Question

Q. A circular disc of radius 10 cm is placed at a distance of 20 cm from the convex lens of focal length 10 cm as shown below the radius of image of disc is??
A)20 cm
B)10 cm
C)15 cm
D)5 cm


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Answer 1

Answer:

Explanation:

The convex lens and the convex mirror are shown in Figure.

The combination behaves like a concave mirror.

Let the distance of the object from the lens be x.

For the ray to retrace its path, it should be incident normally on the convex mirror, or in other words the rays shold pass through the center of curvature of the mirror.

From the diagram, we see that for the lens

u=−x,f=+20cm,v=+10+15=+25cm

From the lens equation, we get

1v−1u=1f or 125−1−x=120 or  x=100cm