Question

An object is placed at a distance of 20 cm from a convex mirror of radius of curvature convex cm. At what distance from the object should a plane mirror be placed so that the images due to the mirror and the plane mirror are on the same plane?

Answer 1

Focal length =` ("radius of curvature ")/2 = 40/2 = 20` cm
Object distance u =- 20 cm (from sign convention)
From mirror formula,

Distance between the object and the image is 20 + 10 = 30 cm.
Since for plane mirror object distance is equal to image distance, the plane mirror should be placed at a distance `30/2 = 15` cm from the object, for the image of the plane mirror and spherical mirror to be in the same plane.