When successive layers of air have different temperatures, the ability of sound to travel faster in warm air than in cold air causes bending of sound. This bending of sound is called refraction.
On a warm day, the air near the ground is warmer than the air above and so the speed of sound waves near the ground is higher. This causes the bending of the sound away from the ground. On a cold day or at night, the reverse happens and the sound waves bend towards the earth. Thus on a cold day sounds can be heard over longer distances.
Sounds can be heard at abnormally long distances over water on quiet days. This happens because air next to water is cooler than air above and, therefore, sound waves bend towards the water and can travel long distances.
Light bends when it passes obliquely from one medium to another. This is called refraction of light. When a ray passes from one medium to another optically denser medium, e.g. from air to water or glass, it bends towards the normal. Conversely, a ray passing from water or glass into air is bent away from the normal. Light that enters another medium along the normal, however, does not bend.
The explanation for the bending lies in the different speeds of the light in media of different densities. The speed of light in vacuum, denoted by c, is nearly 3 x (10 to the power 8)m/s. In air the speed of light is slightly (0.03%) less than c. The speed in water is nearly 0.75c and in glass it is nearly 0.66c. The refractive index of a medium = speed of light in vacuum / speed of light in the medium.
When the sound waves enter from one medium to the other medium having different densities then the waves change their path. This bending of sound waves is known as refraction. Refraction is considered as a very important phenomenon for the transmission of sound waves from one origin to the other. The application of sound waves come when air above the earth is warmer as compare to air on earth surface. In such situation sound will be bent back downward toward the surface of the earth because of refraction of sound waves.
The term refraction is a noun that is usually used in reference to the turning or bending of waves, (a sound or light wave, for instance) as it passes through from one medium to another medium which has a different optical density. In the field of astronomy refraction refers to an apparent alteration in the position of celestial objects, which results from the bending of rays of light that enter the Earth's atmosphere.
It takes on different meanings in the field of medicine where it could refer to the ability that eyes have to bend light such that a given image comes to a focus on the retina. It could also mean determination of the refractive qualities of the eye.
The adjective forms of the word refraction are refractional and refractive. The adverb form of the word is refractively; while the noun forms of the same are refractiveness and refractivity.
