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Two convex lenses A and B of focal length 10cm and 15 cm are separated by “d” distance and placed coaxially. A point object is placed on the axis at 20 cm from lens A. If final image is formed at infinity find the distance of separation “d”.

Ajit Siddharth , 14 Years ago
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anser 1 Answers
shalini goyal

Last Activity: 14 Years ago

the correct ans is 35 cm....

soln:-.....for lens "A",

                             its focal length is 10 cm and object is at 20 cm 4m it,so it means obj is at 2f....so image will b 20 cm far apart it.....n u can also find it by d formula,

                                1/f=1/v-1/u.......where f,v and u are focal length,image distance and object distance from pole,

                         now (d-20) is the object distance for lens B,

             so,1/15=1/*-1/{-(d-20)}.....where * is infinity as given.....

          hense,d-20=15

                    d=35 cm

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