Chapter 11.pdf

11.2The Refraction of LightHere is a summary of what youwill learn in this section:• Refraction is the bending oflight as it passes betweenmedia that have differentrefractive indices.• Refraction occurs due to thechange in the speed of light indifferent media.• The index of refraction of amedium is the ratio of thespeed of light in a vacuumcompared to the speed of lightin the medium.• As light passes at an anglefrom a less dense medium intoa more dense medium, thelight ray bends toward thenormal.• Snell’s law relates the indicesof refraction of a medium to theangle of incidence andreflection.Figure 11.27 Laser light is transmitted along optical fibres for use in surgery.Fibre OpticsOne of the most important properties of light is that it tends to travel instraight lines. If you need light to bend around a corner or to shine intoa difficult-to-reach place, you might want to use optical fibres. Anoptical fibre is a thin, transparent glass tube that can transmit lighteven around corners (Figure 11.27). This is because the light in a fibreoptics tube cannot escape until it reaches the end of the tube.How does an optical fibre conduct a light ray around a corner?Imagine a long, curved tunnel whose walls, floor, and ceiling are linedwith mirrors. If you were to shine a laser beam into the tunnel, thebeam of light would change direction each time it reflected from amirror and would make it all the way to the end of the tunnel. This isexactly what happens on the inside of the optical fibre. The light rayreflects off the inside of the walls of the glass fibre. When the thin glassfibre bends around a corner, the light ray goes around the cornerthrough a series of reflections.434 UNIT D Light and Geometric Optics