Q 12-09-211JEE MainJEE Main 2019 (12 Jan, Shift 2)Medium
Formation of real image using a biconvex lens is shown below. If the whole set up is immersed in water without disturbing the object and the screen positions, what will one observe on the screen?
Answer: (A) Image disappears
In water the focal length of a glass lens increases:
$$\frac{f_w}{f_a} = \frac{\mu_g - 1}{\mu_g/\mu_w - 1} = \frac{0.5}{1.5/1.33 - 1} \approx 4$$
The object, which was between $f$ and $2f$, is now well inside the new focal length, so the lens forms a virtual image on the object's side. No image is formed on the screen: the image disappears.
Solution by Sreeraj P, M.Sc Physics