Understanding the concept of Reflection and Refraction
The concept of Reflection and Refraction often put us in surprise. These concepts are the main reason that we see water on roads on a hot sunny day, and the reason that our mind commits a mistake in guessing the depth of water. This article will throw some light on the principles of reflection and refraction.
Aspirant Forum is thankful to the author for taking out some time and contributing this informative article.
Light is basically a form of energy which creates a sensation of vision to our eyes. Light can travel even in vacuum with a speed of around 3 × 108 ms-1. light has a dual nature which implies it exhibits both wave as well as particle nature. The wave nature of light can be explained using diffraction, interference and polarization while the particle nature of light is explained using reflection and refraction phenomena. The elementary particle of light is known as photon.
REFLECTION OF LIGHT
Reflection of light refers to bouncing back of light when it strikes an opaque surface. The phenomenon of reflection is similar to bouncing back of ball from a wall when it is thrown at some angle. We can see the objects around us only when they reflect the light falling on it into our eyes. In short, without light there is no sight. If all the lights of a room are turned off and all the windows are covered with black curtains then nothing is going to be visible. The appearance of black is merely a sign of the absence of light. Since the objects are not reflecting the light to our eyes nor generating the light and without light, there would be no sight.
LAWS OF REFLECTION
Reflection of light follows two simple laws which are also considered as laws of reflection of light.
The incident ray, reflected ray and normal at the point of incidence all lie in the same plane.
The angle of incidence is always equal to the angle of reflection.
REGULAR VS. DIFFUSED REFLECTION
Reflection of light rays from smooth surfaces like mirrors or a calm water surface leads to regular reflection while reflection of light rays from rough surfaces like wood, paper, asphalt roadway leads to diffused reflection.
APPLICATIONS OF REGULAR AND DIFFUSED REFLECTION
There are several interesting applications of this distinction between regular and diffuse reflection. One application pertains to the relative difficulty of night driving on a wet tarmac roadway compared to a dry tarmac roadway. Normally a roadway would cause diffuse reflection due to its rough surface but driving at night on a wet roadway results in an irritating glare from oncoming headlights. The glare is the result of the regular reflection of the light rays from an oncoming car. Another application of the distinction between diffuse and regular reflection pertains to the field of photography. The calm water provides for the regular reflection of light from the subject of the photograph. Since the light reflecting off the water undergoes regular reflection, the incident rays remain concentrated instead of diffusing.
REFRACTION OF LIGHT
Refraction of light involves a change in the direction of light rays as they pass from one medium to another. It is accompanied by a change in speed and wavelength of the light rays when light rays travel from one medium to another.
The amount of bending is determined by the fraction by which speed of light changes. The fraction by which speed of light changes with respect to its speed in vacuum is termed as refractive index of the medium.
LAWS OF REFRACTION AND SNELL’S LAW
The incident ray, refracted ray and normal at the point of incidence all lie in the same plane.
This law is also known as Snell’s law. It states that the ratio of sine of angle of incidence to the ratio of sine of angle of refraction is always constant for a particular medium.
i.e. sin i / sin r = Ƞ
Here, Ƞ is the refractive index
The greater the refractive index, the denser will be the medium and the greater will be bending of light rays.
APPLICATIONS OF REFRACTION OF LIGHT IN DAILY LIFE
Refraction of light can be observed in a number of phenomena in everyday life.
Nearly everyone must have observed or tried to touch something submerged in water. An object seen in the water usually appears to be at a different depth than it actually is, due to the refraction of light rays as they travel from the water into the air. The eyes and brain trace the light rays back into the water as if they have traveled from the object in a straight line and not refracted thereby creating a virtual image of the object that appears at a shallower depth.
- The pencil in water appears to be bent because light rays coming from the pencil are abruptly bent at the air-water interface before reaching our eyes.
Mirage: A Special case of Refraction
Refraction can also be observed in the form of mirage. . While driving down a road on a hot day, one may observe that there are pools of water up ahead, but by the time one approaches them, they disappear. In this case also light creates an optical illusion. Light waves travel faster through warm air than through cool air, and, thus, when the light enters the area over the heated surface of the asphalt, it experiences refraction. The waves are thus bent, creating the impression of a reflection, which suggests to the observer that there is water up ahead.
Even the human eye, rely in a fundamental way on the fact that light can be focused, refracted, and reflected. The refraction of light produces a wide variety of phenomena, including mirages, rainbows, apparent height of stars, twinkling of stars and curious optical illusions such as making fish appear to be swimming in more shallow water than they really are. Refraction also causes a thick-walled beer mug to appear fuller than it really is, and deceives us into thinking the sun is setting several minutes later than it really does. Millions of people use the power of refraction to correct faulty vision with eyeglasses and contact lenses, which enable them to see the world more clearly. By understanding these properties of light we are able to understand the magical world more clearly.
Courtesy: Ms. K. Thakur
former intern, National Physical Laboratory
Team Aspirant Forum