Physics-DPP-2-Ray Optics

Daily Practice Problems No-2 PHYSICS Topic: RAY OPTICS Date: 1. A tank contains a transparent liquid to a height d ,of refractive index n the bottom of which is made of a mirror as shown. An object O lies at a height d above the mirror. A person P vertically above the object sees O and its image in the mirror and finds the apparent separation to be 2d (a) 2nd (b) n - 1 2d (c) n (d) d (1+ n) n 2. Light travels through a glass plate of thickness t having refractive index µ. If c is the velocity of light in vacuum, the time taken by the light to travel this thickness of glass is (a) t μc (b) t μ2c (c) μt c (d) μ2t c 3. When a ray is refracted from one medium to another, the wavelength changes from 6000Å to 4000Å. The critical angle for the interface will be –1 æç2ö÷ sin–1 æç 2 ö÷ –1 æç2ö÷ –1 æç 2 ö÷ (a) cos çè3ø÷ (b) çèç 3 ø÷ (c) sin çè3ø÷ (d) cos çèç 3 ø÷ 4. The plane faces of two identical plano convex lenses, each with focal length f are pressed against each other using an optical glue to form a usual lens. The distance from the optical centre at which an object must be placed to obtain the image same as the size of object is (a) f 4 (b) f 2 (c) f (d) 2f 5. An air bubble inside a glass slab appears to be 6 cm deep when viewed from one side and 4 cm deep when viewed from the other side. Assuming μ glass = 3 2 , the thickness of slab is (a) 10 cm (b) 20/3 cm (c) 15 cm (d) 20 cm 6. Two thin lenses, when in contact, produce a combination of power + 10D. When they are 0.25 m apart, the power reduces to + 6D. The focal lengths of the lenses (in m) are (a) 0.125 and 0.5 (b) 0.125 and 0.125 (c) 0.5 and 0.75 (d) 0.125 and 0.75 7. A concave lens of glass, refractive index 1.5, has both surfaces of same radius of curvature R. On immersion in a medium of refractive index 1.75, it will behaves as a (a) convergent lens of focal length 3.5 R (b) convergent lens of focal length 3.0 R (c) divergent lens of focal length 3.5 R (d) divergent lens of focal length 3.0 R 8. A parallel beam of light incident on a concave lens of focal length 10 cm emerges as a parallel beam from a convex lens placed coaxially, the separation between the lenses being 10 cm. The focal length of the convex lens in cm is (a) 10 (b) 20 (c) 15 (d) 30 9. A plano convex lens has a thickness of 4 cm. When placed on a horizontal table with curved surface in contact with it, the apparent depth of the bottom most point of the lens is found to be 3 cm. If the lens is inverted such that the plane face is in contact with the table, the apparent depth of the centre of plane face is found to be 25 cm . The focal length of the lens is 8 (a) 50 cm (b) 75 cm (c) 100 cm (d) 150 cm 10. A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screen (a) half the image will disappear (b) complete image will be formed (c) intensity of the image will increase (d) intensity of the image will decrease

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