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Question
An object lies at a distance of 2f from a concave lens of focal length f. Draw a ray-diagram to illustrate the image formation.
Solution
For a concave lens, when the object lies anywhere between the optical center (C) and infinity, the image is formed between the optical center (C) and the focus. Therefore, when the object is placed at 2f from the concave lens of focal length f, the image is formed between the optical center (C) and the focus (f). Also, the image formed is virtual, erect and diminished. The following ray diagram illustrates the image formed by the concave lens:
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