Question

a point object is placed at a distance of 30 cm from the convex lens of focal length 20cm at what distance from the lens convex mirror of focal length 10cm should be placed so that the final image is formed at the object itself

Answer 1

Answer:

Explanation:

Just to be different, let’s answer using Newton’s lens law: XX’=f^2

So X is the distance from the object to the front focal point, X’ is from the rear focal point to the image. Then

X = 20–10 = 10.

X’ = f^2/X = 10^2/10 =10

The lens to image distance is f + X’ = 10+ 10 =20 cm