A lens behaves as a converging lens in air and a diverging lens in water (u = 4/3). What will be the condition on the value of refractive index (u) of the material of the lens ?
If the refractive Index of a lens is less than the refractive index of the medium, it is immersed in , a converging lens will act as a diverging lesns and vice versa .
So if the RI of the converging lens is smaller than the RI of water ie. 4/3, then it will act as a diverging lens.