b 23 d 24 a 25 d 26 a 27 b 28 d 29 30 cm 30 12 cm 31 c 32 d 33 a 34 d 35 a,d 36 c,d 37 a 38 b 39 b 40 c 41 d 42 a 43 b,c,d 44 a 45 c 46 a 47 c 48 c 49 a 50 d 51 a,d 52 d 53 d 54 b 55 c 56 a 57 c 58 b 59 a 60 a 61 6 62 b 63 d 64 b 65 b 66 d 67 c 68 a 69 c 70 d 71 d 72 a 73 b 74 c 75 d 76 b 77 a 78 a 79 c 80 c 81 a 82 a 83 c 84 d 85 d 86 b 87 b 88 a 89 c 90 a 91 b 92 d 93 d 94 d 95 d 96 b 97 a,b,c,d 98 d 99 c 100 d 101 b 102 a 103 a,c 104 a 105 a 106 c 107 b 108 c 109 d 110 b 111 d 112 d 113 c 114 d 115 c 116 b 117 b 118 d 119 a 120 a 121 d 122 c 123 b 124 d 125 b 126 a 127 d 128 a 129 b 130 c 131 d 132 c 133 c 134 b 135 a