A Rod Of Length 10 Cm Lies Along The Principal Axis Of A Concave Mirror Of Focal Length 10 Cm In Such A Way That The End Closer To The Pole Is 20 Cm Away From It. Find The Length Of The Image

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Question

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that the end closer to the pole is 20 cm away from it. Find the length of the image

diffcult

Solution

Correct option is

5.0 cm

The situation is shown in figure. The radius of curvature of the mirror is r= 2f = 20 cm. Thus, the nearer end B of the rod AB is at the centre of the curvature and hence, its image will be formed at B itself.

We shell now locate the image of A.

Here u = –30 cm and f = –10 cm. We have

Thus, the image of A is formed at 15 cm from the pole. The length of the image is, 5.0 cm.

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