![]() ![]() To his disappointment, Snell never discovered the reason for this refraction effect. The stick in water appears to be bent because light rays reflected from the stick are abruptly bent at the air-water interface before reaching our eyes. ![]() In effect, the more a substance is able to bend or refract light, the larger its refractive index value is said to be. During the 1600s, the Dutch mathematician Willebrord Snell succeeded in developing a law that defined a value related to the ratio of the incident and refracted angles, which has subsequently been termed the bending power or refractive index of a substance. Light waves coming from the sides (front and back) of the straw are shifted to a greater degree than those coming from the center of the straw, making it appear larger than it really is.Īs early as the first century (A.D.), the ancient Greek astronomer and geographer Ptolemy attempted to mathematically explain the amount of bending (or refraction) that occurred, but his proposed law was later determined to be unreliable. The waves must first pass through the water, then through the glass/water boundary and finally through the air. The straw in Figure 2 appears magnified and slightly distorted due to refraction of reflected light waves from the surface of the straw. Light is refracted when it leaves water, giving rise to the illusion that objects in water appear to be both distorted and closer than they really are. When a straight pole or stick is partially submerged in water, the pole no longer appears straight, but slants off at a different angle or direction (see Figure 2 for an illustration of this effect with a soda straw in a glass of water). Early scientists realized that the ratio between the angle at which light crosses the media interface and the angle produced after refraction is a very precise characteristic of the material producing the refraction effect.įor centuries, man had noticed a rather odd, but obvious fact. If the angle of the beam is increased even farther, the light will refract with increasing proportion to the entry angle. ![]() As an example, a beam of light striking water vertically will not be refracted, but if the beam enters the water at a slight angle it will be refracted to a very small degree. However, if the light impacts the boundary at any other angle it will be bent or refracted, with the degree of refraction increasing as the beam is progressively inclined at a greater angle with respect to the boundary. Condensing or collecting lenses are also utilized in modern microscopes and other optical instruments to concentrate light, relying on the same principles of refraction as did the early lacemaker's condenser.Īs light passes from one substance into another, it will travel straight through with no change of direction when crossing the boundary between the two substances head-on (perpendicular, or a 90-degree angle of incidence). The curved surface of the glass sphere functions as a large collecting surface for the light rays, which are then refracted toward a common focal point in a manner similar to that of a convex lens. Figure 1 illustrates a lacemaker's condenser made in the 1800s, which consists of several glass spheres arranged in a circle around a candle stand, enabling light from the candle to be focused or concentrated into several bright spots. Early nineteenth century lacemakers relied on water-filled glass spheres to focus or condense candlelight onto small areas of their work in order to help them see fine details more clearly. ![]()
0 Comments
Leave a Reply. |