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A CONVEX LENS IS PLACED IN WATER.ITS FOCAL LENGTH WILL________________.
Increases.Water's refractive index is in between air's and glass's. Therefore there is smaller change in refractive index between water and glass than between air and glass. Therefore, when the lens is put in water, then the light ray is bent by smaller amount after refraction. Therefore the ray travels for longer distance before it meets the principal axis. In other words focal length is larger.


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