When light waves are incident on a smooth, flat surface, they reflect away from the surface at the same angle as they arrive. This tutorial explores the relationship between incident and reflected angles for a virtual sinusoidal light wave. Because light behaves in some ways as a wave and in other ways as if it were composed of particles, several independent theories of light reflection have emerged.
According to wave-based theories, the light waves spread out from the source in all directions, and upon striking a mirror, are reflected at an angle determined by the angle at which the light arrives. The reflection process inverts each wave back-to-front, which is why a reverse image is observed.
The shape of light waves depends upon the size of the light source and how far the waves have traveled to reach the mirror. Wavefronts that originate from a source near the mirror will be highly curved, while those emitted by distant light sources will be almost linear, a factor that will affect the angle of reflection. According to particle theory, which differs in some important details from the wave concept, light arrives at the mirror in the form of a stream of tiny particles, termed photons, which bounce away from the surface upon impact.
Because the particles are so small, they travel very close together virtually side by side and bounce from different points, so their order is reversed by the reflection process, producing a mirror image. Regardless of whether light is acting as particles or waves, however, the result of reflection is the same. The reflected light produces a mirror image.
The amount of light reflected by an object, and how it is reflected, is highly dependent upon the degree of smoothness or texture of the surface. When surface imperfections are smaller than the wavelength of the incident light as in the case of a mirror , virtually all of the light is reflected equally. However, in the real world most objects have convoluted surfaces that exhibit a diffuse reflection, with the incident light being reflected in all directions.
Many of the objects that we casually view every day people, cars, houses, animals, trees, etc. For instance, an apple appears a shiny red color because it has a relatively smooth surface that reflects red light and absorbs other non-red such as green, blue, and yellow wavelengths of light. The reflection of light can be roughly categorized into two types of reflection. Specular reflection is defined as light reflected from a smooth surface at a definite angle, whereas diffuse reflection is produced by rough surfaces that tend to reflect light in all directions as illustrated in Figure 3.
There are far more occurrences of diffuse reflection than specular reflection in our everyday environment. The amount of light reflected by an object, and how it is reflected, is very dependent upon the smoothness or texture of the surface. This interactive tutorial investigates variations in reflectivity of surfaces as they transition from smooth, mirror-like textures to very rough and irregular.
To visualize the differences between specular and diffuse reflection, consider two very different surfaces: a smooth mirror and a rough reddish surface. The mirror reflects all of the components of white light such as red, green, and blue wavelengths almost equally and the reflected specular light follows a trajectory having the same angle from the normal as the incident light.
The rough reddish surface, however, does not reflect all wavelengths because it absorbs most of the blue and green components, and reflects the red light. Also, the diffuse light that is reflected from the rough surface is scattered in all directions. Perhaps the best example of specular reflection, which we encounter on a daily basis, is the mirror image produced by a household mirror that people might use many times a day to view their appearance.
The mirror's smooth reflective glass surface renders a virtual image of the observer from the light that is reflected directly back into the eyes. This image is referred to as "virtual" because it does not actually exist no light is produced and appears to be behind the plane of the mirror due to an assumption that the brain naturally makes.
The way in which this occurs is easiest to visualize when looking at the reflection of an object placed on one side of the observer, so that the light from the object strikes the mirror at an angle and is reflected at an equal angle to the viewer's eyes. As the eyes receive the reflected rays, the brain assumes that the light rays have reached the eyes in a direct straight path.
Tracing the rays backward toward the mirror, the brain perceives an image that is positioned behind the mirror. An interesting feature of this reflection artifact is that the image of an object being observed appears to be the same distance behind the plane of the mirror as the actual object is in front of the mirror.
The type of reflection that is seen in a mirror depends upon the mirror's shape and, in some cases, how far away from the mirror the object being reflected is positioned.
Mirrors are not always flat and can be produced in a variety of configurations that provide interesting and useful reflection characteristics. Concave mirrors , commonly found in the largest optical telescopes, are used to collect the faint light emitted from very distant stars.
The curved surface concentrates parallel rays from a great distance into a single point for enhanced intensity. This mirror design is also commonly found in shaving or cosmetic mirrors where the reflected light produces a magnified image of the face.
The inside of a shiny spoon is a common example of a concave mirror surface, and can be used to demonstrate some properties of this mirror type. If the inside of the spoon is held close to the eye, a magnified upright view of the eye will be seen in this case the eye is closer than the focal point of the mirror.
If the spoon is moved farther away, a demagnified upside-down view of the whole face will be seen. Here the image is inverted because it is formed after the reflected rays have crossed the focal point of the mirror surface. Another common mirror having a curved-surface, the convex mirror, is often used in automobile rear-view reflector applications where the outward mirror curvature produces a smaller, more panoramic view of events occurring behind the vehicle.
When parallel rays strike the surface of a convex mirror, the light waves are reflected outward so that they diverge. When the brain retraces the rays, they appear to come from behind the mirror where they would converge, producing a smaller upright image the image is upright since the virtual image is formed before the rays have crossed the focal point.
Convex mirrors are also used as wide-angle mirrors in hallways and businesses for security and safety.
The most amusing applications for curved mirrors are the novelty mirrors found at state fairs, carnivals, and fun houses. Refraction is when light waves change direction as they pass from one medium to another. Light travels slower in air than in a vacuum, and even slower in water. As light travels into a different medium, the change in speed bends the light. Different wavelengths of light are slowed at different rates, which causes them to bend at different angles.
Wave Behaviors. Retrieved [insert date - e. Science Mission Directorate. National Aeronautics and Space Administration. Wave Behaviors Light waves across the electromagnetic spectrum behave in similar ways. For example, when the full spectrum of visible light travels through the glass of a prism, the wavelengths are separated into the colors of the rainbow.
Electromagnetic Spectrum Series Series Homepage. Infrared Waves. Reflected Near-Infrared. Visible Light. Ultraviolet Waves. Earth's Radiation Budget. Diagram of the Electromagnetic Spectrum.
Recommended Articles. September 24, Solar Eclipse - June 10, June 09, Refraction Refraction is the change in direction of propagation of a wave when the wave passes from one medium into another, and changes its speed.
Light waves are refracted when crossing the boundary from one transparent medium into another because the speed of light is different in different media.
Assume that light waves encounter the plane surface of a piece of glass after traveling initially through air as shown in the figure to the right. What happens to the waves as they pass into the glass and continue to travel through the glass? The speed of light in glass or water is less than the speed of light in a vacuum or air.
Typical values for the index of refraction of glass are between 1. The distance between wave fronts will therefore be shorter in the glass than in air, since the waves travel a smaller distance per period T. Now consider wave fronts and their corresponding light rays approaching the surface at an angle. We can see that the rays will bend as the wave passes from air to glass.
The bending occurs because the wave fronts do not travel as far in one cycle in the glass as they do in air. As the diagram shows, the wave front halfway into the glass travels a smaller distance in glass than it does in air, causing it to bend in the middle. Thus, the ray, which is perpendicular to the wave front, also bends. The situation is like a marching band marching onto a muddy field at an angle to the edge of the field.
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