Some effects of refraction
The apparent upward bending of a stick when placed in water is shown in Fig. 23.6. Rays of light from the end B of the stick pass from water to air, and are bent away from the normal, since they are passing to a less optically dense medium. Entering the eye, the rays appear to be coming from a point C above B. C is thus the image of
B as a result of refraction. The same reasoning applies to any point on the immersed portion of the stick AB, so that the observer sees an image apparently in the position AC. To avoid confusion in this and similar ray diagrams one should always be careful to use the accepted convention of drawing real rays, real images and objects in full lines, and virtual rays and images in dotted lines. In addition, an arrow should be placed on a ray to show the direction in which the light travels. Fig. 23.7 illustrates the appearance of print viewed through the top of a piece of thick glass placed over it. Since the rays are refracted away from the normal when they pass from glass to air, the print and the bottom of the glass appear raised. The apparent raising of the print thus occurs for the same reason that a stick appears to be bent upwards when placed in water, as explained above.