Refraction of light is a very common observable phenomenon. Here we shall discuss when and where does refraction occurs in a wave, telescope, human eye, glass, etc.
The bending of a light ray as it passes from one medium to another is known as the refraction of light. Refraction occurs because the speed of a wave is different in different media. When a light wave encounters a boundary of a medium, it changes direction, speed and transforms into a wave with a different wavelength.
The refraction of light is the reason behind several phenomena in our daily life. Stars appear to twinkle in the night sky due to the refraction of light as light has to travel through several layers of air (with different densities) to reach the human eye.
The pool water appears to be less in-depth than actual depth for a person observing the pool due to refraction. Refraction is one of the reasons behind the formation of a rainbow. Optical instruments like telescopes, camera, binoculars, etc., work by the principle of refraction. The cornea in the human eye refracts most of the light as it enters our eye.
We will explore more on this optical phenomenon and its occurrence in detail.
When does refraction occur in a wave?
A wave is a disturbance that transfers energy within a medium or from one medium to another without any transfer of particles. Refraction occurs in a wave when it is transmitted from one medium to another.
Whenever a wave encounters a different media, bending of the wave takes place. That is because; the speed of the travelling wave is different for different media. Any material, substance or space through which a wave travels is known as the medium. Refraction is not limited to light waves; it occurs in sound or water waves too. Air, water or glass are a few common examples of the medium through which light travels.
Refraction happens in all kinds of wave, like water wave or light wave. For instance a stick half immersed in water appears to be bent due to the refraction of light waves as speed of light wave is different in air and in water. Similarly, water waves move at different speed in shallow waters compared to deep waters.
Where does wave refraction occur?
Wave refraction occurs at the boundary of the two different media through which the wave passes. Refraction is a boundary phenomenon by which any wave would behave when it encounters a new medium or any obstacle in its path.
In the case of a light wave passing through a glass prism, refraction takes place at the boundary where the light wave enters the glass prism from air or vice versa. In the case of a water wave, as it propagates over different depths the speed of the wave changes and hence the direction of propagation of the wave changes i.e., refraction takes place.
Where in the telescope does refraction occur?
Telescope is an optical instrument that is used to view distant objects in the sky. Telescope deploys lenses to magnify smaller objects so that it is visible to the naked eye.
As the light from the distant object enters the lens of a telescope, refraction of the light wave takes place. That is because, the light from the distant object initially travelling through air enters lens, which is another medium. And as a result, the speed of light changes and hence refraction takes place. The curvature of lenses in a telescope is increased to aid for viewing the distant objects more clearly.
Where does refraction occur in the human eye?
Our vision relies on the ability of the eyes to refract light. Cornea and lens are the parts in the human eye where refraction takes place.
Most of the refraction occurs when light enters the curved clear surface of the eye called cornea. The lens also bends the light ray and aids for sharp vision. Even the tear film as well as the fluids inside our eye allows refraction for proper vision. Aqueous humor present inside our eye has a refractive index different from that of air hence the speed of light in both medium would be different.
Where does refraction occur in glass?
As we know, the speed of light is different in different media due to which each media has its own refractive index. Refractive index of glass is higher than that of air. Therefore a light ray either entering or leaving the glass medium gets refracted at the boundary separating the two media.
For example, let us consider a light ray travelling from air to a glass slab and then through the glass slab to air, as shown in the image below.
It can be seen that the light ray bends at the region where it encounters the boundary of the glass slab. Once it enters the glass medium, it traverses through the same path until it reached the next boundary where glass meets air. The light ray suffers refraction again and finally propagates through the air.
One of the most observable instance of refraction through glass is the when we place a glass slab over a written paper. The letters appear to be magnified if we read through the glass slab. This is due to the bending of light ray as it passes through the glass slab and then to our eye.
Frequently Asked Questions
What is refractive index?
Refractive index is a measure of bending of a light ray when it travels from one medium to another. Refractive index is the property of a material.
Refractive index is the ratio of speed of light in vacuum to the speed of light in the medium. Refractive index of air (or vacuum) is unity.