There are a host of medical diagnostic and therapeutic uses. Samples can also be obtained, such as by lassoing an intestinal polyp for external examination.įiber optics has revolutionized surgical techniques and observations within the body. Surgery can be performed, such as arthroscopic surgery on the knee joint, employing cutting tools attached to and observed with the endoscope. Light is transmitted down one fiber bundle to illuminate internal parts, and the reflected light is transmitted back out through another to be observed. Endoscopes are used to explore the body through various orifices or minor incisions. The output of a device called an endoscope is shown in Figure 25.15(b). Such rays continue down the fiber, even following it around corners, since the angles of reflection and incidence remain large.īundles of fibers can be used to transmit an image without a lens, as illustrated in Figure 25.15. Rays are reflected around corners as shown, making the fibers into tiny light pipes.įigure 25.14 Light entering a thin fiber may strike the inside surface at large or grazing angles and is completely reflected if these angles exceed the critical angle. In fact, most fibers have a varying refractive index to allow more light to be guided along the fiber through total internal refraction. Because the fibers are thin, light entering one is likely to strike the inside surface at an angle greater than the critical angle and, thus, be totally reflected (See Figure 25.14.) The index of refraction outside the fiber must be smaller than inside, a condition that is easily satisfied by coating the outside of the fiber with a material having an appropriate refractive index. Fiber optics employs the transmission of light down fibers of plastic or glass.
Internal reflection definition tv#
In communications, it is used to transmit telephone, internet, and cable TV signals. Fiber Optics: Endoscopes to Telephonesįiber optics is one application of total internal reflection that is in wide use. A number of interesting applications of total internal reflection follow. There is no total reflection for rays going in the other direction-for example, from air to water-since the condition that the second medium must have a smaller index of refraction is not satisfied. 4º, and that from flint glass to crown glass is 66. 6º, while that from diamond to air is 24. The same calculation as made here shows that the critical angle for a ray going from water to air is 48. Different combinations of materials have different critical angles, but any combination with n 1 > n 2 n 1 > n 2 can produce total internal reflection. This will make the inside surface of the clear plastic a perfect mirror for such rays without any need for the silvering used on common mirrors.
This means that any ray of light inside the plastic that strikes the surface at an angle greater than 42.2º 42.2º will be totally reflected. If the incident angle θ 1 θ 1 is greater than the critical angle, as shown in Figure 25.13(c), then all of the light is reflected back into medium 1, a condition called total internal reflection. That is, θ c θ c is the incident angle for which θ 2 = 90º θ 2 = 90º. The largest the angle of refraction θ 2 θ 2 can be is 90º 90º, as shown in Figure 25.13(b).The critical angle θ c θ c for a combination of materials is defined to be the incident angle θ 1 θ 1 that produces an angle of refraction of 90º 90º. (Since n 1 > n 2 n 1 > n 2, the angle of refraction is greater than the angle of incidence-that is, θ 2 > θ 1 θ 2 > θ 1.) Now imagine what happens as the incident angle is increased. If, as shown in the figure, the index of refraction for the second medium is less than for the first, the ray bends away from the perpendicular. Part of the light crosses the boundary and is refracted the rest is reflected. Interestingly, we can produce total reflection using an aspect of refraction.Ĭonsider what happens when a ray of light strikes the surface between two materials, such as is shown in Figure 25.13(a). But it would be useful to have a mirror that reflects all of the light that falls on it.
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