OPTICS-06- SUBJECTIVE UNSOLVED (C.B.S.E.) LEVEL - I

UNSOLVED SUBJECTIVE (C.B.S.E.) LEVEL - I (REVIEW YOUR CONCEPTS) 1. An object is placed at (i) 10 cm (ii) 5 cm in front of a concave mirror of radius of curvature 15 cm. Calculate the position, nature and magnification of the image in each case. 2. A small candle 2.5 cm in size is placed at a distance of 27 cm in front of a concave mirror of radius of curvature 36 cm. At what distance from the mirror should a screen the placed in order to receive a sharp image ? Describe the nature and size of the image. If the candle is moved closer to the mirror, how would the screen have to be moved ? 3. A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Find the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror. 4. A square wire of side 3.0 cm is place 25 cm away from a concave mirror of focal length 10 cm. What is the area enclosed by the image of the wire ? Given : the centre of the wire is on the axis of the mirror, with its two sides normal to the axis. 5. A small pin fixed on a table top is viewed from above from a distance of 50 cm. By what distance would the pin appear to be raised if it is viewed from the same point through a 15 cm thick glass slab held parallel to the table ? Refractive index of glass = 1.5. Does the answer depend on the location of the slab ? 6. A ray of light enters the side of water-filled glass aquarium making an angle of 30º with a normal to the aquarium face. Calculate the angle made by the ray with normal within the galss and within the water. (Given : 0  1, ag  1.5, aw  1.33 .) 7. The bottom of a container is a 4.0 cm thick glass (  1.5) slab. The container contains two immis- cible liquids A and B of depths 6.0 cm and 8.0 cm respectively. What is the apparent position of a scratch on the outer surface of the bottom of the glass slab when viewed through the container ? Refractive indices of A and B are 1.4 and 1.3 respectively. 8. A small bulb is placed at the bottom of a tank containing water to a depth of 80 cm, What is the area of the surface of water through which light from the bulb can emerge out ? Refractive index of water is . [Consider the bulb to be a point source of light.] 9. At what angle should a ray of light be incident on the face of a prism of refracting angle 60º so that it just suffers total internal reflection at the other face ? The refractive index of the material of the prism is (sin15  14) . 10. You are given a double-convex lens made of crown glass with each surface of radius of curvature 15 cm. A flint glass is grafted on to one of the surfaces of this lens. What is the radius of curvature of the second surface of the flint glass lens for the combination to be an ‘achromatic doublet’ for blue and red light. For flint glass, b  1.660, r  1.644 . For crown glass, b  1.520, r  1.509 . 11. Light of wavelength 5000 Å falls on a plane reflecting surface. What are the wavelength and fre- quency of the reflected light ? For what angle of incidence is the reflected ray normal to the incident ray ? 12. Monochromatic light of wavelength 600 nm is incident from air on a glass surface. What are the wavelength, frequency and speed of the refracted light ? 13. In a Young’s double-slit experiment, the slits are separated by 0.28 mm and the screen is placed 1.4 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 1.2 cm. Determine the wavelength of light used in the experiment. 14. Monochromatic light of wavelength 589 mn is incident from air on a water surface. What are the wavelength, frequency and speed of (a) reflected, and (b) refracted light ? Refractive index of water is 1.33. 15. What is teh effect on the interference fringes in a Young’s double-slit experiment due to each of the following operations : (a) The screen is moved away from the plane of the slits; (b) The (monochromatic) source is replaced by another (monochromatic) source of shorter wavelength; (c) The separation between the two slits is increased; (d) The source slit is moved closer to the double-slit plane; (e) The width of the source slit is increased; (f) The widths of two slits are increased; (g) The monochromatic source is replaced by source of white light ? (In each operation, take all parameters, other than the one specified, to remain unchanged).

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