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?

The position of the final image formed by the given lens combination from the third lens will be at a distance of $\left(f_1=+10 \mathrm{cm}, f_2=-10 \mathrm{cm}\right.$ and$\left.f_3=+30 \mathrm{cm}\right)$

In the shown situation, if middle portion of the lens is painted black, then

The following figure shows a beam of light converging at point $P$. When a concave lens of focal length $16 \mathrm{cm}$ is introduced in the path of the beam at a place shown by dotted line such that $OP$ becomes the axis of the lens, the beam converges at a distance $x$ from the lens. The value of $x$ will be equal to