Scattering of Light
The scattering of light is an important observation in our daily life. The way light scatters off molecules in the atmosphere explains why the sky is blue and why the sun looks red at sunrise and sunset. This is because of the scattering of light.
A beam of light or laser, invisible in clear air or pure water, will trace a visible path through colloidal particles. This is known as the Tyndall effect after its discoverer, the 19th-century British physicist John Tyndall. The colour of the scattered light depends on the size of the particles. The very fine particles scatter colours of all wavelengths . The large particles in size scatter colours of longer wavelengths. The examples are * A headlight on a car shining through fog.
* A fine beam of sunlight entering a smoke filled room through a small hole. * When sunlight passes through a canopy of a dense forest. Why is the Colour of the Clear Sky Blue?
The colour of the clear sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.The white light from the sun is a mixture of all colours of VIBGYOR. The colours of light are distinguished by their different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between. According to Rayleigh Scattering law, the scattering of light is inversely proportional to the fourth power of its Wavelength.
| Light from the Sun near the horizon passes through thicker layers of air and larger distance so it appears red. At noon, the Sun appears White as only a little of the blue and violet colours are scattered.
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