Formation of real image using a biconvex lens is shown below: If the whole setup is immersed in water without disturbing the object and the screen position, what will one observe on the screen?

From 1/f = (μrel - 1)(1/R1 - 1/R2)

The focal length of a lens depends on the refractive index of the lens material relative to the surrounding medium. When the setup is immersed in water, the relative refractive index of the lens material with respect to water decreases. This results in an increase in the focal length of the biconvex lens. Since the object and screen positions remain unchanged, the new image will not form on the screen, leading to the disappearance of the image. Therefore, one will observe that the image disappears from the screen.