Experience the Human Eye and the Colourful World Like Never Before
The human eye is an incredible part of the body and allows us to explore the colourful world around us. Through notes, chapter 10, we can learn about the light-sensing cells of the eye and how they help us to process the colourful world around us. This knowledge can help us to understand and appreciate the beauty of the world around us.
Our class 10 science notes provide students with the best way to learn and understand science topics. Our science notes come in PDF format, making them easy to download and study. With our notes, students can explore the fascinating workings of the human eye and the vast array of vibrant colours that make up our world.
Our website provides PDF downloads for CBSE Class 10 Science students. Specifically, the PDFs cover topics such as the human eye and the colourful world. These PDFs provide a comprehensive overview of the subject matter and are perfect for studying and revising for exams. Additionally, the PDFs are free to download and can be accessed from any device. Get the latest CBSE Class 10 Science PDFs and get ready to ace your exams
THE HUMAN EYE AND THE COLOURFUL WORLD
Human eye
The human eye makes use of light to allow us to view the world around us. Its structural design includes a lens.
The human eye is like a camera. Its lens system forms an image on a light-sensitive screen called the retina. Light enters the eye through a thin membrane called the cornea.
The eyeball is approximately spherical in shape with a diameter of about 2.3 cm.
The crystalline lens merely provides the finer adjustment of focal length required to focus objects at different distances on the retina. We find a structure called iris behind the cornea. Iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering the eye. The eye lens forms an inverted real image of the object on the retina.
Accommodation:
The ability of the eye lens to adjust its focal length is called accommodation. Focal length can be changed with the help of ciliary muscles.
Far point
The maximum distance at which object can be seen clearly is far point of the eye. For a normal adult eye, its value is infinity.
Near point
The minimum distance at which objects can be seen most distinctively without strain.
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For a normal adult eye, its value is 25 cm.
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Range of human vision 25 cm to infinity.
Myopia (Near sightedness)
A myopic person can see nearby objects clearly but cannot see distant objects clearly. The image of distant object is formed in front of the retina.
Causes of Myopia
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Excessive curvature of eye lens
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Elongation of eye ball
Correction
This defect can be corrected by using a concave lens of suitable power.
A concave lens of suitable power will bring the image back on to the retina and thus the defect is corrected.
Hypermetropia (Far sightedness)
Affected person can see far objects clearly but cannot see nearby objects clearly.
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The near point of the eye moves away.
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Image is formed behind the retina.
Causes of Hypermetropia
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Focal length of the eye lens becomes too long.
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Eye ball becomes too small.
Correction
Use of convex lens of suitable power can correct the defect.
Presbyopia (Old age Hypermetropia)
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It is the defect of vision due to which an old person cannot see the nearby objects clearly due to loss of power of accommodation of the eye.
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The near-point of the old person having presbyopia gradually recedes and becomes much more than 25 cm away.
Causes
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Gradual weakening of ciliary muscles.
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Diminishing flexibility of eye lens.
Correction
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Use of convex lens of suitable power.
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Sometimes a person may suffer from both myopia and Hypermetropia.
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Such people require bifocal lens for correction.
Refraction of light through a prism
It 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.
Angle of deviation (D):
It is the angle between incident ray and emergent ray.
Dispersion -
When white light is passed through a glass prism, it splits into its seven constituent colours to form a band of seven colours. This phenomenon is called dispersion.
Spectrum:
The band of seven colours formed due to dispersion of white light is called spectrum.
Acronym:
It is a group of alphabets that represent sequential colours in spectrum.
V I B G Y O R (violet, indigo, blue, green, yellow, orange and red)
Rainbow:
It is a natural spectrum appearing in the sky after rain showers.
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Rainbow is observed in the direction opposite to the sun.
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Three phenomenon which are involved in rainbow formation are:
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Dispersion
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Refraction
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Internal reflection
Some water droplets remain suspended in air after rain. These droplets behave as glass prism. When light enters the rain drop, it first refracts and disperses. Then it reflects internally and again refracts as it come out of the drop and the seven colours reach the eye of observer in form of rainbow.
Atmospheric Refraction
​The earth's atmosphere is not uniform throughout, its density goes on changing as we move up or down, it can be considered to be consisted of layers of different densities, which act as rarer or denser medium with respect to each other. The refraction of light due to these layers is called atmospheric refraction.
Some phenomena based on atmospheric refraction are
Twinkling of stars
Is due to atmospheric refraction of star's light. As the light from the star enters the earth's atmosphere, it undergoes refraction due to varying optical densities of air at various altitudes. The continuously changing atmosphere refracts the light by different amounts. In this way, the star light reaching our eyes increases and decreases continuously and the stars appears to twinkle at night.
Advance sunrise and delayed sunset
This is because of atmospheric refraction. When the sun is slightly below the horizon, the sun's light coming from less dense to more dense air, is refracted downwards. Because of this, the sun appears to be raised above the horizon.
Scattering of Light
The reflection of light from an object in all directions is called scattering of light. The colour of scattered light depends on the size of scattering particles. Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths. Some phenomena based on scattering of light are given below.
Tyndall effect
The path of a beam of light through a true solution is not visible. However, its path becomes visible when it passes through a colloidal solution, where the size of the particles is relatively larger.
This scattering of light when it passes through a colloidal solution is called Tyndall effect. The earth's atmosphere is a heterogeneous mixture of minute particles of smoke, tiny water droplets due to suspended particles of dust and molecules of air. Tyndall effect becomes visible due to scattering of light.
Colour of the sky
During the day time, sky appears blue. This is because the size of the particles in the atmosphere is smaller than the wavelength of visible light, so they scatter the light of shorter wavelengths (blue end of spectrum) and hence, the sky appears blue. It should be noted that the sky appears black to the passengers flying at higher altitudes because scattering of light is not prominent at such height due to the absence of particles.