Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes
Topics Covered: (Human Eye and Colourful world Class 10)
- Overview of the Human Eye
- Components of the Human Eye
- Near Point or the Minimum Distance for Clear Vision
- Myopia (Near-sightedness)
- Causes & Corrective Measures of Myopia
- for Myopia
- Hypermetropia (Far-sightedness)
- Causes & Corrective Measures of Hypermetropia
- Presbyopia (Age-related Hypermetropia)
- Causes & Corrective Measures of Presbyopia
- Advantages of Forward-facing Eyes
- Light Refraction through a Prism
- Total Internal Reflection
- Scattering Phenomenon
- Tyndall Effect
- Dependence of Light Scattering on Color
- Why are Emergency Signs Red?
- Why the Sky Appears Blue on Clear Days
- Why Astronauts See the Sky Differently in Space
- Why Clouds Appear White
- Why the Sun Appears Red During Sunrise and Sunset
Overview: Human Eye and Colourful world Class 10
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| Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
- The Human Eye is the sensory organ that enables vision, and it is located within the eye sockets in the skull.
- The average diameter of the eyeball is about 2.3 cm.
Components of the Human Eye: (Human eye and colourful world class 10)
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| Components of the Human Eye:Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
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Cornea: The outermost layer of the eye that is transparent. It is responsible for most of the light refraction entering the eye.
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Lens: Made of a jelly-like fibrous material, the lens focuses the light to form a real and inverted image on the retina. It is a convex lens that converges light to focus on the retina.
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Iris: A dark, muscular structure that regulates the size of the pupil to control the amount of light entering the eye.
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Pupil: The central opening of the iris, which adjusts in size to control how much light can enter the eye.
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Retina: A thin, sensitive layer of tissue at the back of the eye, filled with cells that respond to light.
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Far Point: The farthest distance at which the eye can see an object clearly. For a healthy adult, this is at infinity.
Near Point or Minimum Distance of Clear Vision:
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The closest distance at which the eye can clearly distinguish an object without strain.
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The typical near point for a normal human eye is 25 cm.
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Accommodation: The ability of the lens to adjust its focal length to focus on objects at varying distances. This is controlled by the ciliary muscles.
- The focal length increases when the ciliary muscles relax, making the lens thinner.
- The focal length decreases when the ciliary muscles contract, making the lens thicker.
Myopia (Near-sightedness)
- A person with myopia can clearly see objects that are close, but has difficulty seeing objects that are far away.
- The image is formed in front of the retina, rather than on it.
Causes of Myopia
- The eye's lens may be excessively curved.
- The eyeball may be too elongated.
Correction of Myopia
- Myopia is corrected by using a concave lens with the appropriate power.
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| Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
(i) In myopia, the image of distant objects is focused in front of the retina instead of directly on it.
(ii) The farthest point (F) that a person with myopia can clearly see is closer than infinity.
(iii) To correct myopia, a concave lens is used in front of the eye. This lens creates a virtual image of distant objects at the far point (F) of the myopic eye.
Hypermetropia (Far-sightedness)
- A person with hypermetropia can see distant objects clearly but has difficulty focusing on nearby objects.
- The near point of the eye is farther than normal.
- The image is formed behind the retina.
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| Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
Causes of Hypermetropia
- The focal length of the eye's lens becomes too long.
- The eyeball is smaller than usual.
Correction of Hypermetropia
- The condition can be corrected by using a convex lens with the appropriate power.
Presbyopia (Age-related Hypermetropia)
- Presbyopia is a vision impairment commonly found in older individuals, where they struggle to see objects up close due to a decrease in the eye's accommodation ability.
- The near point of someone with presbyopia gradually moves further away, exceeding the normal 25 cm distance.
Causes of Presbyopia
- Weakening of the ciliary muscles over time.
- Reduced flexibility of the eye lens.
Correction of Presbyopia
- The condition can be corrected with a convex lens of the appropriate strength.
- In some cases, individuals may experience both myopia and hypermetropia, requiring bifocal lenses for correction.
Advantage of Forward-facing Eyes
- It provides a broader field of vision.
- It improves the ability to detect faint or distant objects.
- It allows for depth perception, providing a three-dimensional view.
Refraction through a Glass Prism
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| Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
Prism: A piece of transparent glass shaped like a pyramid, with two triangular bases and three rectangular side surfaces.
Angle of Prism (A): The angle formed between two adjacent side surfaces of the prism.
- Angle of Deviation (D): It is the angle formed between the incoming ray and the outgoing ray after passing through the prism.
When white light passes through a glass prism, it breaks into its seven component colors, creating a band of colors. This process is known as dispersion.
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| Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
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Spectrum: The band of seven colors produced by the dispersion of white light is called the spectrum.
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Acronym: A sequence of letters representing the colors of the spectrum: V I B G Y O R.
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Angle of Deviation is inversely proportional to the wavelength.
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Red has the longest wavelength, and therefore, it is the least deviated color.
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Violet, with the shortest wavelength, is the most deviated color in the visible spectrum.
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Isaac Newton was the first to demonstrate that sunlight consists of seven colors:
(i) He passed sunlight through a glass prism, creating a band of seven distinct colors.
(ii) He attempted to further split these colors by placing another prism in front of the first one, but he was unable to produce additional colors.
(iii) Newton then used a second, identical prism but inverted. When the seven colors passed through it, they combined to form white light again.
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| Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
Total Internal Reflection
- Total internal reflection occurs when light travels from a denser medium to a rarer medium at an oblique angle, and the angle of incidence surpasses the critical angle. In this case, the light is reflected back into the denser medium instead of refracting.
Conditions for Total Internal Reflection:
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Light must enter the rarer medium obliquely from a denser medium.
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The angle of incidence must be greater than the critical angle for total internal reflection to occur.
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Critical Angle: It is the angle of incidence at which the angle of refraction becomes 90º, meaning the refracted ray travels along the boundary between the two mediums.
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Rainbow: A natural spectrum of light that appears in the sky after rain. A rainbow is seen in the direction opposite to the sun.
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| Total Internal Reflection : Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
Phenomena Involved in Rainbow Formation:
Three key phenomena that contribute to the formation of a rainbow are:
- Dispersion
- Refraction
- Internal Reflection
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After rainfall, some water droplets remain suspended in the air. These droplets act like small prisms.
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When light enters these water droplets, it first undergoes refraction and dispersion, separating into its component colors.
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The light then reflects internally off the back of the droplet and exits, undergoing another refraction. As a result, the seven colors appear as a rainbow to the observer.
Atmospheric Refraction:
Atmospheric refraction refers to the bending of light as it passes through different layers of the atmosphere.
Common effects caused by atmospheric refraction include:
- The apparent flickering of objects seen behind a hot surface or fire.
- Stars near the horizon appear slightly higher than their actual position.
- Early sunrise and delayed sunset.
- The apparent flattening of the Sun’s disk.
- The twinkling of stars.
Apparent Flickering of Objects Behind a Hot Object:
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When an object is observed behind a hot surface, such as fire, it may appear to flicker.
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The air above the hot surface becomes warmer and rises, and cooler air fills the space. Since the refractive index of hot air is lower than that of cooler air, the air’s physical properties are not uniform.
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As the refractive index of the medium changes, light appears to come from different directions. This causes the object to appear as though it is fluctuating or flickering in position.
Stars near the horizon appear slightly higher than their actual position.
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| Stars near the horizon appear slightly higher than their actual position. Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
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The refractive index of Earth's atmosphere generally increases with altitude, from top to bottom.
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When light from a star near the horizon travels through the atmosphere, it moves from a less dense to a denser medium, causing it to bend toward the normal.
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As a result, the star seems to be positioned higher in the sky than it actually is.
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| Early sunrise and delayed sunset. Human Eye and Colourful World | Class 10 Human eye and colourful world notes | Class 10 Science chapter 11 | human eye class 10 notes |
The sun appears about two minutes earlier than the actual sunrise and remains visible for roughly two minutes after the real sunset.
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When the sun is below the horizon, its rays travel from a rarer to a denser medium, causing them to bend towards the normal.
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As a result, the sun seems to be higher in the sky than its true position.
Twinkling of Stars
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Stars are extremely distant, making them appear as point sources of light.
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Since the Earth's atmospheric conditions are constantly changing, the light from stars appears to come from different directions.
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This causes the apparent position of the star to fluctuate.
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The intensity of light from stars also changes because of variations in the refractive index of the atmosphere.
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When more light from a star reaches our eyes, it appears brighter, and when less light reaches us, the star appears dimmer.
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These fluctuations in brightness and position result in the twinkling of stars.
Scattering Effect
Scattering refers to the spreading of light in various directions by particles in a medium.
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Scattering ∝ 1/wavelength
- Tyndall Effect: This occurs when light passes through a colloidal medium, making the path of light visible. This phenomenon is known as the Tyndall effect.
Examples include:
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When light enters a dark, dusty room through a slit or ventilator, the path of light becomes visible.
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The path of light can also be seen when it passes through the dense canopy of trees in a forest.
Dependence of Color of Scattered Light:
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Fine particles: These scatter mainly the blue light (which has a shorter wavelength).
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Medium-sized particles: These scatter mainly the red light (which has a longer wavelength).
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Larger particles: These scatter all the colors of light, which is why they appear white.
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The wavelength of red light is about 1.8 times longer than that of blue light.
Red Color for Danger Signs:
- Red is the least scattered color, meaning it can travel longer distances through fog and smoke without losing its intensity. This is why red is used for warning and danger signs.
Blue Color of the Sky on Clear Days:
- The upper layers of the atmosphere contain fine particles of water vapor and gases. These particles are more effective at scattering shorter wavelengths of light, primarily blue, than longer wavelengths. This is why the sky appears blue.
Appearance of the Sky to an Astronaut in Space:
- To an astronaut in space, the sky appears dark because there are fewer particles at such high altitudes, and thus scattering is minimal.
Clouds Appearing White:
- Clouds are made of water droplets formed from condensed water vapor. Due to the larger size of the droplets, all colors of light are scattered equally, making clouds appear white.
Red Color of the Sun during Sunrise and Sunset:
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During sunrise and sunset, the sun is near the horizon, and its light must pass through a greater portion of the atmosphere.
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This longer path causes most of the shorter-wavelength blue light to scatter away, leaving the longer-wavelength red light to reach our eyes, making the sun appear red.
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