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Question
the image of an object by a lens is of magnification -1 . if the distance between the object and its image is 60cm what isthe focal length of the lens
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Solution
Hi,
Given,
Magnification of the lens, m = −1
This means image formed is real, inverted and of the same size as that of object. The mirror is concave mirror.
As we know concave mirror forms an image equal to the size of the object when object is placed at a distance twice the focal length of the lens. In such cases, distance of object and image from the lens is same. As given the distance between the object and its image is 60 cm. So, object is at a distance of 30 cm from the lens. Using the relation f = R/2. So, focal length of the lens is 15 cm.
Given,
Magnification of the lens, m = −1
This means image formed is real, inverted and of the same size as that of object. The mirror is concave mirror.
As we know concave mirror forms an image equal to the size of the object when object is placed at a distance twice the focal length of the lens. In such cases, distance of object and image from the lens is same. As given the distance between the object and its image is 60 cm. So, object is at a distance of 30 cm from the lens. Using the relation f = R/2. So, focal length of the lens is 15 cm.
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