A point source of light is kept at a depth of h in water of refractive index 4/3. The radius of the circle at the surface of water through which light emits is

Three identical convex lenses each of focal length $$\mathrm{f}$$ are placed in a straight line separated by a distance $$\mathrm{f}$$ from each other. An object is located at f/2 in front of the leftmost lens. Then,

The human eye has an approximate angular resolution of $$\theta$$ = 5.8 $$\times$$ 10^$$-$$4 rad and typical photo printer prints a minimum of 300 dpi (dots per inch, 1 inch = 2.54 cm). At what minimal distance d should a printed page be held so that one does not see the individual dots?