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# CBSE Class 12-science Answered

a thin stick of length f/5 is placed along principle axis of a concave mirror of focal length f such that it's image which is real and elongated just touches the stick .what is the magnification
Asked by amishavasave56.12dgatl | 27 Aug, 2021, 05:25: PM
Expert Answer
Let u be the distance between pole of concave mirror and front edge of the rod.
It is given that real and elongated image is obtained . Hence the front edge of the rod is
between F and 2F. Since it is given that image touches the rod , mirror-to-image distance
is ( u + ( f/5) ] as shown in figure because length of rod is f/5 .

we have mirror equation,  (1/v) + (1/u) = 1/f

From above expression , we get a quadratic equation , 5 u2 - 9f u - f2 = 0

From above quadratic expression we express u in terms of f as , u = 1.9 f

Magnification M = v / u

Answered by Thiyagarajan K | 28 Aug, 2021, 08:33: AM

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