A mirror, on the other hand, has a smooth surface compared with the wavelength of light and reflects light at specific angles, as illustrated in Figure b.
When the Moon reflects from a lake, as shown in Figure c , a combination of these effects takes place. Only the observer at a particular angle sees the reflected light. We see the light coming from a direction determined by the law of reflection. The angles are such that the image is exactly the same distance behind the mirror as you stand in front of the mirror. If the mirror is on the wall of a room, the images in it are all behind the mirror, which can make the room seem bigger.
Although these mirror images make objects appear to be where they cannot be like behind a solid wall , the images are not figments of your imagination. Mirror images can be photographed and videotaped by instruments and look just as they do with our eyes which are optical instruments themselves.
The precise manner in which images are formed by mirrors and lenses is discussed in an upcoming chapter on Geometric Optics and Image Formation. Corner Reflectors Retroreflectors A light ray that strikes an object consisting of two mutually perpendicular reflecting surfaces is reflected back exactly parallel to the direction from which it came Figure. This is true whenever the reflecting surfaces are perpendicular, and it is independent of the angle of incidence.
For proof, see Figure at the end of this section. Such an object is called a corner reflector , since the light bounces from its inside corner. Corner reflectors are a subclass of retroreflectors, which all reflect rays back in the directions from which they came. Although the geometry of the proof is much more complex, corner reflectors can also be built with three mutually perpendicular reflecting surfaces and are useful in three-dimensional applications.
Many inexpensive reflector buttons on bicycles, cars, and warning signs have corner reflectors designed to return light in the direction from which it originated. The Apollo astronauts placed a true corner reflector on the Moon Figure. Laser signals from Earth can be bounced from that corner reflector to measure the gradually increasing distance to the Moon of a few centimeters per year.
Working on the same principle as these optical reflectors, corner reflectors are routinely used as radar reflectors Figure for radio-frequency applications. Figure 6. Our image in a mirror is behind the mirror. The two rays shown are those that strike the mirror at just the correct angles to be reflected into the eyes of the person.
The image appears to be in the direction the rays are coming from when they enter the eyes. Take a piece of paper and shine a flashlight at an angle at the paper, as shown in Figure 3. Now shine the flashlight at a mirror at an angle. Do your observations confirm the predictions in Figure 3 and Figure 4? Shine the flashlight on various surfaces and determine whether the reflected light is diffuse or not. You can choose a shiny metallic lid of a pot or your skin. Using the mirror and flashlight, can you confirm the law of reflection?
You will need to draw lines on a piece of paper showing the incident and reflected rays. This part works even better if you use a laser pencil. Figure 7. A corner reflector sends the reflected ray back in a direction parallel to the incident ray, independent of incoming direction. Figure 8. A flat mirror neither converges nor diverges light rays. Two rays continue to diverge at the same angle after reflection. Skip to main content. The glare is the result of the specular reflection of the beam of light from an oncoming car.
Normally a roadway would cause diffuse reflection due to its rough surface. But if the surface is wet, water can fill in the crevices and smooth out the surface. Rays of light from the beam of an oncoming car hit this smooth surface, undergo specular reflection and remain concentrated in a beam. The driver perceives an annoying glare caused by this concentrated beam of reflected light. A second application of the distinction between diffuse and specular reflection pertains to the field of photography.
Many people have witnessed in person or have seen a photograph of a beautiful nature scene captured by a photographer who set up the shot with a calm body of water in the foreground. The water if calm provides for the specular reflection of light from the subject of the photograph. Light from the subject can reach the camera lens directly or it can take a longer path in which it reflects off the water before traveling to the lens.
Since the light reflecting off the water undergoes specular reflection, the incident rays remain concentrated instead of diffusing. The light is thus able to travel together to the lens of the camera and produce an image an exact replica of the subject which is strong enough to perceive in the photograph.
An example of such a photograph is shown below. If a bundle of parallel incident rays undergoing diffuse reflection follow the law of reflection, then why do they scatter in many different directions after reflecting off a surface? Each individual ray strikes a surface which has a different orientation.
Since the normal is different for each ray of light, the direction of the reflected ray will also be different. Perhaps you have observed magazines which have glossy pages. The usual microscopically rough surface of paper has been filled in with a glossy substance to give the pages of the magazine a smooth surface. Do you suppose that it would be easier to read from rough pages or glossy pages? Explain your answer. It is much easier to read from rough pages which provide for diffuse reflection.
Glossy pages result in specular reflection and cause a glare.
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