If the refractive index from air to glass is $$\frac{3}{2}$$ and that from air to water is $$\frac{4}{3}$$, then the ratio of focal lengths of a glass lens in water and in air is

Two thin biconvex lenses have focal lengths $$f_1$$ and $$f_2$$. A third thin biconcave lens has focal length of $$f_3$$. If the two biconvex lenses are in contact, then the total power of the lenses is $$P_1$$. If the first convex lens is in contact with the third lens, then the total power is $$P_2$$. If the second lens is in contact with the third lens, the total power is $$P_3$$, then

The size of the image of an object, which is at infinity, as formed by a convex lens of focal length $$30 \mathrm{~cm}$$ is $$2 \mathrm{~cm}$$. If a concave lens of focal length $$20 \mathrm{~cm}$$ is placed between the convex lens and the image at a distance of $$26 \mathrm{~cm}$$ from the lens, the new size of the image is

An object approaches a convergent lens from the left of the lens with a uniform speed $$5 \mathrm{~m} / \mathrm{s}$$ and stops at the focus, the image