A lens is a transparent optical device that uses refraction to focus or diverge light. The lens formula relates the object distance, image distance, a
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Why is the focal length of a convex lens positive and a concave lens negative?
By sign convention, focal lengths are positive if measured in the direction of light propagation (real focus for convex lenses) and negative if opposite (virtual focus for concave lenses).
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Can a concave lens produce a real image?
No, a concave lens always produces virtual, erect, and diminished images. It cannot converge light to form a real image.
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What is a diopter used for?
A diopter measures the optical power of a lens. Prescription lenses for glasses are usually specified in diopters. Higher diopter value means stronger lens and stronger correction needed.
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