Q25. HOTS What change do you expect in the focal length of a concave mirror and a convex lens, when immersed in water?
Sol. There is no change in the focal length of concave mirror because it is about half of its radius of curvature and has nothing to do with the external medium.
However, the focal length of convex lens increase because refractive index of glass with respect to water is less than refractive index of glass with respect to air.