The correct option is C 20 cm
behind the concave mirror
The distance of object from the convex lens, u=−20 cm
Height of image, h=5 cm
Focal length of convex lens, f1=10 cm
Focal length of concave mirror, f2=−20 cm
(Assuming new cartesian sign convention)
Distance between the mirror and the lens, d=30 cm
By lens formula, 1f=1v−1u 110=1v−1−20 cm v=20 cm
The positive sign show that the image is formed to the right side of the lens.
The image v
in front of concave mirror, between pole and focus acts as an object for the concave mirror.
Hence, the object distance from concave mirror, u′=−10 cm
By mirror formula, 1f2=1v′+1u′ 1−20=1v′+1−10 v′=20 cm
The image formed by concave mirror is 20 cm
behind the mirror.