Short and Concise Human Eye and the Colorful World Notes
In the previous chapter, you studied light and some of its properties like the refraction of light. You also studied the image formation by spherical lenses.
We will use these concepts to study the human eye, the work of the lens in the human eye, the different types of defects, and the ways to correct the defects.
You will also study the different optical phenomena in nature. You will study the rainbow formation, the twinkling of stars, the scattering of light, the blue appearance of the sky, and the red appearance of the sun during sunset and sunrise.
Note: The content uploaded here will be complete as per the topics discussed in the CBSE NCERT book.
Topics to be discussed-
- About the Human Eye and How it Works
- Power of Accommodation of Eye
- Defects of Vision- Myopia, Hypermetropia, Presbyopia, Astigmatism
- Correction of defects of vision
- Refraction of Light through prism
- Dispersion of White Light by a glass prism
- Rainbow formation
- Atmospheric Refraction and some optical phenomena in nature
- Scattering of Light
- Tyndall Effect
- Red appearance of the Sun at sunrise and sunset and White appearance at noon
The human is a remarkable organ that is responsible for our sense of vision. It helps us to see the beautiful and colorful world around us. The human eye is roughly spherical in shape and consists of several parts.
Structure of the Human Eye
The human eye can be divided into three layers- Sclera, Choroid, and Retina.
Sclera- It is the outermost layer of the eye that tough and protects the eyeball.
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Question: Define the Far Point, Near Point, and Least Distance of distinct vision.
Far Point: The far point of an eye can be defined as the farthest point up to which the eye can see clearly. The far point of a normal eye is infinity.
Near Point: The near point is the nearest distance up to which the eye can see clearly. The near point of a normal eye is about 25 cm from the eye.
Least Distance: The minimum distance up to which the eye can see an object clearly without any strain on the eye. It is equal to the distance between the eye and the near point.
Note: The least distance of a person increases with age.
Accommodation of the Eye
It is also called the Power of Accommodation of the Eye.
- The Power of Accommodation of the Eye is its ability to change the shape of the lens to focus on objects that are close or far away.
- When you look at something up close, the lens becomes thicker to focus the image on the retina.
- When you look at something far away, the lens becomes thinner.
This adjustment allows you to see objects clearly at different distances.
Defects of Vision
What is defects of vision?
Defects of vision can be defined as abnormalities in the eye that affect a person’s ability to see clearly. These defects can result in blurry vision, difficulty focusing, or other issues in perceiving the visual world.
- Defects of vision, also known as visual impairments or vision problems.
Some common Defects of Vision
Here is a list of some common defects of vision that are discussed in your NCERT book.
1. Myopia or Nearsightedness
In this type of eye defect, a person can see near objects clearly but cannot see far or distant objects clearly. The distant objects are seen as blurry.
Causes of Myopia
Myopia is mainly caused due to the following two reasons-
- Elongation of the eyeball (increase in the length of the eyeball)
- eye lens becomes more convergent or focal length decreases
Correction of Myopia
The person having a myopic eye can get rid of this by using spectacles made up concave lens of suitable focal length. The concave lens which is diverging in nature will help compensate for the increased converging power of the eye lens.
2. Hyperopia or Hypermetropia or Farsightedness
In this type of defect, a person can see distant objects clearly but the nearby objects appear blurry.
Causes of Myopia
- Shortening of the eyeball (decrease in the length of the eyeball)
- eye lens becomes less convergent or the focal length increases
Correction of Myopia
Convex lens of suitable power or focal length.
This age-related condition affects near vision as the lens loses its flexibility over time. This defect is also called old age longsightedness.
Causes of Presbyopia
- Loss of Lens Flexibility
- Weakening of Ciliary Muscles
- Changes in Lens Protein
Correction of Presbyopia
Presbyopia can be corrected with the help of a convex lens of suitable power.
Refraction of Light through a Prism
We have already studied the refraction of light through a glass slab. Now let us study the refraction of light through a Prism.
What is a Prism?
It is a transparent material, usually bounded by two triangular plane surfaces (called bases), and three rectangular surfaces.
The surfaces of the prism are inclined to each other at some angle (usually 45° and 60°).
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