The focal length of convex mirror is 20 cm, an object is placed at the distance of 40 cm.
Answers
Given: An object is placed at a distance of 20 cm from a convex mirror or radius of curvature 40 cm.
To find the distance at which the plane mirror should be placed such that the images due to the mirror and the plane mirror are in the same plane
Solution:
According to the given criteria,
Object distance from convex mirror, u=−20cm
Radius of curvature of convex mirror, R=40cm
Focal length of the convex mirror, f= 2R
= 40/2
=20cm
Now applying the mirror formula we get, f1
= v1 + u1
⟹ 201
= v1 + −201
⟹ v1= 201+ 201
⟹v=10cm
So the distance is formed on the opposite side of the object at a distance of 10 cm from the mirror.
The distance between object and image is
u + v = 20+10=30cm
When plane mirror is placed in front of object and in order to get image at same position as convex mirror, the mirror should be place at
30/2 =15cm
As in plane mirror the object distance from mirror is equal to image distance from the plane mirror (refer above fig).
Hence the distance at which the plane mirror should be placed such that the images due to the mirror and the plane mirror are in the same plane = 15cm