Question
Define lens and write its formula.

Answer

Any transparent medium surrounded by two surfaces, one of which or both surfaces are spherical is called lens. There are two types of lenses-(1) Convex lens (2) Concave lens.
The relationship between the distances of the object, the distance of the image and the focal length of the lens is called lens formula. i.e., $-\frac{1}{u}+\frac{1}{v}=\frac{1}{f}$.

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