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LIGHT-HUMAN EYE AND THE COLOURFUL WORLD-converted.pptx
- 1. THE HUMAN EYE AND THE COLOURFUL WORLD Chapter-11 For Class-X By Sri. SIDDALINGESHWARA BP M.Sc, B.Ed, (P.hd) Sandeepani Naional Public School SH-76, Gejjegondanahalli, Ajjampura-577545
- 2. Content: 1. Refraction of light through a glass prism 2. Dispersion of white light by a glass prism 3. Recombination of white light Rainbow 4. Atmospheric Refraction i) Twinkling of stars ii) advanced sunrise and delayed sunset. 5 Scattering of light i) Tyndall effect ii) Way the colour of sky is blue? iii) Colour of sun at sunrise and sunset
- 3. 1. Refraction of light through a glass prism: Prism is a transparent refracting medium bounded by two lateral surfaces, inclined to each other at a certain angle. It has two triangular bases and three rectangular lateral surfaces. The angle between two lateral surface is called angle of prism(A). The angle at which the emergent ray makes with the incident ray is called angle of deviation(D). It depends the angle of the prism. i.e angle of incidence and angle of emergence and is given by 𝐷 = 𝑖 + 𝑒 − 𝐴 Note : Lateral surface : sides of an triangle.
- 4. When a ray of light passes through a glass prism, it gets bent twice at the air- glass interface and glass- air interface. The emergent ray is deviated by an angle to the incident ray.This angle is called the angle of deviation. air Glass air
- 5. Beam of white light Spectrum R O Y G B I V Glass prism When a beam of white light is passed through a glass prism, it is split up into a band of colours called spectrum. This is called dispersion of white light. The spectrum of white has the colours violet, indigo, blue, green, yellow, orange and red (VIBGYOR). The red light bends the least and the violet light bends the most.
- 6. Isaac Newton was the first one to use a glass prism to obtain the spectrum of light.
- 7. Cause of Dispersion: Light rays of different colors, travel with the same speed in vacuum and air but air but in any other medium, they travel with different speeds and bend through different angles, which leads to the dispersion of light. Red light has the maximum wavelength and violet light has the minimum wavelength. Violet maximum deviation and red light minimum deviation. The dispersion discovered by Newton its splitting of white light into 7 colors and also shows that reverse of dispersion of light is also possible and will get the same that is again white light after reverse of dispersion of white light its called Recombination of white light.
- 8. R V V R R Glass prisms When a beam of white light is passed through a glass prism, it is split up into its component colours. When these colours are allowed to fall on an inverted glass prism it recombines to produce white light. V White light White light
- 9. A rainbow is a natural spectrum appearing in the sky after a rain shower. It is caused by the dispersion of sunlight by water droplets present in the atmosphere. The water droplets act like small prisms. They refract and disperse the sunlight then reflect it internally and finally refract it again when it comes out of the rain drops. Due to the dispersion of sunlight and internal reflection by the water droplets we see the rainbow colours. Rainbow apperes opposite to the sun light and observer. Red colour appears on the upper side of rainbow and Raindrop Violet Sunlight Refraction and dispersion Internal reflection Observer Refraction Red
- 11. Eye Atmospheric refraction is due to the gradual change in the refractive index of the atmosphere. The refractive index of the atmosphere gradually increases towards the surface of the earth because the hot air above is less dense than the cool air below. So light gradually bends towards the normal. So the real position of a star is different from its apparent position. The refractive index of hot air is less than cool air. This is because cold air is more denser then hot air. Any way its depends on temperature. Apparent position Star Real position Increasing refractive index of atmosphere 5. Atmospheric Refraction:
- 13. The twinkling of stars is due to the atmospheric refraction of star light and due to the changing in the position of the stars and the movement of the layers of the atmosphere. So the light from the stars is sometimes brighter and sometimes fainter and it appears to twinkle. Planets are closer to the earth than stars. The light from stars are considered as point source of light and the light from planets are considered as extended source of light. So the light from the planets nullify the twinkling effect.
- 15. Earth Observer Sunrise Sunset Apparent position Apparent position Atmosphere ii) Advance sunrise and delayed sunset The sun is visible to us about 2 minutes before sunrise and about two minutes after sunset due to atmospheric refraction. The apparent flattening of the sun’s disc at sunrise and at sunset is also due to atmospheric refraction. Horizon Horizon Real position Real position
- 16. i) Tyndall effect :- When a beam of light passes through a colloidal solution, the path of light becomes visible due to the scattering of light by the colloid particles. This is known as Tyndall effect. The earth’s atmosphere contains air molecules, water droplets, dust, smoke etc. When sunlight passes through the atmosphere the path of the light becomes visible due to the scattering of light by these particles. The colour of the scattered light depends upon the size of the scattering particles. Very fine particles scatter blue light. Larger particles scatter different colours of light.
- 17. The fine particles in the atmosphere have size smaller than the wave length of visible light. They can scatter blue light which has a shorter wave length than red light which has a longer wave length. When sunlight passes through the atmosphere, the fine particles in the atmosphere scatter the blue colour more strongly than the red and so the sky appears blue. If the earth had no atmosphere there would not be any scattering of light and the sky would appear dark. The sky appears dark at very high altitudes. ii) Why the colour of sky is Blue?
- 18. At sunrise and at sunset the sun is near the horizon and the light from the sun travels through the thicker layers of the atmosphere and longer distance through the atmosphere. Near the horizon most of the blue light and shorter wave lengths are scattered away by the particles of the air and the red light and longer wave lengths reaches our eyes. So the sun appears reddish at sunrise and sunset. Observer Sun overhead Blue light scattered away Sun appears reddish Sun near horizon Atmosphere Earth Horion: The line at which the earth’s surface and the sky appear to meet
- 19. References: 1. NCERT Text book 2. Google Sources 3. Slide share Avoid LIGHT POLLUTION (PHOTO POLLUTION): Light pollution, unwanted or excessive artificial light. Like noise pollution, light pollution is a form of waste energy that can cause adverse effects and degrade environmental quality.