Question

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.

(i) What should be the range of distance of an object placed in front of the mirror ?

(ii) Will the image be smaller or larger than the object. Draw a ray diagram to show the formation of image in this case.

(iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror? Draw ray a diagram for this situation to justify your answer.

Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.

Answer 1

(i) Inorder to obtain an erect image of the object, the object should be between the pole and the focus. Therefore, the range of distance should be 0 cm to less than 12 cm from the mirror.

(ii) The image will be larger than the object.

(iii) Radius of curvature is the distance between centre of curvature and pole.
We know, $radiusofcurvature=2\times focallength$.
Given, focal length = 12 cm, therefore, here radius of curvature $=2\times 12=24cm$. As the object is placed at 24 cm, hence the object is placed at the centre of curvature (C).
We know when object is placed at C, the image also will be at C.
So, image will be formed at a distance of 24 cm in front of the mirror.