InterviewSolution
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InterviewSolution
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A convex lens forms an image of an object on a screen ,The height of the image is`9cm`The lens is now disiplaced between the object on the screen.the height of this image is`4cm`.the distance between the object and the screen is `90cm`A. The distance between the two positions of the lens is `30cm`B. The distance of the object from the lens in its first position is`36cm`C. The height of the object is `6cm`D. The focal length of the lens is`21.6cm` |
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Answer» Correct Answer - B,C,D `h=sqrt(h_(1)h_(2)) rArrh=6cm` `m=(h_(1))/(h) =(v)/(u) rArr (-9)/(6) =(D-x_(1))/(-x_(1))` `x_(1)=36cm rArrx_(2)=D-x_(1) rArr x_(2)=54cm` ` d=54-36=18cm` `f=(D^(2)-d^(2))/(4D) rArr f=(90^(2)-18^(2))/(4xx90)` `f=((90+18)(90-18))/(4xx90) rArr f=(108xx72)/(4xx90)=(3xx72)/(10)=21.6cm` |
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