
question_answer1) The radius of curvature for a convex lens is 40 cm, for each surface. Its refractive index is 1.5. The focal length will be [MP PMT 1989]
A) 40 cm done
clear
B) 20 cm done
clear
C) 80 cm done
clear
D) 30 cm done
clear
View Solution play_arrow

question_answer2) A convex lens of focal length \[f\] is placed somewhere in between an object and a screen. The distance between the object and the screen is \[x\]. If the numerical value of the magnification produced by the lens is \[m,\], then the focal length of the lens is
A) \[\frac{mx}{{{(m+1)}^{2}}}\] done
clear
B) \[\frac{mx}{{{(m1)}^{2}}}\] done
clear
C) \[\frac{{{(m+1)}^{2}}}{m}x\] done
clear
D) \[\frac{{{(m1)}^{2}}}{m}x\] done
clear
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question_answer3) A thin lens focal length \[{{f}_{1}}\] and its aperture has diameter d. It forms an image of intensity I. Now the central part of the aperture upto diameter \[\frac{d}{2}\] is blocked by an opaque paper. The focal length and image intensity will change to [CPMT 1989; MP PET 1997; KCET 1998]
A) \[\frac{f}{2}\] and \[\frac{I}{2}\] done
clear
B) \[f\] and \[\frac{I}{4}\] done
clear
C) \[\frac{3f}{4}\] and \[\frac{I}{2}\] done
clear
D) \[f\] and \[\frac{3I}{4}\] done
clear
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question_answer4) A lens of power + 2 diopters is placed in contact with a lens of power  1 diopter. The combination will behave like
A) A convergent lens of focal length 50 cm done
clear
B) A divergent lens of focal length 100 cm done
clear
C) A convergent lens of focal length 100 cm done
clear
D) A convergent lens of focal length 200 cm done
clear
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question_answer5) A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of combination is [IITJEE 1982; AFMC 1997; CBSE PMT 2000; RPMT 2003]
A)  1.5 D done
clear
B)  6.5 D done
clear
C) + 6.5 D done
clear
D) + 6.67 D done
clear
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question_answer6) Two lenses are placed in contact with each other and the focal length of combination is 80 cm. If the focal length of one is 20 cm, then the power of the other will be [NCERT 1981]
A) 1.66 D done
clear
B) 4.00 D done
clear
C) 1.00 D done
clear
D)  3.75 D done
clear
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question_answer7) Two similar planoconvex lenses are combined together in three different ways as shown in the adjoining figure. The ratio of the focal lengths in three cases will be
A) 2 : 2 : 1 done
clear
B) 1 : 1 : 1 done
clear
C) 1 : 2 : 2 done
clear
D) 2 : 1 : 1 done
clear
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question_answer8) Two lenses of power +12 and  2 diopters are placed in contact. What will the focal length of combination [MP PET 1990; MNR 1987; MH CET (Med.) 2001; UPSEAT 2000; Pb. PMT 2003]
A) 10 cm done
clear
B) 12.5 cm done
clear
C) 16.6 cm done
clear
D) 8.33 cm done
clear
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question_answer9) A concave and convex lens have the same focal length of 20 cm and are put into contact to form a lens combination. The combination is used to view an object of 5 cm length kept at 20 cm from the lens combination. As compared to the object, the image will be [CPMT 1986; RPMT 1997]
A) Magnified and inverted done
clear
B) Reduced and erect done
clear
C) Of the same size as the object and erect done
clear
D) Of the same size as the object but inverted done
clear
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question_answer10) If in a planoconvex 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 [CPMT 1986; MNR 1988; MP PMT 2002; UPSEAT 2000]
A) 1.5 done
clear
B) 1.66 done
clear
C) 1.33 done
clear
D) 3 done
clear
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question_answer11) The slit of a collimator is illuminated by a source as shown in the adjoining figures. The distance between the slit S and the collimating lens L is equal to the focal length of the lens. The correct direction of the emergent beam will be as shown in figure [CPMT 1986]
A) 1 done
clear
B) 3 done
clear
C) 2 done
clear
D) None of the figures done
clear
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question_answer12) A converging lens is used to form an image on a screen. When upper half of the lens is covered by an opaque screen [IITJEE 1986; SCRA 1994; MP PET 1996; MP PMT 2004; BHU 1998, 05]
A) Half the image will disappear done
clear
B) Complete image will be formed of same intensity done
clear
C) Half image will be formed of same intensity done
clear
D) Complete image will be formed of decreased intensity done
clear
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question_answer13) A thin convex lens of focal length 10 cm is placed in contact with a concave lens of same material and of same focal length. The focal length of combination will be [CPMT 1972; 1988]
A) Zero done
clear
B) Infinity done
clear
C) 10 cm done
clear
D) 20 cm done
clear
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question_answer14) A convex lens of focal length 84 cm is in contact with a concave lens of focal length 12 cm. The power of combination (in diopters) is [MP PET 1991]
A) 25/24 done
clear
B) 25/18 done
clear
C)  50/7 done
clear
D) + 50/7 done
clear
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question_answer15) A convex lens makes a real image 4 cm long on a screen. When the lens is shifted to a new position without disturbing the object, we again get a real image on the screen which is 16 cm tall. The length of the object must be [MP PET 1991]
A) 1/4 cm done
clear
B) 8 cm done
clear
C) 12 cm done
clear
D) 20 cm done
clear
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question_answer16) A glass convex lens \[({{\mu }_{g}}=1.5)\] has a focal length of \[8\,cm\] when placed in air. What would be the focal length of the lens when it is immersed in water ( \[{{\mu }_{w}}=1.33\]) [BHU 1994; MP PMT 1996]
A) 2 m done
clear
B) 4 cm done
clear
C) 16 cm done
clear
D) 32 cm done
clear
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question_answer17) The ray diagram could be correct [CPMT 1988]
A) If \[{{n}_{1}}={{n}_{2}}={{n}_{g}}\] done
clear
B) If \[{{n}_{1}}={{n}_{2}}\] and \[{{n}_{1}}<{{n}_{g}}\] done
clear
C) If \[{{n}_{1}}={{n}_{2}}\] and \[{{n}_{1}}>{{n}_{g}}\] done
clear
D) Under no circumstances done
clear
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question_answer18) A thin convex lens of refractive index 1.5 has a focal length of 15 cm in air. When the lens is placed in liquid of refractive index 4/3 , its focal length will be [CPMT 1974, 77; MP PMT 1992]
A) 15 cm done
clear
B) 10 cm done
clear
C) 30 cm done
clear
D) 60 cm done
clear
View Solution play_arrow

question_answer19) A glass lens is placed in a medium in which it is found to behave like a glass plate. Refractive index of the medium will be [CPMT 1981, 84, 85]
A) Greater than the refractive index of glass done
clear
B) Smaller than the refractive index of glass done
clear
C) Equal to refractive index of glass done
clear
D) No case will be possible from above done
clear
View Solution play_arrow

question_answer20) If \[{{I}_{1}}\] and \[{{I}_{2}}\] be the size of the images respectively for the two positions of lens in the displacement method, then the size of the object is given by [CPMT 1988]
A) \[{{I}_{1}}/{{I}_{2}}\] done
clear
B) \[{{I}_{1}}\times {{I}_{2}}\] done
clear
C) \[\sqrt{{{I}_{1}}\times {{I}_{2}}}\] done
clear
D) \[\sqrt{{{I}_{1}}/{{I}_{2}}}\] done
clear
View Solution play_arrow

question_answer21) A convex lens of crown glass (\[n\]=1.525) will behave as a divergent lens if immersed in [CPMT 1984]
A) Water (n =1.33) done
clear
B) In a medium of n = 1.525 done
clear
C) Carbon disulphide n =1.66 done
clear
D) It cannot act as a divergent lens done
clear
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question_answer22) A divergent lens will produce [CPMT 1984]
A) Always a virtual image done
clear
B) Always real image done
clear
C) Sometimes real and sometimes virtual done
clear
D) None of the above done
clear
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question_answer23) The minimum distance between an object and its real image formed by a convex lens is [CPMT 1973; JIPMER 1997]
A) 1.5 \[f\] done
clear
B) 2 \[f\] done
clear
C) 2.5 \[f\] done
clear
D) 4 \[f\] done
clear
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question_answer24) An object is placed at a distance of 20 cm from a convex lens of focal length 10 cm. The image is formed on the other side of the lens at a distance [CPMT 1971; RPET 2003]
A) 20 cm done
clear
B) 10 cm done
clear
C) 40 cm done
clear
D) 30 cm done
clear
View Solution play_arrow

question_answer25) Two thin lenses, one of focal length + 60 cm and the other of focal length 20 cm are put in contact. The combined focal length is [CPMT 1973, 89; BVP 2003]
A) + 15 cm done
clear
B) 15 cm done
clear
C) + 30 cm done
clear
D) 30 cm done
clear
View Solution play_arrow

question_answer26) A double convex lens of focal length 20 cm is made of glass of refractive index 3 / 2. When placed completely in water \[{{(}_{a}}{{\mu }_{w}}=4/3)\], its focal length will be [CBSE PMT 1990; MP PMT/PET 1998]
A) 80 cm done
clear
B) 15 cm done
clear
C) 17.7 cm done
clear
D) 22.5 cm done
clear
View Solution play_arrow

question_answer27) Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact convex. The effective power of the combination is [CBSE PMT 1990; RPMT 2001]
A) 45 dioptres done
clear
B) 9 dioptres done
clear
C) 1/9 dioptre done
clear
D) 6 dioptres done
clear
View Solution play_arrow

question_answer28) An object is placed at a distance of \[f/2\] from a convex lens. The image will be [CPMT 1974, 89]
A) At one of the foci, virtual and double its size done
clear
B) At 3f / 2, real and inverted done
clear
C) At 2f, virtual and erect done
clear
D) None of these done
clear
View Solution play_arrow

question_answer29) A double convex thin lens made of glass (refractive index \[\mu \] = 1.5) has both radii of curvature of magnitude 20 cm. Incident light rays parallel to the axis of the lens will converge at a distance L such that [MNR 1991; MP PET 1996; UPSEAT 2000; Pb PET 2004]
A) L = 20 cm done
clear
B) L = 10 cm done
clear
C) L = 40 cm done
clear
D) L = 20 / 3 cm done
clear
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question_answer30) A lens behaves as a converging lens in air and a diverging lens in water. The refractive index of the material is [CPMT 1991; NCERT 1979; BHU 2005]
A) Equal to unity done
clear
B) Equal to 1.33 done
clear
C) Between unity and 1.33 done
clear
D) Greater than 1.33 done
clear
View Solution play_arrow

question_answer31) A biconvex lens forms 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 [MP PET 1994]
A) Disappear done
clear
B) Remain as real image still done
clear
C) Be virtual and of the same size as the object done
clear
D) Suffer from aberrations done
clear
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question_answer32) The radius of curvature of convex surface of a thin planoconvex lens is 15 cm and refractive index of its material is 1.6. The power of the lens will be [MP PMT 1994]
A) \[+1\,D\] done
clear
B) \[2\,D\] done
clear
C) \[+\,3\,D\] done
clear
D) \[+\,4\,D\] done
clear
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question_answer33) Focal length of a convex lens will be maximum for [MP PMT 1994]
A) Blue light done
clear
B) Yellow light done
clear
C) Green light done
clear
D) Red light done
clear
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question_answer34) 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 or light is [CBSE PMT 1995]
A) \[\frac{{{A}_{1}}+{{A}_{2}}}{2}\] done
clear
B) \[{{\left[ \frac{1}{{{A}_{1}}}+\frac{1}{{{A}_{2}}} \right]}^{1}}\] done
clear
C) \[\sqrt{{{A}_{1}}{{A}_{2}}}\] done
clear
D) \[{{\left[ \frac{\sqrt{{{A}_{1}}}+\sqrt{{{A}_{2}}}}{2} \right]}^{2}}\] done
clear
View Solution play_arrow

question_answer35) Two lenses of power 6D and ? 2D are combined to form a single lens. The focal length of this lens will be [MP PET 2003]
A) \[\frac{3}{2}\] m done
clear
B) \[\frac{1}{4}\]\[m\] done
clear
C) 4 m done
clear
D) \[\frac{1}{8}\]\[m\] done
clear
View Solution play_arrow

question_answer36) A combination of two thin lenses with focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\] respectively forms an image of distant object at distance 60 cm when lenses are in contact. The position of this image shifts by 30 cm towards the combination when two lenses are separated by 10 cm. The corresponding values of \[{{f}_{1}}\] and \[{{f}_{2}}\] are [AIIMS 1995]
A) \[30\] \[cm,\]\[60\]\[cm\] done
clear
B) \[20\]\[cm\], \[30\]\[cm\] done
clear
C) \[15\]\[cm,\] \[20\]\[cm\] done
clear
D) \[12\] \[cm,\] \[15\]\[cm\] done
clear
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question_answer37) An achromatic combination of lenses is formed by joining [BHU 1995; Pb. PMT 2000, 04]
A) 2 convex lenses done
clear
B) 2 concave lenses done
clear
C) 1 convex lens and 1 concave lens done
clear
D) Convex lens and plane mirror done
clear
View Solution play_arrow

question_answer38) A plano convex lens \[(f=20cm)\]is silvered at plane surface. Now f will be [BHU 1995; DPMT 2001; MP PMT 2005]
A) 20 cm done
clear
B) 40 cm done
clear
C) 30 cm done
clear
D) 10 cm done
clear
View Solution play_arrow

question_answer39) If the central portion of a convex lens is wrapped in black paper as shown in the figure [Manipal MEE 1995; KCET 2001]
A) No image will be formed by the remaining portion of the lens done
clear
B) The full image will be formed but it will be less bright done
clear
C) The central portion of the image will be missing done
clear
D) There will be two images each produced by one of the exposed portions of the lens done
clear
View Solution play_arrow

question_answer40) A diminished image of an object is to be obtained on a screen 1.0 m from it. This can be achieved by appropriately placing [IIT JEE 1995]
A) A convex mirror of suitable focal length done
clear
B) A concave mirror of suitable focal length done
clear
C) A concave lens of suitable focal length done
clear
D) A convex lens of suitable focal length less than 0.25 m done
clear
View Solution play_arrow

question_answer41) The focal length of convex lens is 30 cm and the size of image is quarter of the object, then the object distance is [AFMC 1995]
A) 150 cm done
clear
B) 60 cm done
clear
C) 30 cm done
clear
D) 40 cm done
clear
View Solution play_arrow

question_answer42) A convex lens forms a real image of a point object placed on its principal axis. If the upper half of the lens is painted black, the image will [MP PET 1995]
A) Be shifted downwards done
clear
B) Be shifted upwards done
clear
C) Not be shifted done
clear
D) Shift on the principal axis done
clear
View Solution play_arrow

question_answer43) In the figure, an air lens of radii of curvature 10 cm (\[{{R}_{1}}\] = \[{{R}_{2}}\] = 10 cm) is cut in a cylinder of glass\[(\mu =1.5)\]. The focal length and the nature of the lens is [MP PET 1995; Pb. PET 2000]
A) 15 cm, concave done
clear
B) 15 cm, convex done
clear
C) \[\infty \], neither concave nor convex done
clear
D) 0, concave done
clear
View Solution play_arrow

question_answer44) A lens (focal length 50 cm) forms the image of a distant object which subtends an angle of 1 milliradian at the lens. What is the size of the image [MP PMT 1995]
A) 5 mm done
clear
B) 1 mm done
clear
C) 0.5 mm done
clear
D) 0.1 mm done
clear
View Solution play_arrow

question_answer45) A convex lens of focal length 12 cm is made of glass of \[\mu =\frac{3}{2}\]. What will be its focal length when immersed in liquid of \[\mu =\frac{5}{4}\] [MP PMT 1995, 2003]
A) 6 cm done
clear
B) 12 cm done
clear
C) 24 cm done
clear
D) 30 cm done
clear
View Solution play_arrow

question_answer46) Two thin lenses of focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\] are in contact and coaxial. The combination is equivalent to a single lens of power [MP PET 1996, 98; MP PMT 1998; DCE 2000; UP SEAT 2005]
A) \[{{f}_{1}}+{{f}_{2}}\] done
clear
B) \[\frac{{{f}_{1}}{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}\] done
clear
C) \[\frac{1}{2}({{f}_{1}}+{{f}_{2}})\] done
clear
D) \[\frac{{{f}_{1}}+{{f}_{2}}}{{{f}_{1}}{{f}_{2}}}\] done
clear
View Solution play_arrow

question_answer47) A plano convex lens is made of glass of refractive index 1.5. The radius of curvature of its convex surface is R. Its focal length is [RPET 2003]
A) R/ 2 done
clear
B) R done
clear
C) 2R done
clear
D) 1.5 R done
clear
View Solution play_arrow

question_answer48) Two lenses have focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\] and their dispersive powers are \[{{\omega }_{1}}\] and \[{{\omega }_{2}}\] respectively. They will together form an achromatic combination if
A) \[{{\omega }_{1}}{{f}_{1}}={{\omega }_{2}}{{f}_{2}}\] done
clear
B) \[{{\omega }_{1}}{{f}_{2}}+{{\omega }_{2}}{{f}_{1}}=0\] done
clear
C) \[{{\omega }_{1}}+{{f}_{1}}={{\omega }_{2}}+{{f}_{2}}\] done
clear
D) \[{{\omega }_{1}}{{f}_{1}}={{\omega }_{2}}{{f}_{2}}\] done
clear
View Solution play_arrow

question_answer49) The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens is 15 cm, then the nature and focal length of the other lens would be [MP PET 1997]
A) Convex, 9 cm done
clear
B) Concave, 9 cm done
clear
C) Convex, 25 cm done
clear
D) Concave, 25 cm done
clear
View Solution play_arrow

question_answer50) A thin double convex lens has radii of curvature each of magnitude 40 cm and is made of glass with refractive index 1.65. Its focal length is nearly [MP PMT 1997]
A) 20 cm done
clear
B) 31 cm done
clear
C) 35 cm done
clear
D) 50 cm done
clear
View Solution play_arrow

question_answer51) The plane surface of a planoconvex lens of focal length f is silvered. It will behave as [MP PMT/PET 1998]
A) Plane mirror done
clear
B) Convex mirror of focal length 2\[f\] done
clear
C) Concave mirror of focal length \[f/2\] done
clear
D) None of the above done
clear
View Solution play_arrow

question_answer52) An equiconvex lens of glass of focal length 0.1 metre is cut along a plane perpendicular to principle axis into two equal parts. The ratio of focal length of new lenses formed is [MP PET 1999; DPMT 2000]
A) 1 : 1 done
clear
B) 1 : 2 done
clear
C) 2 : 1 done
clear
D) 2 :\[\frac{1}{2}\] done
clear
View Solution play_arrow

question_answer53) A lens of refractive index \[n\] is put in a liquid of refractive index \[n'\] of focal length of lens in air is \[f\], its focal length in liquid will be [MP PET 1999]
A) \[\frac{fn'(n1)}{n'n}\] done
clear
B) \[\frac{f(n'n)}{n'(n1)}\] done
clear
C) \[\frac{n'(n1)}{f(n'n)}\] done
clear
D) \[\frac{fn'\,\,n}{nn'}\] done
clear
View Solution play_arrow

question_answer54) An object of height 1.5 cm is placed on the axis of a convex lens of focal length 25 cm. A real image is formed at a distance of 75 cm from the lens. The size of the image will be [MP PET 1999]
A) 4.5 cm done
clear
B) 3.0 cm done
clear
C) 0.75 cm done
clear
D) 0.5 cm done
clear
View Solution play_arrow

question_answer55) A symmetric double convex lens is cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4 D, the power of a cut lens will be [MP PMT 1999]
A) 2 D done
clear
B) 3 D done
clear
C) 4 D done
clear
D) 5 D done
clear
View Solution play_arrow

question_answer56) A plane convex lens is made of refractive index 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is [CBSE PMT 1999; Pb. PMT 1999; BHU 2001; Very Similar to BHU 2003]
A) 50 cm done
clear
B) 100 cm done
clear
C) 200 cm done
clear
D) 400 cm done
clear
View Solution play_arrow

question_answer57) 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 behave as a [IITJEE 1999]
A) Convergent lens of focal length 3.5 R done
clear
B) Convergent lens of focal length 3.0 R done
clear
C) Divergent lens of focal length 3.5 R done
clear
D) Divergent lens of focal length 3.0 R done
clear
View Solution play_arrow

question_answer58) A convex lens of focal length 0.5 m and concave lens of focal length 1 m are combined. The power of the resulting lens will be [CPMT 1999; JIPMER 2000]
A) 1 D done
clear
B)  1 D done
clear
C) 0.5 D done
clear
D) 0.5 D done
clear
View Solution play_arrow

question_answer59) A double convex lens is made of glass of refractive index 1.5. If its focal length is 30 cm, then radius of curvature of each of its curved surface is [Bihar CEET 1995]
A) 10 cm done
clear
B) 15 cm done
clear
C) 18 cm done
clear
D) None of these done
clear
View Solution play_arrow

question_answer60) A thin lens made of glass of refractive index 1.5 has a front surface + 11 D power and back surface  6 D. If this lens is submerged in a liquid of refractive index 1.6, the resulting power of the lens is [SCRA 1994]
A) 0.5 D done
clear
B) + 0.5 D done
clear
C)  0.625 D done
clear
D) + 0.625 D done
clear
View Solution play_arrow

question_answer61) An object is placed first at infinity and then at 20 cm from the object side focal plane of the convex lens. The two images thus formed are 5 cm apart. The focal length of the lens is [SCRA 1994]
A) 5 cm done
clear
B) 10 cm done
clear
C) 15 cm done
clear
D) 20 cm done
clear
View Solution play_arrow

question_answer62) The distance between an object and the screen is 100 cm. A lens produces an image on the screen when placed at either of the positions 40 cm apart. The power of the lens is [SCRA 1994]
A) \[\approx \] 3 dioptres done
clear
B) \[\approx \] 5 dioptres done
clear
C) \[\approx \] 7 diopters done
clear
D) \[\approx \] 9 diopters done
clear
View Solution play_arrow

question_answer63) The image distance of an object placed 10 cm in front of a thin lens of focal length + 5 cm is [SCRA 1994]
A) 6.5 cm done
clear
B) 8.0 cm done
clear
C) 9.5 cm done
clear
D) 10.0 cm done
clear
View Solution play_arrow

question_answer64) A achromatic combination is made with a lens of focal length \[f\] and dispersive power \[\omega \] with a lens having dispersive power of \[2\omega \]. The focal length of second will be [RPET 1997]
A) 2 f done
clear
B) \[f/2\] done
clear
C) \[f/2\] done
clear
D) ? 2 f done
clear
View Solution play_arrow

question_answer65) A biconvex lens with equal radii curvature has refractive index 1.6 and focal length 10 cm. Its radius of curvature will be [MP PET 2003]
A) 20 cm done
clear
B) 16 cm done
clear
C) 10 cm done
clear
D) 12 cm done
clear
View Solution play_arrow

question_answer66) A convex lens [RPMT 1997]
A) Converges light rays done
clear
B) Diverges light rays done
clear
C) Form real images always done
clear
D) Always forms virtual images done
clear
View Solution play_arrow

question_answer67) The focal length of a combination of lenses formed with lenses having powers of + 2.50 D and  3.75 D will be [RPMT 1997]
A)  20 cm done
clear
B)  40 cm done
clear
C)  60 cm done
clear
D)  80 cm done
clear
View Solution play_arrow

question_answer68) Focal length of a converging lens in air is R. If it is dipped in water of refractive index 1.33, then its focal length will be around (Refractive index of lens material is 1.5) [RPMT 1997; EAMCET (Med.) 1995]
A) R done
clear
B) 2R done
clear
C) 4R done
clear
D) R / 2 done
clear
View Solution play_arrow

question_answer69) Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens when immersed in a liquid of refractive index of 1.25 will be [CBSE PMT 1993]
A) 10 cm done
clear
B) 2.5 cm done
clear
C) 5 cm done
clear
D) 7.5 cm done
clear
View Solution play_arrow

question_answer70) The focal length of a convex lens depends upon [AFMC 1994]
A) Frequency of the light ray done
clear
B) Wavelength of the light ray done
clear
C) Both (a) and (b) done
clear
D) None of these done
clear
View Solution play_arrow

question_answer71) 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 [CBSE PMT 1996; AFMC 2002]
A) + 6.5D done
clear
B)  6.5 D done
clear
C) + 7.5 D done
clear
D)  0.75 D done
clear
View Solution play_arrow

question_answer72) \[{{f}_{v}}\]and \[{{f}_{r}}\] are the focal lengths of a convex lens for violet and red light respectively and \[{{F}_{v}}\] and \[{{F}_{r}}\]are the focal lengths of a concave lens for violet and red light respectively, then [CBSE PMT 1996]
A) \[{{f}_{v}}<{{f}_{r}}\] and \[{{F}_{v}}>{{F}_{r}}\] done
clear
B) \[{{f}_{v}}<{{f}_{R}}\] and \[{{F}_{v}}<{{F}_{r}}\] done
clear
C) \[{{f}_{c}}>{{f}_{r}}\] and \[{{F}_{v}}>{{F}_{r}}\] done
clear
D) \[{{f}_{v}}>{{f}_{r}}\] and \[{{F}_{v}}<{{F}_{r}}\] done
clear
View Solution play_arrow

question_answer73) If a lens is cut into two pieces perpendicular to the principal axis and only one part is used, the intensity of the image [CPMT 1996]
A) Remains same done
clear
B) \[\frac{1}{2}\] times done
clear
C) 2 times done
clear
D) Infinite done
clear
View Solution play_arrow

question_answer74) A convex lens of focal length \[f\] produces an image \[\frac{1}{n}\] times than that of the size of the object. The distance of the object from the lens is [BHU 1997; JIPMER 2001, 02]
A) \[nf\] done
clear
B) \[\frac{f}{n}\] done
clear
C) \[(n+1)\,f\] done
clear
D) \[(n1)\,f\] done
clear
View Solution play_arrow

question_answer75) Two thin lenses whose powers are +2D and 4D respectively combine, then the power of combination is [AFMC 1998; CPMT 1996; Very Similar to BHU 2004]
A)  2D done
clear
B) + 2D done
clear
C)  4D done
clear
D) + 4D done
clear
View Solution play_arrow

question_answer76) A substance is behaving as convex lens in air and concave in water, then its refractive index is [BHU 1998]
A) Smaller than air done
clear
B) Greater than both air and water done
clear
C) Greater than air but less than water done
clear
D) Almost equal to water done
clear
View Solution play_arrow

question_answer77) A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a [SCRA 1998]
A) Convex mirror of focal length 10 cm done
clear
B) Concave mirror of focal length 40 cm done
clear
C) Concave mirror of focal length 60 cm done
clear
D) Concave mirror of focal length 10 cm done
clear
View Solution play_arrow

question_answer78) A convex lens is used to form real image of an object on a screen. It is observed that even when the positions of the object and that screen are fixed there are two positions of the lens to form real images. If the heights of the images are 4 cm and 9 cm respectively, the height of the object is [AMU (Med.) 1999]
A) 2.25 cm done
clear
B) 6.00 cm done
clear
C) 6.50 cm done
clear
D) 36.00 cm done
clear
View Solution play_arrow

question_answer79) A convex lens of power + 6D is placed in contact with a concave lens of power ? 4D. What is the nature and focal length of the combination [AMU (Engg.) 1999]
A) Concave, 25 cm done
clear
B) Convex, 50 cm done
clear
C) Concave, 20 cm done
clear
D) Convex, 100 cm done
clear
View Solution play_arrow

question_answer80) A double convex lens of glass of m = 1.5 has radius of curvature of each of its surface is 0.2 m. The power of the lens is [JIPMER 1999]
A) + 10 dioptres done
clear
B)  10 dioptres done
clear
C)  5 dioptres done
clear
D) +5 dioptres done
clear
View Solution play_arrow

question_answer81) A lens of focal power 0.5 D is [JIPMER 1999]
A) A convex lens of focal length 0.5 m done
clear
B) A concave lens of focal length 0.5 m done
clear
C) A convex lens of focal length 2 m done
clear
D) A concave lens of focal length 2 m done
clear
View Solution play_arrow

question_answer82) A lens which has focal length of 4 cm and refractive index of 1.4 is immersed in a liquid of refractive index 1.6, then the focal length will be [RPMT 1999]
A)  12.8 cm done
clear
B) 32 cm done
clear
C) 12.8 cm done
clear
D)  32 cm done
clear
View Solution play_arrow

question_answer83) A convex lens has 9 cm focal length and a concave lens has 18 cm focal length. The focal length of the combination in contact will be [RPMT 1999]
A) 9 cm done
clear
B)  18 cm done
clear
C)  9 cm done
clear
D) 18 cm done
clear
View Solution play_arrow

question_answer84) A double convex thin lens made of glass of refractive index 1.6 has radii of curvature 15 cm each. The focal length of this lens when immersed in a liquid of refractive index 1.63 is [UPSEAT 2000; Pb. PET 2004]
A)  407 cm done
clear
B) 250 cm done
clear
C) 125 cm done
clear
D) 25 cm done
clear
View Solution play_arrow

question_answer85) A lens of power + 2 diopters is placed in contact with a lens of power ? 1 diopoter. The combination will behave like [UPSEAT 2000]
A) A divergent lens of focal length 50 cm done
clear
B) A convergent lens of focal length 50 cm done
clear
C) A convergent lens of focal length 100 cm done
clear
D) A divergent lens of focal length 100 cm done
clear
View Solution play_arrow

question_answer86) Chromatic aberration of lens can be corrected by [AFMC 2000]
A) Reducing its aperature done
clear
B) Proper polishing of its two surfaces done
clear
C) Suitably combining it with another lens done
clear
D) Providing different suitable curvature to its two surfaces done
clear
View Solution play_arrow

question_answer87) The relation between n1 and n2, if behaviour of light rays is as shown in figure is [KCET 2000]
A) \[{{n}_{1}}>>{{n}_{2}}\] done
clear
B) \[{{n}_{2}}>{{n}_{1}}\] done
clear
C) \[{{n}_{1}}>{{n}_{2}}\] done
clear
D) \[{{n}_{1}}={{n}_{2}}\] done
clear
View Solution play_arrow

question_answer88) A candle placed 25 cm from a lens, forms an image on a screen placed 75 cm on the other end of the lens. The focal length and type of the lens should be [KCET 2000]
A) + 18.75 cm and convex lens done
clear
B)  18.75 cm and concave lens done
clear
C) + 20.25 cm and convex lens done
clear
D)  20.25 cm and concave lens done
clear
View Solution play_arrow

question_answer89) We combined a convex lens of focal length f1 and concave lens of focal lengths f2 and their combined focal length was F. The combination of these lenses will behave like a concave lens, if [KCET 2000]
A) f1 > f2 done
clear
B) f1 < f2 done
clear
C) f1 = f2 done
clear
D) f1 \[\le \] f2 done
clear
View Solution play_arrow

question_answer90) In a planoconvex lens the radius of curvature of the convex lens is 10 cm. If the plane side is polished, then the focal length will be (Refractive index = 1.5) [CBSE PMT 2000; BHU 2004]
A) 10.5 cm done
clear
B) 10 cm done
clear
C) 5.5 cm done
clear
D) 5 cm done
clear
View Solution play_arrow

question_answer91) 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 [MP PMT 2000]
A) 7.5 cm done
clear
B) 15.0 cm done
clear
C) 75 cm done
clear
D) 5.0 cm done
clear
View Solution play_arrow

question_answer92) A convex lens has a focal length f. It is cut into two parts along the dotted line as shown in the figure. The focal length of each part will be [MP PET 2000]
A) \[\frac{f}{2}\] done
clear
B) f done
clear
C) \[\frac{3}{2}f\] done
clear
D) 2f done
clear
View Solution play_arrow

question_answer93) An object has image thrice of its original size when kept at 8 cm and 16 cm from a convex lens. Focal length of the lens is [UPSEAT 2001]
A) 8 cm done
clear
B) 16 cm done
clear
C) Between 8 cm and 16 cm done
clear
D) Less than 8 cm done
clear
View Solution play_arrow

question_answer94) The combination of a convex lens (f = 18 cm) and a thin concave lens (f = 9 cm) is [AMU (Engg.) 2001]
A) A concave lens (f = 18 cm) done
clear
B) A convex lens (f = 18 cm) done
clear
C) A convex lens (f = 6 cm) done
clear
D) A concave lens (f = 6 cm) done
clear
View Solution play_arrow

question_answer95) A convex lens forms a real image of an object for its two different positions on a screen. If height of the image in both the cases be 8 cm and 2 cm, then height of the object is [KCET 2000, 01]
A) 16 cm done
clear
B) 8 cm done
clear
C) 4 cm done
clear
D) 2 cm done
clear
View Solution play_arrow

question_answer96) A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are joined together. The power of the combination will be [MP PMT 2001]
A) ? 16 D done
clear
B) + 16 D done
clear
C) ? 6 D done
clear
D) + 6 D done
clear
View Solution play_arrow

question_answer97) The unit of focal power of a lens is [KCET 2001]
A) Watt done
clear
B) Horse power done
clear
C) Dioptre done
clear
D) Lux done
clear
View Solution play_arrow

question_answer98) A thin lens made of glass of refractive index m = 1.5 has a focal length equal to 12 cm in air. It is now immersed in water \[\left( \mu \,=\,\frac{4}{3} \right)\]. Its new focal length is [UPSEAT 2002]
A) 48 cm done
clear
B) 36 cm done
clear
C) 24 cm done
clear
D) 12 cm done
clear
View Solution play_arrow

question_answer99) Figure given below shows a beam of light converging at point P. When a convex lens of focal length 16 cm is introduced in the path of the beam at a place O shown by dotted line such that OP becomes the axis of the lens, the beam converges at a distance x from the lens. The value x will be equal to [AMU (Med.) 2002]
A) 12 cm done
clear
B) 24 cm done
clear
C) 36 cm done
clear
D) 48 cm done
clear
View Solution play_arrow

question_answer100) If two + 5 D lenses are mounted at some distance apart, the equivalent power will always be negative if the distance is [UPSEAT 2002]
A) Greater than 40 cm done
clear
B) Equal to 40 cm done
clear
C) Equal to 10 cm done
clear
D) Less than 10 cm done
clear
View Solution play_arrow

question_answer101) A convex lens produces a real image m times the size of the object. What will be the distance of the object from the lens [JIPMER 2002]
A) \[\left( \frac{m+1}{m} \right)f\] done
clear
B) (m ?1)f done
clear
C) \[\left( \frac{m1}{m} \right)f\] done
clear
D) \[\frac{m+1}{f}\] done
clear
View Solution play_arrow

question_answer102) A convex lens is made up of three different materials as shown in the figure. For a point object placed on its axis, the number of images formed are [KCET 2002]
A) 1 done
clear
B) 5 done
clear
C) 4 done
clear
D) 3 done
clear
View Solution play_arrow

question_answer103) An object is placed 12 cm to the left of a converging lens of focal length 8 cm. Another converging lens of 6 cm focal length is placed at a distance of 30 cm to the right of the first lens. The second lens will produce [KCET 2002]
A) No image done
clear
B) A virtual enlarged image done
clear
C) A real enlarged image done
clear
D) A real smaller image done
clear
View Solution play_arrow

question_answer104) If convex lens of focal length 80cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power [AFMC 2002]
A) + 6.5 D done
clear
B) ? 6.5 D done
clear
C) + 7.5 D done
clear
D) ? 0.75 D done
clear
View Solution play_arrow

question_answer105) A point object O is placed in front of a glass rod having spherical end of radius of curvature 30 cm. The image would be formed at [Orissa JEE 2002]
A) 30 cm left done
clear
B) Infinity done
clear
C) 1 cm to the right done
clear
D) 18 cm to the left done
clear
View Solution play_arrow

question_answer106) The focal length of lens of refractive index 1.5 in air is 30 cm. When it is immersed in a liquid of refractive index \[\frac{4}{3}\], then its focal length in liquid will be [BHU 2002]
A) 30 cm done
clear
B) 60 cm done
clear
C) 120 cm done
clear
D) 240 cm done
clear
View Solution play_arrow

question_answer107) Two thin lenses of focal lengths f1 and f2 are in contact. The focal length of this combination is [MP PET 2002]
A) \[\frac{{{f}_{1}}{{f}_{2}}}{{{f}_{1}}{{f}_{2}}}\] done
clear
B) \[\frac{{{f}_{1}}{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}\] done
clear
C) \[\frac{2{{f}_{1}}{{f}_{2}}}{{{f}_{1}}{{f}_{2}}}\] done
clear
D) \[\frac{2{{f}_{1}}{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}\] done
clear
View Solution play_arrow

question_answer108) 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 [CBSE PMT 2003]
A) Become infinite done
clear
B) Become small, but non?zero done
clear
C) Remain unchanged done
clear
D) Become zero done
clear
View Solution play_arrow

question_answer109) 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 each half in case (i), and of each half in case (ii), respectively Choose the correct statement from the following [CBSE PMT 2003]
A) \[{f}'=2f,\,{f}''=f\] done
clear
B) \[{f}'=f,\,{f}''=f\] done
clear
C) \[{f}'=2f,\,{f}''=2f\] done
clear
D) \[{f}'=f,\,{f}''=2f\] done
clear
View Solution play_arrow

question_answer110) The sun makes 0.5o angle on earth surface. Its image is made by convex lens of 50 cm focal length. The diameter of the image will be [CPMT 2003]
A) 5 mm done
clear
B) 4.36 mm done
clear
C) 7 mm done
clear
D) None of these done
clear
View Solution play_arrow

question_answer111) The chromatic Aberration in lenses becomes due to [CPMT 2003]
A) Disimilarity of main axis of rays done
clear
B) Disimilarity of radii of curvature done
clear
C) Variation of focal length of lenses with wavelength done
clear
D) None of these done
clear
View Solution play_arrow

question_answer112) If aperture of lens is halved then image will be [AFMC 2003]
A) No effect on size done
clear
B) Intensity of image decreases done
clear
C) Both (a) and (b) done
clear
D) None of these done
clear
View Solution play_arrow

question_answer113) When the convergent nature of a convex lens will be less as compared with air [AFMC 2003]
A) In water done
clear
B) In oil done
clear
C) In both (a) and (b) done
clear
D) None of these done
clear
View Solution play_arrow

question_answer114) An achromatic combination of lenses produces [KCET 1993; JIPMER 1997]
A) Coloured images done
clear
B) Highly enlarged image done
clear
C) Images in black and white done
clear
D) Images unaffected by variation of refractive index with wavelength done
clear
View Solution play_arrow

question_answer115) In a parallel beam of white light is incident on a converging lens, the colour which is brought to focus nearest to the lens is [JIPMER 1999]
A) Violet done
clear
B) Red done
clear
C) The mean colour done
clear
D) All the colours together done
clear
View Solution play_arrow

question_answer116) A magnifying glass is to be used at the fixed object distance of 1 inch. If it is to produce an erect image magnified 5 times its focal length should be [MP PMT 1990]
A) 0.2 inch done
clear
B) 0.8 inch done
clear
C) 1.25 inch done
clear
D) 5 inch done
clear
View Solution play_arrow

question_answer117) A film projector magnifies a 100 cm2 film strip on a screen. If the linear magnification is 4, the area of magnified film on the screen is [NCERT 1980; CPMT 1977, 91; MP PET 1985, 89; RPMT 2001; BCEC 2005]
A) 1600 cm2 done
clear
B) 400 cm2 done
clear
C) 800 cm2 done
clear
D) 200 cm2 done
clear
View Solution play_arrow

question_answer118) An object placed 10 cm in front of a lens has an image 20 cm behind the lens. What is the power of the lens (in dioptres) [MP PMT 1995]
A) 1.5 done
clear
B) 3.0 done
clear
C) ? 15.0 done
clear
D) + 15.0 done
clear
View Solution play_arrow

question_answer119) A beam of parallel rays is brought to a focus by a planoconvex lens. A thin concave lens of the same focal length is joined to the first lens. The effect of this is [KCET 2004]
A) The focal point shifts away from the lens by a small distance done
clear
B) The focus remains undisturbed done
clear
C) The focus shifts to infinity done
clear
D) The focal point shifts towards the lens by a small distance done
clear
View Solution play_arrow

question_answer120) A thin planoconvex lens acts like a concave mirror of focal length 0.2 m when silvered from its plane surface. The refractive index of the material of the lens is 1.5. The radius of curvature of the convex surface of the lens will be [KCET 2004]
A) 0.4 m done
clear
B) 0.2 m done
clear
C) 0.1 m done
clear
D) 0.75 m done
clear
View Solution play_arrow

question_answer121) A point object is placed at the center of a glass sphere of radius 6 cm and refractive index 1.5. The distance of the virtual image from the surface of the sphere is [IITJEE (Screening) 2004]
A) 2 cm done
clear
B) 4 cm done
clear
C) 6 cm done
clear
D) 12 cm done
clear
View Solution play_arrow

question_answer122) In order to obtain a real image of magnification 2 using a converging lens of focal length 20 cm, where should an object be placed [AFMC 2004]
A) 50 cm done
clear
B) 30 cm done
clear
C) ? 50 cm done
clear
D) ? 30 cm done
clear
View Solution play_arrow

question_answer123) A planoconvex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of the size of the object [AIEEE 2004]
A) 20 cm done
clear
B) 30 cm done
clear
C) 60 cm done
clear
D) 80 cm done
clear
View Solution play_arrow

question_answer124) A double convex lens \[({{R}_{1}}={{R}_{2}}=10\,cm)\]\[(\mu =1.5)\] having focal length equal to the focal length of a concave mirror. The radius of curvature of the concave mirror is [Orssia PMT 2004]
A) 10 cm done
clear
B) 20 cm done
clear
C) 40 cm done
clear
D) 15 cm done
clear
View Solution play_arrow

question_answer125) At what distance from a convex lens of focal length 30 cm, an object should be placed so that the size of the image be 1/2 of the object [J&K CET 2004]
A) 30 cm done
clear
B) 60 cm done
clear
C) 15 cm done
clear
D) 90 cm done
clear
View Solution play_arrow

question_answer126) A planoconvex lens is made of refractive index of 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is [Pb. PET 2000]
A) 400 cm done
clear
B) 200 cm done
clear
C) 100 cm done
clear
D) 50 cm done
clear
View Solution play_arrow

question_answer127) The radius of the convex surface of planoconvex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is [CPMT 2004]
A) 30 cm done
clear
B) 50 cm done
clear
C) 20 cm done
clear
D) 40 cm done
clear
View Solution play_arrow

question_answer128) A combination of two thin convex lenses of focal length 0.3 m and 0.1 m will have minimum spherical and chromatic aberrations if the distance between them is [UPSEE 2004]
A) 0.1 m done
clear
B) 0.2 m done
clear
C) 0.3 m done
clear
D) 0.4 m done
clear
View Solution play_arrow

question_answer129) A biconvex lens made of glass (refractive index 1.5) is put in a liquid of refractive index 1.7. Its focal length will [UPSEAT 2004]
A) Decrease and change sign done
clear
B) Increase and change sign done
clear
C) Decrease and remain of the same sign done
clear
D) Increase and remain of the same sign done
clear
View Solution play_arrow

question_answer130) Spherical aberration in a lens [UPSEAT 2004]
A) Is minimum when most of the deviation is at the first surface done
clear
B) Is minimum when most of the deviation is at the second surface done
clear
C) Is minimum when the total deviation is equally distributed over the two surface done
clear
D) Does not depend on the above consideration done
clear
View Solution play_arrow

question_answer131) The focal lengths of convex lens for red and blue light are 100 cm and 96.8 cm respectively. The dispersive power of material of lens is [Pb. PET 2003]
A) 0.325 done
clear
B) 0.0325 done
clear
C) 0.98 done
clear
D) 0.968 done
clear
View Solution play_arrow

question_answer132) The power of an achromatic convergent lens of two lenses is + 2D. The power of convex lens is + 5D. The ratio of dispersive power of convex and concave lens will be [Pb. PET 2003]
A) 5 : 3 done
clear
B) 3 : 5 done
clear
C) 2 : 5 done
clear
D) 5 : 2 done
clear
View Solution play_arrow

question_answer133) The focal lengths for violet, green and red light rays are \[{{f}_{V}},{{f}_{G}}\]and \[{{f}_{R}}\] respectively. Which of the following is the true relationship [BHU 2004; CBSE PMT 1997]
A) \[{{f}_{R}}<{{f}_{G}}<{{f}_{V}}\] done
clear
B) \[{{f}_{V}}<{{f}_{G}}<{{f}_{R}}\] done
clear
C) \[{{f}_{G}}<{{f}_{R}}<{{f}_{V}}\] done
clear
D) \[{{f}_{G}}<{{f}_{V}}<{{f}_{R}}\] done
clear
View Solution play_arrow

question_answer134) Two lenses of power + 12 and ? 2 diopters are placed in contact. The combined focal length of the combination will be [Pb. PET 2004]
A) 8.33 cm done
clear
B) 1.66 cm done
clear
C) 12.5 cm done
clear
D) 10 cm done
clear
View Solution play_arrow

question_answer135) When light rays from the sun fall on a convex lens along a direction parallel to its axis [MP PMT 2004]
A) Focal length for all colours is the same done
clear
B) Focal length for violet colour is the shortest done
clear
C) Focal length for yellow colour is the longest done
clear
D) Focal length for red colour is the shortest done
clear
View Solution play_arrow

question_answer136) A convex lens is in contact with concave lens. The magnitude of the ratio of their focal length is 2/3. Their equivalent focal length is 30 cm. What are their individual focal lengths [IITJEE (Screening) 2005]
A) ? 75, 50 done
clear
B) ? 10, 15 done
clear
C) 75, 50 done
clear
D) ? 15, 10 done
clear
View Solution play_arrow

question_answer137) A thin glass (refractive index 1.5) lens has optical power of \[\,5D\] in air. It's optical power in a liquid medium with refractive index 1.6 will be [AIEEE 2005]
A) 25 D done
clear
B) ? 25 D done
clear
C) 1 D done
clear
D) None of these done
clear
View Solution play_arrow

question_answer138) The plane faces of two identical planoconvex lenses each having focal length of 40 cm are pressed against each other to form a usual convex lens. The distance from this lens, at which an object must be placed to obtain a real, inverted image with magnification one is [NCERT 1980; CPMT 1981; MP PMT 1999; UPSEAT 1999]
A) 80 cm done
clear
B) 40 cm done
clear
C) 20 cm done
clear
D) 162 cm done
clear
View Solution play_arrow

question_answer139) If two lenses of +5 diopters are mounted at some distance apart, the equivalent power will always be negative if the distance is [BCECE 2005]
A) Greater than 40 cm done
clear
B) Equal to 40 cm done
clear
C) Equal to 10 cm done
clear
D) Less than 10 cm done
clear
View Solution play_arrow

question_answer140) A concave lens and a convex lens have same focal length of 20 cm and both put in contact this combination is used to view an object 5 cm long kept at 20 cm from the lens combination. As compared to object the image will be [CPMT 2005]
A) Magnified and inverted done
clear
B) Reduced and erect done
clear
C) Of the same size and erect done
clear
D) Of the same size and inverted done
clear
View Solution play_arrow

question_answer141) The focal length of the field lens (which is an achromatic combination of two lenses) of telescope is 90 cm. The dispersive powers of the two lenses in the combination are 0.024 and 0.036. The focal lengths of two lenses are [CPMT 2005]
A) 30 cm and 60 cm done
clear
B) 30 cm and ? 45 cm done
clear
C) 45 cm and 90 cm done
clear
D) 15 cm and 45 cm done
clear
View Solution play_arrow

question_answer142) A combination of two thin lenses of the same material with focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\], arranged on a common axis minimizes chromatic aberration, if the distance between them is [EAMCET 2005]
A) \[\frac{({{f}_{1}}+{{f}_{2}})}{4}\] done
clear
B) \[\frac{({{f}_{1}}+{{f}_{2}})}{2}\] done
clear
C) \[({{f}_{1}}+{{f}_{2}})\] done
clear
D) \[2({{f}_{1}}+{{f}_{2}})\] done
clear
View Solution play_arrow

question_answer143) If the focal length of a double convex lens for red light is \[{{f}_{R}},\] its focal length for the violet light is [EAMCET 2005]
A) \[{{f}_{R}}\] done
clear
B) Greater than \[{{f}_{R}}\] done
clear
C) Less than \[{{f}_{R}}\] done
clear
D) \[2{{f}_{R}}\] done
clear
View Solution play_arrow

question_answer144) A thin equiconvex lens is made of glass of refractive index 1.5 and its focal length is 0.2 m, if it acts as a concave lens of 0.5 m focal length when dipped in a liquid, the refractive index of the liquid is [EAMCET 2005]
A) \[\frac{17}{8}\] done
clear
B) \[\frac{15}{8}\] done
clear
C) \[\frac{13}{8}\] done
clear
D) \[\frac{9}{8}\] done
clear
View Solution play_arrow

question_answer145) The dispersive power of the material of lens of focal length 20 cm is 0.08. The longitudinal chromatic aberration of the lens is [EAMCET 2005]
A) 0.08 cm done
clear
B) 0.08/20 cm done
clear
C) 1.6 cm done
clear
D) 0.16 cm done
clear
View Solution play_arrow