COFEAINEREN SERENE ORENS E ALLEN 68 The focal length of a convex lens is 10 cm and its refractive index is 1 5 If the radius of curvature of one surface is 7 5 cm the radius of curvature of the second surface will be 1 7 5 cm 2 15 0 cm 3 75 cm 4 5 0 cm GO0068 69 A plano convex lens u 1 5 has radius of curvature 10 cm It is silvered on its plane surface Find focal length after silvering 1 10 cm 2 20 cm 3 15 cm 4 25 cm GO0069 70 A plano convex lens is made of refractive index 75 1 6 The radius of curvature of the curved surface is 60 cm The focal length of the lens is 1 50 cm 2 100 cm 3 200 cm 4 400 cm GO0070 71 If in a plano convex lens the radius of curvature of the convex surface is 10 cm and the focal length of the lens is 30 cm then the refractive index of the material of lens will be 1 1 5 2 1 66 3 1 33 4 3 GO0071 72 If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together what will be their resulting power 1 6 5 D 2 6 5 D 3 7 5 D 4 0 75 D 73 A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens Then its focal length will 1 Become zero 2 Become infinite 3 Become small but non zero 4 Remain unchanged GO0073 74 An equiconvex lens is cut into two halves along i XOX and ii YOY as shown in the figure Let f f f be the focal lengths of the complete lens of Pre Medical Physics 59 each half in case i and of each half in case ii respectively Choose the correct statement from the following 1 ff f 2f 2 f 2f f f 77 3 ff f f 4 f 2f f 2f G00074 An object and its real image are located at distances 25 cm and 40 cm respectively from the two principal focii of a convex lens The linear magnification of the image is near to 1 1 3 2 1 3 3 1 8 4 1 8 GO0075 CHROMATIC SPHERICAL ABERRATIONS 76 Lenses applied in achromatic combination having dispersive power in ratio of 5 3 if focal length of concave lens is 15 cm then focal length of other lens will be 1 9 cm 2 9 cm 3 12 cm 4 12 cm GO0076 If the magnitude of dispersive powers of two lenses are 0 024 and 0 036 Then their focal lengths will be for aberration free combination 1 30 cm 40 cm 3 10 cm 30 cm GO0077 GO0072 78 An achromatic convergent doublet of two lenses in contact has a power of 2D The convex lens has a power 5D What is the ratio of the dispersive powers of the convergent and divergent lenses 1 2 5 2 3 5 3 5 2 4 5 3 GO0078 2 30 cm 45 cm 4 20 cm 35 cm 79 The dispersive powers of the materials of the two lenses are in the ratio 4 3 If the achromatic combination of these two lenses in contact is a convex lens of focal length 60 cm then the focal lengths of the component lenses are 1 20 cm and 25 cm 2 20 cm and 25 cm 4 15 cm and 20 cm 3 15 cm and 40 cm GO0079