Formation of real image using a biconvex lens is shown below: If the… | JEE Main 2019 (12 Jan, Shift 2)

Q91JEE Main 2019 · 12 JAN · SHIFT 2Medium

Spherical Surfaces & Thin Lenses

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?

Show answer and solution

Answer: (a)

In water: $\frac{f_w}{f_a} = \frac{0.5}{\frac{1.5}{1.33} - 1} \approx 4$ , so the focal length becomes about $4f$ .
The object (between $f$ and $2f$ ) is now inside the new focal length, so no real image is formed at the screen.
So the answer is (a) image disappears.

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