In our ordinary experiences, light seems to behave as if it travels in straight lines until it strikes an object. Shadows cast by objects, the beam of light from a flashlight or a car’s headlights, the bright rays of sunlight through a clearing in the clouds, and the pencil-like laser light beams used in light shows all tell us that this is true (Figure 20.1 ). On the other hand, sound does not cast a “shadow;” you can be heard around sharp corners without a straight path to the listener. Radio and television waves also can be received without straight line paths to the radio or TV station antenna and as we have seen these are also forms of electromagnetic radiation just as is light. What distinguishes light in its ability to travel in straight lines is its small wavelength of about 5 × 10 –7 m, much smaller than any characteristic dimension of a typical object in its path. Sound, as well as radio and television EM waves, have wavelengths with macroscopic dimensions.
KeywordsCritical Angle Total Internal Reflection Plane Mirror Virtual Image Incident Intensity
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