Phenomena of atmospheric refraction

in this ppt there is info about atmospheric refraction.info about scattering of light, rainbow formation, twinkling of stars, cause of refraction of light,laws of refraction, why the sky is blue, why the sun appears red at sunrise and at sunset, why clouds appear white are also given.

1. VARIOUS PHENOMENA BASED ON ATMOSPHERIC REFRACTION

2. CLASS 10 TH LOTUS GROUP NUMBER

3. ACKNOWLEDGEMENT I would like to thank my Science teacher Shalini M am and my group members for helping me in making this presentation. M y group members helped me in editing of this presentation. M y parents helped me in formatting the matter of the presentation. I collected the information from the internet and from some books.My other gratitude I would like to convey to my school who suggest me to make this and to have marks for adding it into examination.

4. CONTENT

5. REFRACTION The change in the direction of light when it passes from one medium to another, is called Refraction o f light. In other words, the bending of light when it goes from one medium to another obliquely is called Refraction of light-

6. CAUSE OF REFRACTION OF LIGHT The refraction of light is due to the change in the speed of light on going from one medium to another. Greater the difference in the speeds of light in the two media, greater will be the amount of refraction of light.

7. LAWS OF REFRACTION The refraction of light on going from one medium to another takes place from one medium to another takes place according to two laws which are known as Laws of Refraction . These are:- The incident ray, the normal ray, and the point of incidence, all lie in the same plane. The ratio of sine of incidence to the sine of refraction is a constant for the light of a given colour and for the given pair of media. This is also known as Snell’s Law of refraction . If i is angle of incidence and r is the angle of refraction, then Sin i/ sin r = constant

8. ATMOSPHERIC REFRACTION In the A tmosphere we have several layers having different optical densities. The refraction of light caused by earth’s atmosphere having layers of air of varying optical densities is called A tmospheric Refraction .

9. TWINKLING OF STARS The twinkling of stars is due to the atmospheric refraction of star’s light. When the light coming from a star enters the earth’s atmosphere, It undergoes refraction due to the varying optical densities of air at various altitudes. The continuously changing atmosphere refracts the light from the stars by different amounts from one moment to the next. The star light reaching our eyes increases and decreases continuously due to atmospheric refraction. And the star appears to twinkle at night.

10. ADVANCE SUNRISE AND DELAYED SUNSET When the sun is slightly below the horizon, then the sun’s light coming from less dense air to more dense air is refracted downwards as it passes to the atmosphere. Because of this atmospheric refraction, the sun appears to be raised above the horizon when actually it is below the horizon. The same is in the case of delayed sunset. It is due to the atmospheric refraction, we see the sun for 4 minutes extra.

11. The raindrops in the atmosphere act like many small prisms. When sunlight enters a rain drop, it refracts inside the drop. Then it strikes the boundary between two media (which is known as total internal reflection) and disperses. This light is reflected off backside of raindrop at critical angle. It takes many different raindrops to produce a rainbow. RAINBOW FORMATION

12. SCATTERING OF LIGHT Scattering of light occurs when light is deflected in all directions. Scattering of light occurs when light bounces on colloidal particle and particles large than colloidal particles. It is also called Tyndall effect. Blue skies and red suns are due to scattering of light.

13. WHY THE SKY IS BLUE The sunlight is made up of seven colours. When sunlight passes through the atmosphere, most of the lights of longer wavelengths such as red, yellow, orange etc. present in it do not scattered much by air molecules and hence pass straight through. However the shorter wavelengths scattered all around the sky by air molecules in the atmosphere. That is why the sky appears blue.

14. WHY SUN APPEARS RED AT SUNRISE AND SUNSET The sun and the surrounding sky appear red at sunrise and sunset because at that time most of the blue colour has been scattered out and away from our eyes, leaving behind mainly red colour in the direct sunlight beam that reaches our eyes.

15. WHY THE CLOUDS APPEAR WHITE When the particles are large, the scattering of light cause the particles to be look as white. Some light penetrates to cloud base and white light is scattered in all directions. That is why cloud appears as white

16. T H A N K Y O U