Question

# A point object O is placed at a distance of 20 cm from a convex lens of focal length 10 cm as shown in fig. At what distance x from the lens should a concave mirror of focal length 60 cm, be placed so that the final image coincides with the object?

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Solution

## Given that, Focal Length of convex lensf=10cm So, radius of curvaturer=20cm We know that, the object is placed at the radius of curvature So, the image is formed at the radius of curvature Now, The focal length of concave mirrorf=−60cm Image distancev=−20cm Now, using mirror formula 1f=1v+1u −160+120=1x x=30cm Hence, the distance is 30 cm

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