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find the nature size position of image of an object placed 18cm in front of concave lens of focal length 20cm |
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Answer» tion:According to the question,Image distance, v=−15 cm (negative DUE to convex lens)Focal length, f=−20 cmLet the object distance be u.By lens FORMULA:v1−u1=f1[4PT]⇒−15 cm1−u1=−20 cm1[4pt]⇒u1=20 cm1+−15 cm1[4pt]⇒u1=60 cm3−4=60 cm−1[4pt]⇒u=−60 cmTherefore, object is placed at 60 cm away from the lens, on the same side as image.Now,Height of object, h1=5cmMagnification, m=h1h2=uvPutting value of v and u:Magnification, m=5 cmh2=−60 cm−15 cm⇒5 cmh2=41⇒h2=45 cm=1.25 cmThus, the height of the image is 1.25 cm and the POSITIVE sign means the image is virtual and erect. |
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