# An object 4.8 cm tall is 38.0 cm from a concave lens. The resulting image is two-fifths as large as the object. What is the focal length of the lens?   cm

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An object 4.8 cm tall is 38.0 cm from a concave lens. The resulting image is two-fifths as large as the object. What is the focal length of the lens?   cm

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Step 1

Let us say that the object distance is ‘u’ and the image distance is ‘v’ from the optical centre of the lens. Also, the focal length of the lens is ‘f’. The formula of the lens is defined below:

Step 2

Now, the magnification is given as m = 2/5 and u = -38 cm. As, it is a concave lens, so, both image and object will be on the left-hand side thus, both v and u will be negative. So, the relation between ‘u’ and ‘v’ will be:

Step 3

Now, let us calculate t...

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