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An image I is formed of point object O by a lens whose optic axis is AB as shown in figure. (a) State whether it is a convex lens or concave? (b) Draw a ray diagram to locate the lens and its focus. |
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Answer» SOLUTION : (i) Concave lens always forms an erect IMAGE. The given image I is on the other SIDE of the optic axis. Hence, the lens is convex. (ii) Join O with I. LINE OI cuts the optic axis AB at optical centre (P) of the lens. The dotted line shows the position of lens.  From point O, DRAW a line parallel to AB. Let it cut the dotted line at M. Join M with I. Line MI cuts the optic axis at focus (F) of the lens. |
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