Notes of Human Eye and Colourful World Class 10

Welcome to our article on "Notes of Human Eye and Colourful World Class 10". In this article, we will explore the fascinating world of color and vision, focusing on the human eye and how it perceives the world around us. We will delve into the structure of the eye, the different types of cells involved in vision, and the complex neural processes that allow us to see colors and perceive depth. By the end of this article, you will have a deeper understanding of how our eyes work and how we perceive the colorful world around us. So, let's get started!

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Human Eye: working of human eye, Persistence of vision, Power of accommodation of human eye, Defects of vision.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 -Notes of Human Eye and Colourful World Class 10

The various parts of eye and their functions :

How Pupil Works?

You may have observed that when you exit a cinema hall after watching a movie in bright sunlight, your eyes tend to close. Conversely, when you enter the hall from bright light, you initially experience difficulty seeing but eventually adjust. This is because the pupil of the eye provides a variable aperture, the size of which is controlled by the iris.

• In bright light, the iris contracts the pupil to allow less light into the eye.
• In dim light, the iris expands the pupil to allow more light into the eye.
• The pupil opens completely when the 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.

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Power of Accommodation: The ability of the eye lens to adjust its focal length accordingly as the distances is called power of accommodation.

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-Notes of Human Eye and Colourful World Class 10

Myopia (Short-sightedness): Myopia is a type of defect in the human eye that causes a person to see nearby objects clearly, but distant objects appear blurry. Myopia is caused by:

• Excessive curvature of the cornea
• Elongation of the eyeball

Correction: To correct this vision defect, a concave lens is utilized because it has the ability to diverge incoming rays. By using a concave lens of appropriate power, the image can be formed on the retina, as shown in the figure below.

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Hypermetropia (Long-sightedness): Hypermetropia is a type of vision defect that causes a person to see distant objects clearly, but nearby objects appear blurry. This defect is caused by:

• Decrease in the power of the eye lens, resulting in an increase in the focal length of the eye lens.
• Shortening of the eyeball.

A hypermetropic eye has its least distance of distinct vision greater than 25 cm.

Correction: To correct this vision defect, a convex lens is utilized because it has the ability to converge incoming rays, as demonstrated in the animation. The ray diagram for correcting a hypermetropic eye is shown in the figure below.

Power of the correcting convex lens: -Notes of Human Eye and Colourful World Class 10

To calculate the focal length and power of the lens required to correct myopia, the Lens formula, 1v−1u=1f can be used. In this scenario, the object distance, u is infinite and the image distance, v is the person's far point. The focal length, f needs to be determined.

On solving the lens formula, we get:

1v−1u=1f

1v=1f

v=f

Therefore, the focal length of the lens required to correct myopia is equal to the person's far point.

For a concave lens, the image is formed in front of the lens, on the same side as the object. The focal length can be calculated as the negative of the far point.

The power of the required lens (P) can be calculated using the formula:

P = 1/f (in meters)

Power of the correcting convex lens: -Notes of Human Eye and Colourful World Class 10

The lens formula, 1v-1u=1f, enables us to determine the focal length f and therefore, the power P of the convex lens used to correct the defect, with the following parameters:

• Object distance, u = -25 cm, the normal near point
• Image distance, v = defective near point Therefore, the lens formula can be simplified to 1v+125=1f.

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Presbyopia: Age-related presbyopia is a type of defect in the human eye that occurs due to ageing, and it is caused by the following factors: (i) A decrease in the flexibility of the eye lens. (ii) Gradual weakening of ciliary muscles. As a result, a person may experience both myopia and hypermetropia.

Correction: To correct presbyopia, people use bifocal lenses with appropriate power. Bifocal lenses contain both concave and convex lenses, where the upper portion has a concave lens and the lower portion has a convex lens.

Astigmatism: It is a kind of defect in human eye due to which a person cannot see (focus) simultaneously horizontal and vertical lines both.

Correction: By using a cylindrical lens.

Cataract:

• The growth of a membrane over the eye lens causes it to become hazy or opaque, resulting in decreased or lost vision. This condition is known as cataract, which can only be corrected through surgery.
• When light passes through a prism, it undergoes refraction and is split into its component colors due to the varying angles of deviation. This phenomenon is known as dispersion of light.
• White light is composed of a combination of colors with different wavelengths. These colors include red, orange, yellow, green, blue, indigo, and violet, arranged in increasing order of their wavelengths.
• The process of combining these individual colors to form white light is called recombination. This occurs when the different colors of the spectrum are mixed in appropriate proportions.
• The recombination of the spectrum colors can result in the formation of a rainbow, which is a natural phenomenon that occurs due to the reflection, refraction, and dispersion of sunlight by water droplets in the atmosphere.

Refraction of light through a prism: When a ray of light is incident on a rectangular glass slab, after refracting through the slab, it gets displaced laterally. As a result, the emergent ray comes out parallel to the incident ray.

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Unlike a rectangular slab, the side of a glass prism are inclined at an angle called the angle of prism.

Prism: A prism has two triangular bases and three

Angle of Prism: Angle between two lateral faces is

Angle of Deviation: The angle between the incident deviation.

Dispersion of white light by a glass prism - Notes of Human Eye and Colourful World Class 10

• When white light passes through a glass prism, it splits into its seven constituent colors, a phenomenon known as dispersion of white light.
• The seven colors seen in the spectrum are Violet, Indigo, Blue, Green, Yellow, Orange, and Red, which can be remembered by the acronym VIBGYOR.
• Each color of light bends at a different angle with respect to the incident angle, causing the colors to spread out.
• The violet light bends the least, while the red light bends the most.
• The band of seven colors that make up the spectrum is called the spectrum itself.

Composition of white light: White light consists of seven colours i.e., violet, indigo, blue, green, yellow, orange and red.

Monochromatic light: Light consisting of single colour or wavelength is called monochromatic light, example; sodium light.

Polychromatic light: Light consisting of more than two colours or wavelengths is called polychromatic light, example; white light.

Recombination of white light: Newton found that when an inverted prism is placed in the path of dispersed light then after passing through the prism, they recombine to form white light.

Issac Newton: 

1. The credit of obtaining the spectrum of sunlight using a glass prism goes to him.
2. He attempted to split the spectrum of white light further by using a second similar prism, but failed to get any additional colors.
3. He repeated the experiment using a second prism in an inverted position with respect to the first prism.
4. This allowed all the colors of the spectrum to pass through the second prism, and he observed white light emerging on the other side of the second prism.
5. Based on his observations, he concluded that the sun is made up of the seven visible colors of VIBGYOR.

Rainbow: It is the spectrum of sunlight in nature. It is formed due to the dispersion of sunlight by the tiny water droplet, present in the atmosphere.

Formation of the rainbow

1. Water droplets refract and disperse incident sunlight, reflect it internally, and refract it again upon exiting, acting like small prisms.
2. This dispersion and internal reflection cause different colors to reach the observer's eye, with red appearing on top and violet at the bottom of the rainbow.
3. A rainbow is formed in a direction opposite to that of the Sun.
4. At point A, refraction and dispersion occur.
5. At point B, internal reflection takes place.
6. At point C, refraction and dispersion occur.

Atmospheric Refraction: The refraction of light caused by the Earth’s atmosphere (having air layers of varying optical densities) is called Atmospheric Refraction.

Appearance of Star Position - Notes of Human Eye and Colourful World Class 10

Twinkling of Star

• Atmospheric refraction causes the twinkling effect of stars.
• Distant stars act as a point source of light, and the beam of starlight deviates from its path due to the changing refractive index of the Earth's atmosphere, bending towards the normal and causing the apparent position of the star to change.
• Planets do not twinkle because they are closer to Earth and are seen as an extended source of light, which nullifies the twinkling effect caused by individual point sources of light.
• If there were no atmosphere on Earth, the duration of daylight would be approximately 4 minutes shorter because actual sunrise and sunset happen when the sun is below the horizon, and the rays of light from the sun reach our eyes due to atmospheric refraction.
• The apparent flattening of the Sun's disc at sunset and sunrise is due to atmospheric refraction.
• Scattering of light follows Rayleigh's Law, which states that the amount of scattered light is inversely proportional to the fourth power of the wavelength (λ). As the wavelength increases, the scattering of light decreases.

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Tyndall Effect

1. When a beam of light strikes the minute particles of Earth's atmosphere, suspended dust particles, and air molecules, the path of the beam becomes visible.
2. Tyndall Effect is the phenomenon of light scattering by colloidal particles.
3. Tyndall Effect can be observed when sunlight passes through a dense forest canopy.
4. The color of the scattered light depends on the size of the scattering particles.

Colour of Sunrise and Sunset -Notes of Human Eye and Colourful World Class 10

• During sunset and sunrise, the sun and its surroundings appear red.

• The sunlight has to travel a larger distance in the atmosphere due to the sun's position near the horizon.

• The shorter wavelength blue light gets scattered away by particles in the atmosphere, while the longer wavelength red light reaches our eyes.

• This is why the sun appears red in color during sunset and sunrise.

• Red is used as the color for danger signals or signs.

• Red light has the maximum wavelength in the visible spectrum, making it scatter the most when it strikes small particles of fog and smoke.

• Therefore, red can be seen clearly from a larger distance.

• At noon, the sun appears white.

• The sun is directly overhead, and sunlight travels a shorter distance through the atmosphere at this time.

• Only a little of the blue and violet colors get scattered, resulting in the sun appearing white.

Human Eye: It is a wonderful gift of nature to the human body. Human eye is nearly spherical in shape of diameter about 2.5 cm.

Parts of Human Eye

• Cornea: It is the protective and front layer of the eye. It is made by a transparent membrane. Light enters the eye through the cornea.
• Iris: Dark and a colourful muscular diaphragm is called iris. It is responsible for colour of the eye.
• Pupil: Small circular hole in the centre of iris. It regulates the amount of light entering the eye by adjusting the size of the iris.
• Ciliary Muscles: It holds the eye lens at its proper position. It changes the size of eye lens.
• Eye lens: The eye lens is a convex lens made by the transparent jelly like material.
• Retina: It is the screen of the eye. A real and inverted image form on the retina.
• Rods and Cones: These are colour sensitive rods and cones shaped cells. Rods are responsible for the vision in dim light while cones are responsible for colour.
• Optic Nerve: It converts information of the image into a corresponding electric signal and passes it to the brain.
• Blind Spot: The junction of the optic nerve and retina, where no rods and cones cells are present is called the blind spot. It is insensitive to light.

Near Point: The nearest point from eye at which the eye can see clearly without strain is called near point. For normal eye it is 25 cm.

Far Point: The farthest point, upto which the eye can see the object clearly is called far point. For normal eye it is infinity.

The range of Vision: Distance between near point and far point of eye is called range of vision.

Power of Accommodation: The ability of the eye to see near as well as far objects clearly is called Power of Accommodation.

Myopia (Nearsightedness): 

The eye is unable to see far-off objects clearly but can see near objects clearly in this defect.

Reasons for this defect are:

1. The size of the eyeball increases.
2. The cornea becomes excessively curved.
3. The power of the eye lens increases (or focal length decreases).

Correction: It is corrected by using concave lens of suitable focal length.

Hypermetropia (Far sightedness): In this defect eye is unable to see nearby objects clearly but is able to see far objects clearly.
Reason.

• Due to decrease in size of eye ball
• Due to decrease in power (or increase in focal length) of eye lens.

Correction: It is corrected by using a convex lens of suitable focal length.

Dispersion of Light: Splitting of white light into seven colours is called dispersion. Example, the formation of Rainbow (VIBGYOR). Violet deviates the most but red deviates least.

1. The human eye is one of the most valuable and sensitive sense organs. It enables us to see the wonderful world and the colours around us.

2. The eyeball is approximately spherical in shape with a diameter of about 2.3 cm.

3. Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea. The crystalline lens merely provides the finer adjustment of focal length required to focus.

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4. The human eye has the following parts :

• Cornea : The transparent spherical membrane covering the front of the eye.
• Iris: The coloured diaphragm between the cornea  and lens.
• Pupil: The small hole in the iris.
• Eye lens : It is a transparent lens made of jelly like material.
• Ciliary muscles: These muscles hold the lens in position.
• Retina: The back surface of the eye.
• Blind spot: The point at which the optic nerve leaves the eye. An image formed at this point is not sent to the brain.
• Aqueous humour: A clear liquid region between the cornea and the lens.
• Vitreous humour: The space between eye lens and retina is filled with another liquid called vitreous humour.

5. The eye is unable to see far-off objects clearly but can see near objects clearly in this defect.

Reasons for this defect are:

1. The size of the eyeball increases.
2. The cornea becomes excessively curved.
3. The power of the eye lens increases (or focal length decreases).

6. Accommodation 

• The ciliary muscles play a vital role in the accommodation of the eye.
• Accommodation refers to the ability of the eye to adjust its focal length in order to focus on both near and distant objects.
• The process of changing the focal length of the eye lens is called accommodation.
• Accommodation is necessary for a clear and sharp vision.

7. Defects of the Eye : Although the eye is one of the most remarkable organs in the body, it may have several abnormalities, which can often be corrected with eyeglasses, contact lenses, or surgery. The various defects from which an eye can suffer are (i) Hypermetropia or long sightedness, (ii) Myopia or shortsightedness and (iii) Astigmatism, (iv) Presbyopia.

8. Hypermetropia, hyperopia, or long sightedness : A person suffering from this defect can see distant objects I clearly but cannot see nearby objects clearly. In this defect, the near point lies farther away than 25 cm. Hypermetropia (far sightedness — the image of nearby objects is focussed beyond the retina) is corrected by using a convex lens of suitable power. The eye loses
its power of accommodation at old age.

9. Hypermetropia is due to the following reasons :

• Either the hyperopic eyeball is too short or
• The ciliary muscle is unable to change the shape
  of the lens enough to properly focus the image i.e. the focal length of the eye lens increases.

10. Myopia or short sightedness or near sightedness: A person suffering frommyopia or short sightedness can see nearby objects clearly but cannot see the far away objects clearly. Myopia (short sightedness — the image of distant objects is focussed before the retina) is corrected by using a concave lens of suitable power.

11. This defect is due to the following reasons :

• Either the eyeball is longer than normal or
• The maximum focal length (due to excessive curvature of the cornea) of the lens is insufficient to produce a clearly formed image on the retina.

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12. Astigmatism is a condition in which the retina produces a line image instead of a point image when light from a point source enters the eye, causing a person to have unequal visual abilities in different directions. This occurs when the cornea or crystalline lens is not perfectly spherical, but can be corrected with cylindrical lenses having different curvatures in two mutually perpendicular directions.

13. Bifocal lenses are used to correct the vision of a person who suffers from both myopia and hypermetropia. The upper half of the lens is concave for distant vision, while the lower half is convex for reading.

14. Presbyopia, or "old sight," is a condition in which an older person cannot read or write comfortably due to a decrease in the eye's ability to focus on near objects. This can be corrected by using spectacles with a convex lens of suitable focal length.

15. Hypermetropia occurs when the eye lens' focal length increases or the eyeball length decreases, while presbyopia is caused only by an increase in the eye lens' focal length. Cataract surgery, which involves removing the eye lens and replacing it with a lens of suitable focal length, can correct the problem of decreased vision.

16.Having two eyes provides humans with a wider horizontal field of view, allowing us to see in three  dimensions with depth perception. Each eye observes a slightly different image, and the brain combines the two views into one, giving us the ability to perceive distances.

17. Donating one's eyes after death can provide vision to two corneal blind individuals. Eye donors of any sex or age group, including those with non-communicable diseases such as diabetes, hypertension, and asthma, as well as those who wear spectacles or have undergone cataract surgery, can donate their eyes.

18. The near point of the eye, or the minimum distance at which a person can see objects clearly without strain, is approximately 25 cm for a young adult with normal vision.

19. The image of an object persists on the retina for 1/16 second after it is removed. The projection of still pictures taken by a movie camera at a rate of approximately 24 images per second creates the illusion of moving images.

20.The retina of the eye contains two types of light-sensitive cells: rod-shaped cells that respond to the brightness or intensity of light and cone-shaped cells that respond to color, enabling humans to distinguish between different colors.

21. Color blindness is a genetic disorder that causes a person to be unable to distinguish between different colors, even though their vision is otherwise normal. There is currently no cure for this condition.

22. The farthest point at which a short-sighted eye can see clearly is known as the far point of the eye, while the nearest point at which a long-sighted eye can see clearly is known as the near point of the eye. For a normal eye, the far point is infinity, and the near point is approximately 25 cm from the eye.

25. Farpoint: The farthest point upto which a short sighted eye can see clearly is called the far point of the eye. For a normal eye, the far point is infinity.

26. Near point : The nearest point upto which a long sighted eye can see clearly is called the near point of the eye. For a normal human eye, of an adult, the near point is about 25 cm from the eye.

27. Least cfistance of distinct vision: The minimum distance upto which an eye can see clearly is called the legist distance of distinct vision ; it is normally denoted by D. The least distance of distinct vision is equal to the distance between the eye and its near point. For a normal human eye, this distance is around 25 cm.

28. The distance between far point and near point of the eye is called range of vision of the eye.

29. When white light passes through a prism, the violet light bends most and the red light bends the least. Dispersion of light is the phenomenon of splitting of white light into its constituent seven colours on passing through a glass prism. The band of seven colours so obtained is called visible spectrum.

30. The seven colours of white light are violet, indigo, blue, green, yellow, orange and red. It is remembered by the acronym VIBGYOR.

31. Isaac Newton was the first to use a prism to obtain a spectrum of sunlight.

32. Spectrum is the band of distinct colours we obtain when white light is split by a prism.

33. Cause of dispersion : Every colour has its own characteristic wavelength/frequency. Different colours move with same speed in air/vacuum. But their speeds in refracting media like glass are different. Therefore, refractive index of the medium for different colours is different. As a result, different colours undergo different deviations on passing through the prism. Hence, different colours emerge from the prism along different directions.

34. The speed of light in vacuum is same for all wavelengths, but the speed in a material substance is different for different wavelengths.

35. In any medium other than air/vacuum red light travels the fastest and violet light travels the slowest.

36. The most familiar form of electromagnetic radiation may be defined as that part of the spectrum that the human eye can detect. Light is produced by the rearrangement of electrons in atoms and molecules. The various wavelengths of visible light are classified with colours ranging from violet (λ = 4 x 10^-7 m) to red (λ = 7 x 10^-7 m). The eye’s sensitivity is a function of wavelength, the sensitivity being a maximum at a wavelength of about λ = 5.6 x 10^-7 m (yellow-green).

37. When we pass white light through two ideptical prisms held side by side with their refracting edges in opposite directions; the first prism disperses white light into seven colours and the second prism recombines the seven colours into white light. Thus, light emerging from 2nd prism is white.

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38. A rainbow is formed due to dispersion of light by tiny droplets of water which act as prisms.

39. Atmospheric refraction is the cause of twinkling of stars, advance sunrise and delayed sunset.

40. Scattering of light causes the blue colour of sky and the reddening of the Sun at sunrise and sunset

Notes of Human Eye and Colourful World Class 10

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