The Human Eye and the Colourful World

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Introduction

Let us discuss the concept, the human eye, and the colorful world in brief. The human eye, an organ that allows vision and reacts to light. The Rod and Cone cells present in the retina allow vision and conscious light perception, including the perception of depth and color differentiation. The human eye is possibly capable of detecting a single photon and can differentiate between about 10 million colors. The eye is the sensory nervous system part.

The human eye's non-image-forming photosensitive ganglion cells in the retina similar to other mammals' eyes, receive light signals which affect the adjustment of the size of the pupil, suppression, and entrainment of the body clock and regulation of the hormone melatonin.

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It is a naturally occurring optical body element as we know that we have a pair of eyes, and its function is to allow us to notice. Without that part, the whole world would have been a dark place for us.

Structure of a Human Eye

  • It is a circular or spherical ball with a small bulge on the front

  • It is located in the socket of the eye

  • It has two layers that cover it which are, scleroid and choroid

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Function of Scleroid

Scleroid is the outermost covering layer that consists of white fibres, and its functionality is to protect all parts of the eye.

Function of Choroid

The choroid is a grey membrane that is attached to a choroid from the inner side. Its functionality is to darken the eye from inside. So, no internal reflection takes place.

Eye Defects

Let us have a look at a few eye defects that occur very generally for more human beings.

Myopia (Short-Sightedness)

In this defect, a person unable to see far objects clearly whereas can see the nearby objects. This is because the ciliary muscles don't relax, and the lens doesn't elongate properly because of which the focal length does not properly increase. Resultantly no clear image is formed.

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Defect on Eyes

Eyeball, as being too elongated, the converging lens power is also too high. Because of this, the image is formed in front of the retina, and the brain cannot identify it. It can overcome using spectacles containing a concave lens that diverges the rays first. Then, our (the human) eye lens can converge them on the retina properly.

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Hypermetropia (Long-Sightedness)

In this defect, a person is unable to see nearby objects but can clearly see the far off objects. This is because the ciliary muscles don't contract properly, the lens doesn't become thick and short because of which the focal length doesn't decrease. Resultantly, the image formed is not clear, and the brain can't identify it.

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Defect on Eye

Eyeballs being converging power and too short of the lens is too low. Due to this, the image forms behind the retina. It can be overcome by using spectacles containing a convex lens that increases the ciliary power of the eye lens. So that it can converge rays on the retina properly.

Refraction through Prism

Prism

Prism is a piece of any transparent material or a piece of glass bonded by a triangular and three rectangular surfaces. The rectangular surfaces are referred to as refracting surfaces. Where the angle between two refracting surfaces is called the angle of the prism or refracting angle.

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The line along where the two refracting surfaces meet is referred to as refracting the edge. Any of the prism sections that are perpendicular to the refracting edge is called the principal section of the edge.

The refraction via glass prism and glass slab differences can be given below.

The emergent ray lies parallel to the incident ray in the slab but considering a prism, the emergent ray won't be parallel to the incident ray due to the opposite faces of the prism eye are not parallel to one other.

Dispersion

It is the phenomenon of splitting light into seven colors. When light (Sunlight or bulb light) is allowed to pass via glass prism, it splits into seven colors. It happens because we know white light is a combination of seven colours and on entering the prism, each colour gets refracted by different angles because of which different colour (spectrum) is obtained on the screen.

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The obtained colours are Red, Orange, Yellow, Green, Blue, Indigo, Violet.

The human eye the colourful world, can be obtained by the below explained colors, which are a part of the spectrum.

  • In red color, wavelength decreases and frequency increases

  • Red color - Least Deviated

  • Violet color- Maximum Deviated

  • All seven colours can recombine to produce white light

An application of dispersion is the formation of a Rainbow.

Rainbow

It is an example of dispersion (Spectrum produced by the dispersion of sunlight). "It is formed by the dispersion of white sunlight by the raindrops that are present in the atmosphere.” Each and every raindrop acts as a tiny glass prism. Rainbow is always formed opposite the sun. White light enters these raindrops. Different coloured rays are refracted through different angles where the rainbow is formed thus.

FAQ (Frequently Asked Questions)

1. Explain Scattering and Give Some Applications of it?

The transmitting process of light in all directions when it is incident on a particle which has a greater diameter is Scattering.

A few scattering applications are mentioned below.

2. The Sky Appears Blue. Give reason.

When white light passes via the atmosphere, violet, indigo, and blue colors encounter the suspended particles. These waves are then absorbed and scattered, and thus our eyes receive them.

3. The Sun Appears Yellow. Give reason.

Indigo, violet, and blue colors are scattered in the upper atmosphere. So, the resultant light is yellow. But, when this light enters our eyes, it appears as yellow.

4. The Sky Appears to be Dark, instead of Blue to an Astronaut. Give reason. 

There exist no particles in space; thus, there occurs no scattering. Hence, the sky appears to be dark.

5. Why do Stars Twinkle?

Stars emit light on their own, and they twinkle because of the atmospheric refraction of light. Stars are too far away from the earth. Thus, they are treated as point sources of light. When the light emitted from stars enters the earth's atmosphere, it gets refracted at different levels due to the variation in the air density at different levels of the atmosphere. Also, when the atmosphere refracts more star-light near to us, the star appears bright, and when the atmosphere refracts less star-light, then the star appears as dim. Thus, it appears as the stars are twinkling at night.

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