Q25. 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 the object distance in the above case?
(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?
Answers
i. When an object is kept in front of the Focus of a concave mirror, an erect image is formed. The focal length that is the distance between the Focus and pole of the concave mirror is given 12 cm. So the range of the object distance must be less than 12 cm.
ii. The image would be enlarged that is it would be larger than the object.
Consider the image given above for the ray diagram.AB is the object and the image is A' B' formed on the other side of the mirror.
iii. Distance between the centre of curvature and the Focus is same as the distance between the Focus and the pole. So the center of curvature is at a distance of 12+12 cm that is 24 cm. According to the question the object is placed 24 cm in front of the mirror. So, the object is placed at the Centre of curvature.
When object is placed at C the image is formed at
the same position that is at the centre of curvature. Consider the second ray diagram.
Tap on the image to view the full image.
Hope this helps...
