Practice Test


1) How will the image formed by a convex lens be affected, if the central portion of the lens is wrapped in black paper, as shown in the figure ?


2) A converging lens has a focal length of 1 m. The minimum distance between a real object and its real image formed by this lens is


3) A lens of large aperture is found to give a blurred image of a point object. A black paper with a small hole in its centre is placed in front of the lens. Then


4) The curved face of a planoconvex lens has a radius of curvature of 250 mm. The refractive index of lens material is 1.5. The power of the lens is


5) An object 15 cm high is placed 10 cm from the optical centre of thin lens. Its image is formed 25 cm from the optical centre on the same side of the lens as the object. The height of the image is


6) The lens forms a virtual, diminished image of an object placed at 2 m from it. The size of image is half of the object. Which one of the following statements is correct regarding the nature and focal length of the lens?


7) A lens will be invisible in vacuum when the refractive index of the lens is


8) The axial or longitudinal magnification of a lens is


9) As an object gets closer to the focal point of a converging lens from infinity, its image


10) A convex lens can form a virtual image if the object is placed


11) Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact. The effective power of the combination is


12) A converging lens is used to form an image on a scree. When the upper half of the lens is covered by an opaque screen.


13) Two lenses of powers + 12 D and - 2 D are placed in contact. What will be the focal length of the combination ?


14) A convex lens A of focal length 20 cm and a concave lens B of focal length 5 cm are kept along the same axis with the distance d between them. If a parallel beam of light falling on A leaves B as a parallel beam, then distance d in cm will be


15) If the space between the lenses in the lens combination shown are filled with water, what would happen to the focal length and power of the lens combination ?
Focal length Power


16) Two thin lenses are in contact and the focal length of the combination is 80 cm. If the focal length of one lens is 20 cm, then the power of the other lens will be


17) In displacement method, the lengths of images in two positions of lens between object and screen are 9 cm and 4 cm respectively. The length of object must be


18) Two convex lenses placed in contact form the image of a distant object at P. If the lens B is moved t the right, the image will


19) A thin lens produces an upright image of the same size as the object. Then from the optical centre of the lens, the distance of the object is


20) A lens behaves as a converging lens in air and a diverging lens in water. The refractive index of the material of the lens, is


21) 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


22) A convex lens of focal length 10 cm and concave lens of focal length 20 cm are kept 5 cm apart. The focal length of the equivalent lens is


23) A screen is placed at a distance 100 cm from an illuminated object. A convex lens is placed between the source and the screen and it is attempted to form the image of the source on the screen. If no position could be obtained, the focal length of the lens


24) A parallel beam of light is incident on a converging lens parallel to its principal axis. As one moves away from the lens on the other side on its principal axis, the intensity of light


25) A point object is placed at the centre 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


26) A plano-convex lens when silvered on the plane side behaves like a concave mirror of focal length 60 cm. However, when silvered on the convex side it behaves like a concave mirror of focal length 20 cm. Then the refractive index of the lens is


27) An object is placed at a distance of 15 cm from a convex lens of a focal length 10 cm.On the other side of the lens, a convex mirror is placed at its focus such that the image formed by the combination coincides with the object itself. The focal length of he convex mirror is


28) If R be the radius of curvature of both the surface of the convex lens, then the focal length of the convex lens is :


29) When the space between the lens and mirror is filled by water, the focal length of water concave lens is


30) The radius of curvature R of each surface of convex lens is


31) Statement 1 : Spherical abberration occur in lenses of larger aperture.
Statement 2 : The two rays, paraxial and marginal rays focus at different points


32) Statement 1 : Convergent lens property of converging remain same in all mediums.
Statement 2 : Property of lens whether the ray is diverging or converging is dependent of the surrounding medium


33) A page having letters printed on it in blue, yellow and red colours is covered by a glass slab. Which of the following is correct ?


34) A light ray traveling from air to glass cannot get


35) For similar beam of incident light, image formed by ordinary reflected light is n times brighter than image formed by totally internally reflected light. The value of n is


36) 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


37) A lens of power + 2 diopters is placed in contact with a lens of power -1 diopter. The combination will behave like


38) 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


39) 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


40) Two lenses of power +12 and -2 diopters are placed in contact. What will the focal length of combination


41) 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


42) 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


43) A converging lens is used to form an image on a screen. When upper half of the lens is covered by an opaque screen


44) 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


45) 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


46) 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


47) 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


48) 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


49) A convex lens of crown glass (n =1.525) will behave as a divergent lens if immersed in


50) A divergent lens will produce


51) The minimum distance between an object and its real image formed by a convex lens is


52) 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


53) 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


54) Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact convex. The effective power of the combination is


55) A lens behaves as a converging lens in air and a diverging lens in water. The refractive index of the material is


56) 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


57) The radius of curvature of convex surface of a thin plano-convex lens is 15 cm and refractive index of its material is 1.6. The power of the lens will be


58) Focal length of a convex lens will be maximum for


59) Two lenses of power 6D and -2D are combined to form a single lens. The focal length of this lens will be


60) An achromatic combination of lenses is formed by joining


61) 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


62) The focal length of convex lens is 30 cm and the size of image is quarter of the object, then the object distance is


63) 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


64) 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


65) 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


66) 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


67) 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


68) The plane surface of a plano-convex lens of focal length f is silvered. It will behave as


69) 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


70) 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


71) 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


72) 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


73) 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


74) 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


75) 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


76) 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


77) 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


78) 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


79) The image distance of an object placed 10 cm in front of a thin lens of focal length + 5 cm is


80) A biconvex lens with equal radii curvature has refractive index 1.6 and focal length 10 cm. Its radius of curvature will be


81) A convex lens


82) The focal length of a combination of lenses formed with lenses having powers of + 2.50 D and -3.75 D will be


83) 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)


84) 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


85) The focal length of a convex lens depends upon


86) 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


87) If a lens is cut into two pieces perpendicular to the principal axis and only one part is used, the intensity of the image


88) Two thin lenses whose powers are +2D and -4D respectively combine, then the power of combination is


89) A substance is behaving as convex lens in air and concave in water, then its refractive index is


90) A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a


91) 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


92) A lens of focal power 0.5 D is


93) 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


94) 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


95) 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


96) A lens of power + 2 diopters is placed in contact with a lens of power -1 diopoter. The combination will behave like


97) Chromatic aberration of lens can be corrected by


98) 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


99) In a plano-convex 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)


100) 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


101) 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


102) The combination of a convex lens (f = 18 cm) and a thin concave lens (f = 9 cm) is


103) 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


104) 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


105) The unit of focal power of a lens is


106) If two + 5 D lenses are mounted at some distance apart, the equivalent power will always be negative if the distance is


107) 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


108) 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


109) 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


110) The chromatic Aberration in lenses becomes due to


111) If aperture of lens is halved then image will be


112) When the convergent nature of a convex lens will be less as compared with air


113) An achromatic combination of lenses produces


114) 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


115) 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


116) 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)


117) A beam of parallel rays is brought to a focus by a plano-convex lens. A thin concave lens of the same focal length is joined to the first lens. The effect of this is


118) A thin plano-convex 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


119) 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


120) A plano-convex 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


121) 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


122) A plano-convex 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


123) The radius of the convex surface of plano-convex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is


124) 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


125) A bi-convex lens made of glass (refractive index 1.5) is put in a liquid of refractive index 1.7. Its focal length will


126) Spherical aberration in a lens


127) 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


128) 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


129) When light rays from the sun fall on a convex lens along a direction parallel to its axis


130) 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


131) A thin glass (refractive index 1.5) lens has optical power of - 5 D in air. It's optical power in a liquid medium with refractive index 1.6 will be


132) The plane faces of two identical plano-convex 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


133) If two lenses of +5 diopters are mounted at some distance apart, the equivalent power will always be negative if the distance is


134) 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


135) 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


136) 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


137) The dispersive power of the material of lens of focal length 20 cm is 0.08. The longitudinal chromatic aberration of the lens is