PROJECT

1. PROJECT ON Reflection of light through a prism Dispersion of white light by a glass prism Atmospheric refraction Scattering of light

2. A Refracting Surfaces Eye e i Reflection of light through a prism Prism S R P Q N2 N1

3. white light prism spectrum Dispersion of white light by a glass prism A prism splits the colours of white light into the spectrum. This is called dispersion. Violet light deviates the most, red the least.

4. The phenomenon of splitting a ray of white light into its constituentcolours(wavelengths) is called dispersion and the band of colours fromviolettoredis called spectrum (VIBGYOR). A δr D N δv ROYGB IV White light B C Screen

5. A A Q R S P B C A 2 i + e = A + δ sin (A + δm) μ = 2 sin Refraction of Light through Prism N1 N2 δ D e i r1 O r2 μ Prism Refracting Surfaces δ δm 0 i = e i

6. B’ C’ N A Recombination of spectrum of white light: White light A White light C B

7. RAINBOW

8. Eye Formation of Primary Rainbow Rain drop Sunlight 43º 41º A line parallel to Sun’s ray

9. A rainbow is a natural spectrum which is caused by dispersion of sunlight by tiny water droplets present in the atmosphere after a rain shower. • The incident sunlight with suitable angle of incidence is refracted, dispersed, internally reflected and finally refracted out by the rain drops. • Due to the dispersion and internal reflection, different colours reach the eye of the observer. • A rainbow is always formed in a direction opposite to that of the Sun.There are primary and secondary rainbows. • In the primary rainbow the violet colour is on the inner arc and the red colour is on the outer arc. • In the secondaryrainbow, the sequence of colours is opposite due to two internal reflections inside the rain drops. Secondary Primary

10. Atmospheric refraction Refraction of light by earth’s atmosphere is called atmospheric refraction. Flickering of objects above a fire: The apparent random wavering or flickering of objects can be seen through a turbulent stream of hot air rising above a fire. The air just above the fire becomes hotter than the further up. The hotter air is lighter than the cooler air above it, and has a refractive index slightly less than that of the cooler air. Since the physical conditions of the refracting medium (air) are not stationary, the apparent position of the object, as seen through the hot air, fluctuates. This wavering is therefore due to an effect of atmospheric refraction on a small scale in the local environment.

11. Density of Atmosphere & Refractive index increase Eye Twinkling of Stars: The twinkling of a star is due to atmospheric refraction of starlight. The atmospheric refraction occurs in a medium of gradually changing refractive index. Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position. The star appears slightly higher (above) than its actual position when viewed near the horizon. This apparent position is not stationary, but keeps on changing slightly, since the physical conditions of the earth’s atmosphere are not stationary. Since the stars are very distant, they approximate point-sized sources of light. As the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of light entering the eye flickers- the star sometimes appear brighter, and at some other time, fainter which gives the twinkling effect. Apparent position of the Star Real position of the Star

12. Horizon Earth Why Planets do not twinkle? The planets are much closer to the earth, and are thus seen as extended sources. Since it is the collection of large number of point-sized sources of light, the total variation in the amount of light entering into the eye from all the individual sources will average out to zero, thereby nullifying the twinkling effect. Advance Sunrise and Delayed Sunset: The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction. Apparent position of the Sun Atmosphere Real position of the Sun

13. Horizon Earth Scattering of Light –Blue colourof the sky andReddishappearance of the Sun at Sun-rise and Sun-set: Less Blue colour is scattered Atmosphere Other colours mostly scattered

14. SCATTERING OF LIGHT BY TINY WATER DROPLETS IN THE MIST

15. Tyndall Effect • The earth’s atmosphere is a heterogeneous mixture of minute particles. These particles include smoke, tiny water droplets, suspended particles of dust and molecules of air. • When a beam of light strikes such fine particles, the path of the beam becomes visible. • The light reaches us, after being reflected diffusedly by these particles. • The phenomenon of scattering of light by the colloidal particles gives rise to Tyndall Effect. • Tyndall Effect can be seen when a fine beam of sunlight enters a smoke-filled room through a small hole. In this, scattering of light makes the particles visible. • It can also be seen when sunlight passes through a canopy of a dense forest. In this, tiny water droplets in the mist scatter light. • The colour of the scattered light depends on the size of the scattering particles. • Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths. If the size of the scattering particles is large enough, then, the scattered light may even appear white.

17. Screen S SCATTERING OF LIGHT Conc. Sulphuric acid L1 L2 I Sodium thio sulphate solution (hypo)

18. The molecules of the atmosphere and other particles that are smaller than the longest wavelength of visible light are more effective in scattering light of shorter wavelengths than light of longer wavelengths. The amount of scattering is inversely proportional to the fourth power of the wavelength. (Rayleigh Effect) Light from the Sun near the horizon passes through a greater distance in the Earth’s atmosphere than does the light received when the Sun is overhead. The correspondingly greater scattering of short wavelengths accounts for the reddish appearance of the Sun at rising and at setting. When looking at the sky in a direction away from the Sun, we receive scattered sunlight in which short wavelengths predominate giving the sky its characteristic bluish colour.

19. SCATTERING OF LIGHT BY SMOKE & COLLOIDAL PARTICLES

20. MADE BY AYUSH NANDA CLASS – 10TH