vi.1 Prism Play: Light Phenomena through Refraction Magic

Exploring Light Phenomena: A triangular glass prism 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.

[Dispersion of white light by the glass prism]

Prism Magic and the Wonders of Rainbows	Spectrum: The prism splits white light into a band of colors. The various colors seen are Violet, Indigo, Blue, Green, Yellow, Orange and Red. The band of the coloured components of a light beam is called its spectrum. [Recombination of the spectrum of white light] Light Phenomena: Dispersion – The splitting of light into its component colors is called dispersion. Light Phenomena: Different colors of light bend through different angles with respect to the incident ray, as they pass through a prism. The red light bends the least while the violet the most. Thus the rays of each color emerge along different paths and thus become distinct. It is the band of distinct colors that we see in a spectrum. [Rainbow Formation] Light Phenomena : Isaac Newton was the first to use a glass prism to obtain the spectrum of sunlight. He tried to split the colors of the spectrum of white light further by using another similar prism. However, in the exploration of Light Phenomena, he could not get any more colors. He then placed a second identical prism in an inverted position with respect to the first prism. This allowed all the colors of the spectrum to pass through the second prism. He found a beam of white light emerging from the other side of the second prism. This observation gave Newton the idea that the sunlight is made up of seven colors. Any light that gives a spectrum similar to that of sunlight is often referred to as white light. Rainbow: A natural Light Phenomena,a rainbow is a natural spectrum appearing in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop. Due to the dispersion of light and internal reflection, different colors reach the observer’s eye. [Rainbow]
Atmospheric Refraction in Everyday Observations	Light Phenomena in Motion: Sometimes we notice random wavering or flickering of objects seen through a turbulent stream of hot air rising above a fire or a radiator. The air just above the fire becomes hotter than the air further up. The Phenomenon of Light: Hotter air is lighter (less dense) 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 thus an effect of Light Phenomena in Atmospheric Refraction, a small scale in our local environment. Apparent star position due to atmospheric refraction
Starlight Symphony: Light Phenomena in the Twinkling Dance of Stars and Planets	The twinkling of a star is due to atmospheric refraction of starlight. The Light Phenomena, as starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth. 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. Further, this apparent position of the star 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 Phenomena coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers. Thus the star sometimes appears brighter, and at some other time, fainter, which is the twinkling effect. The planets are much closer to the earth, and are thus seen as extended sources. Planets in our solar system are relatively close to Earth and appear as extended disks rather than point sources of light. The light from a planet is not coming from a single point, so the small changes in direction caused by atmospheric turbulence tend to average out across the planet’s visible disk. As a result, the light Phenomena from planets doesn’t twinkle in the same way as stars do, and they appear as steady, non-twinkling points of light in the night sky.
Brightening Time: Exploring Light Phenomena in Early Sunrises and Late Sunsets Due to Atmospheric Refraction	Light Phenomena at Dawn and Dusk: 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. By actual sunrise, we mean the actual crossing of the horizon by the Sun. Time Difference: The time difference between actual sunset and the apparent sunset is about 2 minutes. The apparent flattening of the Sun’s disc at sunrise and sunset is also due to the same phenomenon. Atmospheric Refraction Effects at Sunrise and Sunset
Light Phenomena: Exploring the Wonders of Scattering in Nature	The interplay of light with objects around us gives rise to several spectacular phenomena in nature. The blue color of the sky, the color of water in the deep sea, the reddening of the sun at sunrise and the sunset are some of the wonderful Light phenomena we are familiar with. The path of a beam of light passing through a true solution is not visible. However, its path becomes visible through a colloidal solution where the size of the particles is relatively larger.
Light Phenomena: Exploring the Tyndall Effect in the Scattering Symphony of Earth’s Atmosphere	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 diffusely by these particles. The Light Phenomena: The phenomenon of scattering of light by the colloidal particles gives rise to the Tyndall effect. This phenomenon is seen when a fine beam of sunlight enters a smoke-filled room through a small hole. Thus, scattering of light makes the particles visible. Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest. Here, tiny water droplets in the mist scatter light. The color 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.

Light Phenomena: Exploring the Science Behind the Blue Hue of the Clear Sky

The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. Light phenomena, such as Rayleigh scattering, become prominent in these conditions.
These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end.
The red light has a wavelength about 1.8 times greater than blue light.
Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue color (shorter wavelengths) more strongly than red.
The scattered blue light enters our eyes.
If the earth had no atmosphere, there would not have been any scattering.
Then, the sky would have looked dark.
The sky appears dark to passengers flying at very high altitudes, as scattering is not prominent at such heights.
The ‘danger’ signal lights are red in color because the red is least scattered by fog or smoke.
Therefore, it can be seen in the same color at a distance.