the human eye colourful warld
Answers
Answer:
It's funny because in this lesson we are going to learn about defects of vision and their correction ,scattering,dispersion of light if u have any doubt on scattering or dispersion ask me ok friends bye
Explanation:
Human Eye: working of human eye, Persistence of vision, Power of accommodation of human eye, Defects of vision.
The Human Eye: It is a natural optical instrument which is used to see the objects by human beings. It is like a camera which has a lens and screen system.
Structure of the Human Eye
Human Eye and Colourful World Class 10 Notes Science Chapter 11 1
The various parts of eye and their functions :
Retina: It is a light sensitive screen inside the eye on which image is formed. It contains rods and cones.
Cornea: It is a thin membrane which covers the eye trail. It acts like a lens which refracts the light entering the eye.
Aqueous humour: It is fluid which fills the space between cornea and eye lens.
Eye lens: It is a convex lens made of transparent and flexible jelly like material. Its curvature can be adjusted with the help of ciliary muscles.
Pupil: It is a hole in the middle of iris through which light enters the eye. It appears black because light falling on it goes into the eye and does not come back.
Ciliary muscles: These are the muscles which are attached to eye lens and can modify the shape of eye lens which leads to the variation in focal lengths.
Iris: It controls the amount of light entering the eye by changing the size of the pupil.
Optical nerve: These are the nerves which take the image to the brain in the form of electrical signals.
The human eye is roughly spherical in shape with a diameter of about 2.3 cm. It consists of a convex lens made up of living tissues. Hence, human lenses are living organs contrary to the simple optical lenses. The following table lists the main parts of the human eye and their respective functions.
S.No. Human Eye Part Functions
1. Pupil Opens and closes in order to regulate and control the amount of light.
2. Iris Controls light level similar to the aperture of a camera.
3. Sclera Protects the outer coat.
4. Cornea A thin membrane which provides 67% of the eye’s focusing power.
5. Crystalline lens Helps to focus light into the retina.
6. Conjunctive Covers the outer surface (visible part) of the eye.
7. Aqueous humour Provides power to the cornea.
8. Vitreous humour Provides the eye with its form and shape.
9. Retina Captures the light rays focussed by the lens and sends impulses to the brain via the optic nerve.
10. Optic nerve Transmits electrical signals to the brain.
11. Ciliary muscles Contracts and extends in order to change the lens shape for focusing.
How Pupil Works?
For Example, You would have observed that when you come out of the cinema hall after watching the movie in the bright sunlight, your eyes get closed. And when you entered the hall from the bright light, you won’t be able to see and after some time you would be able to see. Here, the pupil of an eye provides a variable aperture, whose size is controlled by iris.
(a) When the light is bright: Iris contracts the pupil, so that less light enters the eye.
(b) When the light is dim: Iris expands the pupil, so that more light enters the eye.
Pupil opens completely when iris is relaxed.
Persistence of Vision: It is the time for which the sensation of an object continue in the eye. It is about 1/16th of a second.
Power of Accommodation: The ability of the eye lens to adjust its focal length accordingly as the distances is called power of accommodation.
Human Eye and Colourful World Class 10 Notes Science Chapter 11 2
Colour Blindness: A person having defective cone cells is not able to distinguish between the different colours. This defect is known as Colour Blindness.
Defects of Vision and their Correction
Myopia (Short-sightedness): It is a kind of defect in the human eye due to which a person can see near objects clearly but he cannot see the distant objects clearly. Myopia is due to
(i) excessive curvature of the cornea.
(ii) elongation of eyeball.
Human Eye and Colourful World Class 10 Notes Science Chapter 11 3
Correction: Since a concave lens has an ability to diverge incoming rays, it is used to correct this defect of vision. The image is allowed to format the retina by using a concave lens of suitable power as shown in the given figure.
Human Eye and Colourful World Class 10 Notes Science Chapter 11 4
Hypermetropia (Long-sightedness): It is a kind of defect in the human eye due to which, a person can see distant objects properly but cannot see the nearby objects clearly. It happens due to
(i) decrease in the power of eye lens i.e., increase in focal length of eye lens.
(ii) shortening of eyeball.
Human Eye and Colourful World Class 10 Notes Science Chapter 11 5
A hypermetropic eye has its least distance of distinct vision greater than 25 cm.
Correction: Since a convex lens has the ability to converge incoming rays, it can be used to correct this defect of vision, as you already have seen in the animation. The ray diagram for the corrective measure for a hypermetropic eye is shown in the
.