Chapter 11.pdf

At a certain angle, called the critical angle, the refracted ray of lightfollows a path exactly along the surface of the water. Even though thelight refracts, it does not leave the water. In a way, the light is “trapped”inside the water (Figure 11.40).0°20°27°30°42°40°59°90°60° 60°air n 1.00water n 1.33Take It FurtherRefractive index has many uses,including identifying gemstones.It can also be used to find theconcentration of solutions. Findout about these and other uses ofthe refractive index. Begin yourresearch at ScienceSource.0°critical angle 48.8°light sourceFigure 11.40 When theangle of incidence is greaterthan the critical angle, totalinternal reflection occurs.What if the angle of the incident ray is increased even farther? Thelight ray is no longer refracted. Instead, it is completely reflected backinside the water. In an optical fibre, light is passed into the end of thefibre at an angle greater than the critical angle. Because the fibre is madeof glass, which has a higher index of refraction than the surroundingmedium, the light ray is completely reflected inside the fibre.Suggested Activity •D20 Design a Lab on page 446MiragesBoth total internal reflection and refraction play a role in forming amirage (Figure 11.41). A mirage is an image of a distant objectproduced as light refracts through air of different densities(Figure 11.42). Since the light rays pass through layers of air withprogressively lower indices of refraction, eventually the light is totallyinternally reflected.light rayfrom skylight rayfrom cloudobservercloudless dense, hot airmore dense, cool airhot pavementFigure 11.41 What looks like apuddle of water from the distance isactually an image of the sky that isproduced as light from the sky is bentnear the surface of the road up intothe eyes of the observer.image of cloudFigure 11.42 Light from an object in the sky is refracted due to the difference in density of theair above the pavement compared with the air higher up.Ray diagrams model the behaviour of light in mirrors and lenses.443