For example, if you look at a bird, light has reflected off that bird and travelled in nearly all directions. If some of that light enters your eyes, it hits the retina at the back of your eyes. An electrical signal is passed to your brain, and your brain interprets the signals as an image. The angle at which light hits a reflecting surface is called the angle of incidence, and the angle at which light bounces off a reflecting surface is called the angle of reflection.
If you measure the angle of incidence and the angle of reflection against the normal, the angle of incidence is exactly the same as the angle of reflection. With a flat mirror, it is easy to show that the angle of reflection is the same as the angle of incidence. Water is also a reflective surface.
When the water in a lake or sea is very still, the reflection of the landscape is perfect, because the reflecting surface is very flat. However, if there are ripples or waves in the water, the reflection becomes distorted. This is because the reflecting surface is no longer flat and may have humps and troughs caused by the wind. It is possible to make mirrors that behave like humps or troughs, and because of the different way they reflect light, they can be very useful.
Concave mirrors are used in certain types of astronomical telescopes called reflecting telescopes. The mirrors condense lots of light from faint sources in space onto a much smaller viewing area and allow the viewer to see far away objects and events in space that would be invisible to the naked eye. Light rays travel towards the mirror in a straight line and are reflected inwards to meet at a point called the focal point. Concave mirrors are useful for make-up mirrors because they can make things seem larger.
This concave shape is also useful for car headlights and satellite dishes. In this case, the parallel incident rays do not remain parallel after reflection, they are scattered in different directions.
It is also known as irregular reflection or scattering and so, takes place from rough surfaces like that of paper, cardboard, chalk, table, chair, walls and unpolished metal objects. Since, the angle of incidence and angle of reflection are different, the parallel rays of light falling on a rough surface go in different directions as explained below in the figure.
Before understanding the laws of reflection of light, lets understand the meaning of some important terms such as, incident ray, reflected ray, point of incidence, normal at the point of incidence , angle of incidence and angle of reflection. Incident ray: The ray of light falling on the surface of a mirror is called incident ray. Point of incidence: The point at which the incident ray falls on the mirror surface is called point of incidence. Reflected ray: The ray of light which is sent back by the mirror from the point of incidence is called reflected ray.
Normal: A line perpendicular or at the right angle to the mirror surface at the point of incidence is called normal. Angle of incidence: The angle made by the incident ray with the normal is called angle of incidence. Angle of reflection: The angle made by the reflected ray with the normal at point of incidence is called angle of reflection. The laws of reflection of light apply to both plane mirror as well as spherical mirror. In this article we will discuss about the images formed by the plane mirror.
First law of reflection: According to the first law, the incident ray, reflected ray and normal, all lie in the same plane. Second law of reflection: According to the second law, the angle of reflection is always equal to the angle of incidence. Also, it is important to note that when a ray of light falls normally on the surface of the mirror then the angle of incidence and the angle of reflection for such a ray of light will be zero.
This ray of light will be reflected back along the same path. Anything which gives out light with off its own of reflected by it is called an object. Most objects which reflect light are not smooth at the microscopic level.
Your clothing, the walls of most rooms, most flooring, skin, and even paper are all rough when viewed at the microscopic level. The picture at the right depicts a highly magnified, microscopic view of the surface of a sheet of paper. Reflection off of smooth surfaces such as mirrors or a calm body of water leads to a type of reflection known as specular reflection.
Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway leads to a type of reflection known as diffuse reflection. Whether the surface is microscopically rough or smooth has a tremendous impact upon the subsequent reflection of a beam of light.
The diagram below depicts two beams of light incident upon a rough and a smooth surface. A light beam can be thought of as a bundle of individual light rays which are traveling parallel to each other.
Each individual light ray of the bundle follows the law of reflection. If the bundle of light rays is incident upon a smooth surface, then the light rays reflect and remain concentrated in a bundle upon leaving the surface. On the other hand, if the surface is microscopically rough, the light rays will reflect and diffuse in many different directions.
For each type of reflection, each individual ray follows the law of reflection. However, the roughness of the material means that each individual ray meets a surface which has a different orientation. The normal line at the point of incidence is different for different rays. Subsequently, when the individual rays reflect off the rough surface according to the law of reflection, they scatter in different directions.
The result is that the rays of light are incident upon the surface in a concentrated bundle and are diffused upon reflection. The diagram below depicts this principle.
The normal line approximated at each point of incidence is shown in black and labeled with an N. In each case, the law of reflection is followed, resulting in five reflected rays labeled A , , B , , C , , D , , and E ,. There are several interesting applications of this distinction between specular and diffuse reflection.
One application pertains to the relative difficulty of night driving on a wet asphalt roadway compared to a dry asphalt roadway.
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