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A convex lens is used to obtain a magnified image of an object on a screen 10 m from the lens. If the magnification is 19, find the focal length of the lens. |
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Answer» Solution :Here, DISTANCE of screen from the lens v = 10 m and magnification of image m = 19As image is being formed on the screen, the image is a real image and v is + ve. As `m=v/u`, hence `u=v/m = (10M)/19` and `-ve` As `m=v/u`, hence, `u=v/m = (10 m)/19` and `-ve` Using lens FORMULA `1/v -1/u = 1/f`, we have `1/(+10) -1/(-10/19) = 1/f rArr 1/f = 1/10 + 19/20 = 20/20 =2 `or `f=1/2 m = 0.5 m` or 50 CM |
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