The process of sending back light rays which fall on the surface of an object, is called reflection of light. When a ray of light falls on a mirror at point , it is sent back by the mirror in another direction. Most of the objects reflect light which falls on them. Some objects reflect more light whereas other objects reflect less light.
The objects having polished, shining surfaces reflect more light than objects having unpolished, dull surfaces.
A shining silvered mirror reflects back almost all the light which falls on it. A table or chair having the surfaces reflect back only a small amount of light which falls on them. A black surface reflects almost no light.
A narrow beam of light is called a ray. A ray of light is represented by a straight line with an arrow head on it. The direction of this arrow shows the direction in which the light is traveling at that time. The narrow beam of light before reflection is called incident ray and after reflection is called reflected ray.
The light hitting the mirror is called the incident ray whereas the light leaving the mirror is called the reflected ray. A shiny surface reduces the absorption of light and causes the maximum reflection of light. An object which reflects light well is called a mirror. A highly polished and shiny metal object reflects light well and act as a mirror. Silver metal is one of the best reflector of light. Silver metal is used to make the glass mirrors which we use in our everyday life. The mirror which we use everyday are plane mirrors.
A plane mirror is a thin, flat and smooth sheet of glass having a shiny coating of silver metal on one side. The glass sheet of plane mirror offers a smooth surface. This smooth surface produces regular reflections and helps in forming a clear image. The silver metal coating makes the plane mirror shiny. The shiny surface of plane mirror gives us the maximum reflection of light. This helps in forming a bright image. The red paint behind the Silvered surface of plane mirrors reduces the transmission of light through the mirror and also protects the delicate silver coating of the mirror.
The reflection of light in a plane mirror takes place at the silvered surface inside it. A mirror reflects most of the light falling on it. Reflection of light in a plane mirror differs from reflection of light from other objects. The way light is reflected from a surface depends on whether the surface is rough or smooth.
Most of the objects have rough surfaces. Due to the rough surfaces, most of the objects reflect light in all direction. This is called irregular reflection. A piece of white paper reflects the light falling on it in all direction. 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. 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.
These mirrors often incorporate a mixture of concave and convex surfaces, or surfaces that gently change curvature, to produce bizarre, distorted reflections when people observe themselves. Spoons can be employed to simulate convex and concave mirrors, as illustrated in Figure 4 for the reflection of a young woman standing beside a wooden fence. When the image of the woman and fence are reflected from the outside bowl surface convex of the spoon, the image is upright, but distorted at the edges where the spoon curvature varies.
In contrast, when the reverse side of the spoon the inside bowl, or concave, surface is utilized to reflect the scene, the image of the woman and fence are inverted. The reflection patterns obtained from both concave and convex mirrors are presented in Figure 5. The concave mirror has a reflection surface that curves inward, resembling a portion of the interior of a sphere. When light rays that are parallel to the principal or optical axis reflect from the surface of a concave mirror in this case, light rays from the owl's feet , they converge on the focal point red dot in front of the mirror.
The distance from the reflecting surface to the focal point is known as the mirror's focal length. The size of the image depends upon the distance of the object from the mirror and its position with respect to the mirror surface. In this case, the owl is placed away from the center of curvature and the reflected image is upside down and positioned between the mirror's center of curvature and its focal point. The convex mirror has a reflecting surface that curves outward, resembling a portion of the exterior of a sphere.
Light rays parallel to the optical axis are reflected from the surface in a direction that diverges from the focal point, which is behind the mirror Figure 5. Images formed with convex mirrors are always right side up and reduced in size.
These images are also termed virtual images, because they occur where reflected rays appear to diverge from a focal point behind the mirror. The dashed line normal is perpendicular to the surface. All reflected light obeys the relationship that the angle of incidence equals the angle of reflection.
Just as images are reflected from the surface of a mirror, light reflected from a smooth water surface also produced a clear image. We call the reflection from a smooth, mirror-like surface specular as shown in Figure 2a.
When the surface of water is wind-blown and irregular, the rays of light are reflected in many directions. The law of reflection is still obeyed, but the incident rays Fig. Consequently, the outgoing rays are reflected at many different angles and the image is disrupted. Reflection from such a rough surface is called diffuse reflection and appears matte. In both cases the angle of incidence equals the angle of reflection at the point that the light ray strikes the surface.
Light is also reflected when it is incident on a surface or interface between two different materials such as the surface between air and water, or glass and water.
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