Question

a concave lens forms a real and inverted image of a needle at a distance of 50 CM. from it . where is the needle placed in front of the lens if the image size is equal to the object size? also find the power of the lens.

Answer 1

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Since h'=h

We can conclude object is placed at 50 cm (remember we need to take it -50 cm)away from lens and 50 cm is radius of curvature.

P=1/f (f=radius of curvature/2)

P=1/0.25 (f Is taken in metre)

P=+4 D