Human Eye and the Colorful World Class 10 – Continuing our series for Class 10 Revision for CBSE board exams, we bring you a new chapter today i.e. Human Eye and the colorful world Class 10. Generally, 2, 3 and 5 marks questions come from this chapter.
The concepts that are going to be discussed in this article are:
- Human Eye – Structure and Functioning
- Power of Accommodation
- Defects of vision and their correction
- Refraction of light through a prism
- Dispersion of light
- Formation of rainbow
- Atmospheric Refraction
- Scattering of Light
- Applications of scattering of light
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Let’s discuss each topic of Human Eye and the Colorful World Class 10 one-by-one
Human Eye – Structure and Functioning:
Let us first have a quick look at the structure of human eye. The diagram of human eye can be asked to draw in the exam, and functions of various parts can also be asked. Therefore, we suggest that you practice drawing it and study this topic thoroughly.
Here is the labelled diagram of human eye:
These are the functions of different parts of a human eye –
| Name of the part | Characteristic | Function |
| Cornea | Transparent spherical membrane covering the front part of the eye | Light enters the eye through this membrane; Most of the refraction happens here |
| Eye lens | transparent, biconvex structure in the eye | provides finer adjustment required to focus objects on the retina |
| Iris | Dark muscular diaphragm between the cornea and the lens | controls the size of the pupil |
| Pupil | An opening between the iris through which light enters the eye | regulates the amount of light entering the eye |
| Ciliary Muscle | Attached to the eye lens | hold the lens in position and modify the curvature of the lens. |
| Retina | light-sensitive surface of an eye on which the image is formed | generate signals which are transmitted to the brain through optical nerves |
| Optic nerve | Attached to retina | transmits visual information from the retina to the brain |
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Power of Accommodation:
The ability of the eye lens to adjust its focal length is called accommodation. This is done by changing the curvature of the eye lens.
The minimum distance at which objects can be seen most distinctly without strain is called near point of the eye. It is 25 cm for a normal human eye.
The farthest point up to which the eye can see objects clearly is called the far point of the eye. It is infinity for a normal eye.
Defects of vision and their correction
Now let us revise quickly various defects that can take place in human eye and their correction.
- Myopia: It is also known as nearsightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. It’s far point is nearer than infinity. Image is formed before retina in a myopic eye. It can be corrected by using a concave lens of suitable power. Here are the ray diagrams for a myopic eye and its correction –
- Hypermetropia: It is also known as far-sightedness. A person with this can see distant objects clearly but cannot see nearby objects distinctly. It’s near point more than 25 cm. Image is formed behind retina in this case.It can be corrected by using a convex lens of suitable power. Here are the ray diagrams for a hypermetropic eye and its correction –
- Some other defects and their correction measure are given on here:
-
Defect Symptoms Correction Presbyopia difficult to see Nearby as well as far away objects comfortably without
corrective eye-glasses
bi-focal lenses consisting of both concave and convex lenses
Cataract crystalline lens becomes milky and cloudy; partial or complete loss of vision Cataract Surgery
Refraction of light through a prism:
A triangular glass prism has two triangular bases and three rectangular lateral surfaces. These surfaces are inclined to each other. The angle between its two lateral faces is called the angle of the prism.
You can see the ray diagram of refraction taking place through a triangular glass prism.
Dispersion of Light:
The splitting of white light into band of seven colours through a prism is known as dispersion of light.
The various colours seen are Violet, Indigo, Blue, Green, Yellow, Orange and Red, as shown in the diagram.
Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism.
The red light bends the least while violet the most. Thus the rays of each colour emerge along different paths and thus become distinct.
Isaac Newton was the first to use a glass prism and also tried to split the colours of the spectrum of white light further by using another similar prism. However, he could not get any more colours.
He then placed a second identical prism in an inverted position with respect to the first prism, and obtained white light again. This implied that white light consists of seven colours.
Formation of Rainbow:
In the sky is also due to dispersion of sunlight by tiny water droplets, present in the atmosphere.They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop. A rainbow is always formed in a direction opposite to that of the Sun. You can see the ray diagram for rainbow formation.
Atmospheric Refraction:
The refraction of light taking place in the atmosphere is known as atmospheric refraction.
Atmospheric refraction is responsible for various phenomena, such as twinkling of stars, advanced sunrise and delayed sunset etc. These phenomena are very important and you can study them in detail with this video below:
Scattering of Light:
Another important phenomena related to light is scattering of light. The reflection of light from an object in all directions is called scattering of light. The scattering of light depends on the size of the scattering particles and wavelength of the light.
The phenomenon in which light is scattered by very small particles in its path that makes the particles visible is known as Tyndall effect or Tyndall scattering.This phenomenon is seen when a fine beam of sunlight enters a smoke-filled room through a small hole or when sunlight passes through a canopy of a dense forest, where tiny water droplets in the mist scatter light.
Applications of Scattering of Light:
There are many phenomena taking place around us because of scattering of light, let’s study them one by one.
- Colour of sun at sunrise and sunset: The reddish appearance of the sun at sunrise or sunset is due to scattering of light.
- Light from the sun near the horizon passes through thicker layers of air and covers the larger distance in the earth’s atmosphere before reaching our eyes
- Most of the blue light and light of shorter wavelength is scattered away by the particles.
- So, only red light, being of higher wavelength reaches us which gives reddish appearance of the sun at sunrise or sunset.
You can see its diagrammatic representation below:
- Why is the color of sky blue? : During the daytime, the sky appears blue. This is because the size of the particles in the atmosphere is smaller than the wavelength of visible light, so they are more effective in scattering the light of shorter wavelengths i.e. blue light.