Physics seminar class 10
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Slide 1 - Human Eye and Colourful World
- Physics Seminar
Slide 2 - The Members
- Human eye
- Defects of vision
- Refraction through a prism
- Dispersion of white light in prism
- Atmospheric refraction
- Scattering of light
- Nathaniel Sam George
- Abhinav S Nair
- Gladin G Benny
- Johan V Zechariah
- Topics we’re about to cover:
Slide 3 - Human Eye
Slide 4 - Human eye in detail:
- Diagram of an eye
- 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. On closing the eyes, we can identify objects to some extent by their smell , taste, sound they make or by touch. It is, however, impossible to identify colours while closing the eyes. Thus, of all the sense organs, the human eye is the most significant one as it enables us to see the beautiful, colourful world around us.
- 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. It forms the transparent bulge on the front surface of the eyeball .
Slide 5 - Facts on human eye!!
- Did you know?
- A human eye is far better than a camera in case of pixels , because our eye has the capacity of 570 MP ( Mega Pixel) when a camera doesn’t cross beyond 45 MP!!
- Didn’t you know?
- Our eyes are located in front of our face. One eye provides 150° wide field of view while both eyes simultaneously provide 180° wide field of view. It is the importance of the presence of two eyes as both eyes together provide the three-dimensional depth in the image.
Slide 6 - Functions of parts of eye :
- The outer part of the eye is quite tough and white in colour. This white part of the eye is known as sclera.
- The transparent, front outer covering of the eye is known as the cornea.
- Behind the cornea, there is a colored membrane known as the iris. It regulates the amount of light entering the eye. It also gives colour to the eye.
- In the iris, there is a variable sized, black circular opening known as the pupil. Its size is controlled by the iris. It appears to be black in colour because most of the light entering it is absorbed by the tissues, which are present in the pupil.
Slide 7 - Defects of Eye
- We can see distant objects as well as the objects near us. The minimum distance up to which an eye can see clearly and distinctly without any stress is called the least distance of distinct vision.
- The least distance of distinct vision for a normal eye is 25 cm.
- The defects of eye also include problems like:
- Defects of Eye
Slide 8 - Myopia
- Myopia is a defect of vision in which a person clearly sees all the nearby objects, but is unable to see the distant objects comfortably and his eye is known as a myopic eye. A myopic eye has its far point nearer than infinity. It forms the image of a distant object in front of its retina.
Slide 9 - Myopia , Causes and Correction
- Myopia is caused by
- increase in curvature of the lens
- increase in length of the eyeball
- 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 form at the retina by using a concave lens of suitable power as shown in the given figure.
Slide 10 - Hypermetropia (Long sightedness)
- Hypermetropia is a defect of vision in which a person can see distant objects clearly and distinctively, but is not able to see nearby objects comfortably and clearly.
Slide 11 - Hypermetropia ,Causes and Correction
- Hypermetropia is caused due to
- Reduction in the curvature of the lens
- Decrease in the size of the eyeball
- 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.
Slide 12 - Presbyopia
- Presbyopia is a common defect of vision, which generally occurs at old age. A person suffering from this type of defect of vision cannot see nearby objects clearly and distinctively. A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older.
Slide 13 - Presbyopia , Causes and Correction
- Presbyopia is caused by the:
- Weakening of the ciliary muscles.
- Reduction in the flexibility of the eye lens
- A person with presbyopia cannot read letters without spectacles. It may also happen that a person suffers from both myopia and hypermetropia. This type of defect can be corrected by using bi-focal lenses. A bifocal lens consists of both convex lens (to correct hypermetropia) and concave lens (to correct myopia).
Slide 14 - Astigmatism:
- Astigmatism, a defect in the outer curvature on the surface of the eye that causes distorted vision. In astigmatism, a person cannot simultaneously focus on both horizontal and vertical lines.
- Using cylindrical lens.
Slide 15 - Refraction by a Prism
- The separation of visible light into its different colors is known as dispersion.
- The amount of overall refraction caused by the passage of a light ray through a prism is often expressed in terms of the angle of deviation . The angle of deviation is the angle made between the incident ray of light entering the first face of the prism and the refracted ray that emerges from the second face of the prism. Because of the different indices of refraction for the different wavelengths of visible light, the angle of deviation varies with wavelength. Colors of the visible light spectrum that have shorter wavelengths (BIV) will deviated more from their original path than the colors with longer wavelengths (ROY). The emergence of different colors of light from a triangular prism at different angles leads an observer to see the component colors of visible light separated from each other.
- Refraction by a Prism
Slide 16 - Refraction Through a Prism
- Refraction of prism is explained through this video:
Slide 17 - Formation of Rainbow
- Formation of rainbow is explained through this video:
Slide 18 - Atmospheric Refraction
- Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of altitude.
- Flickering of objects on hot air.
- Twinkling of stars.
- Early sun rise and delayed sunset.
Slide 19 - Flickering of objects on hot air.
- The movements of hot and cold air results in the variation in the refractive index of the atmosphere. This makes objects flicker as in the image below:
Slide 20 - Twinkling of stars:
- Stars twinkle when we see them from the Earth's surface because we are
- viewing them through thick layers of moving air in the earth's atmosphere.
- Stars (except for the Sun) appear as tiny dots in the sky; as their light
- travels through the many layers of the Earth's atmosphere, the light of the
- star is bent (refracted) many times and in random directions. This random
- refraction results in the star twinkling at us. It looks as though the star
- moves a bit, and our eye interprets this as twinkling.
- Stars closer to the horizon appear to twinkle more than stars that are
- overhead - this is because the light of stars near the horizon has to travel
- through more air than the light of stars overhead and this is subject to
- more refraction. Also, planets do not usually twinkle, because they are so
- close to us; they appear big enough that the twinkling is not noticeable.
- Stars would not appear to twinkle if we viewed them from outer space or
- from a planet/moon that didn't have an atmosphere.
Slide 21 - Early Sunrise and Delayed Sunset
- Explained in the video below
Slide 22 - Scattering of light
- Light scattering is a form of scattering in which light is the form of propagating energy which is scattered. Light scattering can be thought of as the deflection of a ray from a straight path, for example by irregularities in the propagation medium, particles, or in the interface between two media.
- Tyndall Effect
- Blue colour of sky
- Reddish Sky
- Scattering of light.
Slide 23 - Tyndall Effect
- The Tyndall effect, also known as Tyndall scattering, is light scattering by particles in a colloid or particles in a fine suspension. It is named after the 19th-century physicist John Tyndall.
- Because a colloidal solution or substance (like fog) is made up of scattered particles (like dust and water in air), light cannot travel straight through. Rather, it collides with these micro-particles and scatters causing the effect of a visible light beam. This effect was observed and described by John Tyndall as the Tyndall Effect.
- The Tyndall effect is an easy way of determining whether a mixture is colloidal or not. When light is shined through a true solution, the light passes cleanly through the solution, however when light is passed through a colloidal solution, the substance in the dispersed phases scatters the light in all directions, making it readily seen.
Slide 24 - Appearance of sky as blue
- Explained in the video below
Slide 25 - Reddish Sunsets
- The lower frequencies of sunlight (ROY) tend to reach our eyes as we sight directly at the sun during midday. While sunlight consists of the entire range of frequencies of visible light, not all frequencies are equally intense. In fact, sunlight tends to be most rich with yellow light frequencies. For these reasons, the sun appears yellow during midday due to the direct passage of dominant amounts of yellow frequencies through our atmosphere and to our eyes.
- The appearance of the sun changes with the time of day. While it may be yellow during midday, it is often found to gradually turn color as it approaches sunset. This can be explained by light scattering.
Slide 26 - Vote of Thanks
- We thank everyone for being so calm for listening us and we also thank Kiran sir for giving us leave to make this PowerPoint Presentation.
- Thank You…