A cylindrical vessel, whose diameter and height both are equal to 30 cm, is placed on a horizontal surface and a small particle P is placed in it at a distance of 5.0 cm from the center. An eye is placed at a position such that the edge of the bottom is just visible (see figure 18-E8). The particle P is in the plane of drawing. Up to what minimum height should water be poured in the vessel to make the particle P visible?
For the given cylindrical vessel;
Diameter (d) = 30cm
Radius (
) = 15 cm
Height (h) = 30 cm
d = height of water
The refractive index of water is 
1.33 =
By applying Snell’s law:
Angle of refraction = r =
(Point P will be visible when the angle of refraction becomes
)
Let, the distance from P to X be x cm.
----- (i)
Now, 
1