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9.RAY OPTICS AND OPTICAL INSTRUMENTS Single Correct Answer Type 1. A dentist has a small mirror of focal length 16 mm. He views the cavity in the tooth of a patient by holding the mirror at a distance of 8 mm from the cavity. The magnification is a) 1 b) 1.5 c) 2 d) 3 2. In an eye-piece, field lens and eye lens have focal lengths 7. 5 cmand 7. 3 cm. To eliminate spherical aberration, distance between them would be a) 0. 2 cm b) 0. 4 cm c) 0. 1 cm d) 0. 5 cm 3. When sunlight is scattered by atmospheric atoms and molecules, the amount of scattering of light of wavelength 440 nm is A. The amount of scattering for the light of wavelength 660 nm is approximately a) 4 9 A b) 2. 25 A c) 1. 5 A d) A 5 4. A double convex lens, lens made of a material of refractive index μ , is placed inside two liquids or 1 refractive indicesμ and , as shown. . A wide, parallel beam of light is incident on the lens 2 μ 3 μ 2 > μ 1 > μ 3 from the left. The lens will give rise to a) A single convergent beam b) Two different convergent beams c) Two different divergent beams d) A convergent and a divergent beam 5. A convex lens of focal length 30 cm produces 5 times magnified real image of an object. What is the object distance? a) 36 cm b) 25 cm c) 30 cm d) 150 cm 6. Light travels in two media A and B with speeds 1. 8×10 and respectively. Then the 8 ms −1 2. 4×10 8 ms −1 critical angle between them is a) 2 ( 3 ) b) 3 ( 4 ) c) 2 ( 3 ) d) 3 ( 4 ) 7. We combined a convex lens of focal length f and concave lens of focal lengths and their combined focal 1 f 2 length was F. The combination of these lenses will behave like a concave lens, if a) f 1 > f 2 b) f 1 < f 2 c) f 1 = f 2 d) f 1 ≤ f 2 8. A biconvex lens form a real image of an object placed perpendicular to its principal axis. Suppose the radii of curvature of the lens tend to infinity. Then the image would a) Disappear b) Remain as real image still c) Be virtual and of the same size as the object d) Suffer from aberrations 9. A divergent lens will produce Page| 1

A: Line spectra is due to atoms in gaseous state B: Band spectra is due to molecules a) Both A and B are false b) A is true and B is false c) A is false and B is true d) Both A and B are true 22. A person suffering from ‘presbyopia’ (myopia and hyper metropia both defects) should use a) A concave lens b) A convex lens c) A bifocal lens whose lower portion is convex d) A bifocal lens whose upper portion is convex 23. A man having height 6 m, observes image of 2 m height erect, then mirror used is a) Concave b) Convex c) Plane d) None of the above 24. An object is viewed through a compound microscope and appears in focus when it is 5 mm away from the objective lens. When a sheet of transparent material 3 mm thick is placed between the objective and the microscope, the objective lens has to be moved 1 mm to bring the object back into the focus. The refractive index of the transparent material is a) 1. 5 b) 1. 6 c) 1. 8 d) 2. 0 25. The Cauchy’s dispersion formula is a) n = A + Bλ −2 + Cλ −4 b) n = A + Bλ 2 + Cλ −4 c) n = A + Bλ −2 + Cλ 4 d) n = A + Bλ 2 + Cλ 4 26. A light ray is incident upon a prism in minimum deviation position and suffers a deviation of 34°. If the shaded half of the prism is knocked off, the ray will a) Suffer a deviation of 34° b) Suffer a deviation of 68° c) Suffer a deviation of 17° d) Not come out of the prism 27. The impact of an image on the retina remains for a) 0. 1 s b) 0. 5 s c) 10 s d) 15 s 28. An object is placed at a distance of 10cm from a convex lens of power 5D. Find the position of the image a) − 20 cm b) 30 cm c) 20 cm d) − 30 cm 29. If eye is kept at a depth h inside water of refractive index and viewed outside, then the diameter of the circle through which the outer objects become visible, will be a) h μ 2−1 b) h μ 2+1 c) 2h μ 2−1 d) h μ 2 30. Magnification at least distance of distinct vision of a simple microscope having its focal length 5 cm is Page| 3
a) 2 b) 4 c) 5 d) 6 31. Find the luminous intensity of the sun if it produces the same illuminance on the earth as produced by a bulb of 10000 candela at a distance 0. 3 m. The distance between the sun and the earth is 1. 5×10 11 m a) 25×10 22 cd b) 25×10 18 cd c) 25×10 26 cd d) 25×10 36 cd 32. Two immiscible liquids of refractive indices 1.5 and are filled in glass jar each of length 6 cm. A light of 4 3 source S is at the bottom of the jar, the apparent depth of light source will be a) 12.5 cm b) 17 cm c) 12 cm d) 8.5 cm 33. A parallel beam of white light falls on a convex lens. Images of blue, yellow and red light are formed on other side of the lens at a distance of 0. 20 m, 0. 205 m and 0. 214 m respectively. The dispersive power of the material of the lens will be a) 619/1000 b) 9/200 c) 14/205 d) 5/214 34. A ray of light passes an equilateral prism such that an angle of incidence is equal to the angle of emergence and the latter is equal to th the angle of prism. The angle of deviation is 3 4 a) 45° b) 39° c) 20° d) 30° 35. Two lenses having f has combination to make no dispersion. Find the ratio of dispersive power 1 : f 2 = 2 : 3 of glasses used a) 2 : 3 b) 3 : 2 c) 4 : 9 d) 9 : 4 36. A ray of light strikes a transparent rectangular slab (of refractive index 2) at an angle of incidence of 45°. The angle between the reflected and refracted rays is a) 75° b) 90° c) 105° d) 120° 37. What will be the colour of sky as seen from the earth, if there were no atmosphere a) Black b) Blue c) Orange d) Red 38. A convex lens of focal length forms a real, inverted image twice in size of the object. The distance of 1 3 m the object form the lens is a) 0.5 m b) 0.166 m c) 0.33 m d) 1 m 39. To get three images of a single object, one should have two plane mirrors at an angel of a) 60° b) 90° c) 120° d) 30° 40. Chromatic aberration of lens can be corrected by a) Reducing its aperature b) Proper polishing of its two surfaces c) Suitably combining it with another lens Page| 4