Question

focal length of convex len when immersed in water

Answer 1

This is because the focal length of mirrors does not depend on the external medium in which it is held. In case of lenses, refraction takes place. When a lens is immersed in water, the value of refractive index decreases. Hence its focal length increases.

Answer 2

when a convex lens is immersed in water then its focal length is increased. because the refractive index is decreased ...

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