Define Scattering of Light Class 10

In this article, we will discuss about what is scattering of light? , Rayleigh's law, why does the sky appear blue and examples of scattering of light, important question, important questions for class 10 science and much more. We will Define Scattering of Light Class 10 here.

Define Scattering of Light

What is scattering of light?

            (Or)

Define Scattering of Light Class 10.

Scattering of light

    As sunlight enters the earth's atmosphere, the nitrogen and Oxygen molecules of air absorb some amount of sunlight and re-emit it. The free gas molecules scatter light in all directions, But scattering is preferential.

Define Scattering of Light

Rayleigh's law of scattering shows the intensity of scattered light,

`I \prop \frac{1}{\lamda^4}`

Examples of scattering of light 

Blue color of clear sky

   The cause of the blue color of the clear sky is the scattering of sunlight by the molecules of the atmosphere. As sunlight enters the earth's atmosphere, the nitrogen and Oxygen molecules of air absorb some amount of sunlight and re-emit it. The free gas molecules scatter light in all directions, But scattering is preferential. Rayleigh's law of scattering shows the intensity of scattered light,

`I \prop \frac{1}{\lamda^4}`

    So the light at the short wavelength (blue) end of the visible spectrum is scattered about ten times more than the light at long wavelength (red) end. When we look at the sky, the scattered light enters our eyes and this light contains blue color in larger proportion. That is why the clean sky appears blue.

    If the earth have no atmosphere, there would be no scattering of light, the sky would appear black and stars could be seen during day hours. This is what astronauts actually observe at heights 20 km above the earth surface where the atmosphere becomes quite thin or on the moon which has no atmosphere. 

At the time of sun-rise and sun-set the Sun appears to be reddish :

According Rayleigh's scattering law, the intensity of scattered light is, 

`I \prop \frac{1}{\lamda^4}`

Clearly, The waves whose wavelength is more, the scattering of those light rays is less, that is, those light rays spread less and the light waves which have less wavelength, their scattering is more. Due to this scattering, the light rays with less wavelength spreads more.

 When the sun is near the horizon at sunset or sunrise, the light rays have to traverse a larger thickness of the atmosphere than when the sun is overhead at noon. Due to the high wavelength of red color, its scattering is very less, due to which the red color spreads less and reaches our eyes directly, that is why the sun appears red to us. Hence the sun appears almost reddish at sunset and sunrise.

Red signals

    According to Rayleigh's scattering law, the intensity of scattered light,

`I \prop \frac{1}{\lamda^4}`

Clearly, smaller the wavelength, more is the scattering. Since the wavelength of red color is the most, hence its scattering will be the least. As a result, red color is seen up to far distances. That is why the danger signals are red in color.

Clouds are generally seen in white

    There are dust particles and water drops in clouds and their size is much more than the wavelength of light (a>>>`\lamda`), therefore they do not scatter the light according to Rayleigh's law, and their scattering is not selective. They scatter light of all colors almost equally. Hence the clouds having droplets of water with a>>>`\lamda`, are generally seen as white.

What is scattering of light?

    Scattering is the phenomenon of light being scattered in different directions after colliding with the particles of the atmosphere. 

    Due to the phenomenon of scattering, we see the blue color of the sky and when the light falls on the surface of the water, then we see sparkles of sunlight on the surface of the water.

    The waves whose wavelength is more, the scattering of those light rays is less, that is, those light rays spread less and the light waves which have less wavelength, their scattering is more. Due to this scattering, the light rays with less wavelength spreads more. The wavelength of blue color is less, due to which the scattering of blue color is more, that is, it spreads more, that is why the color of the sky appears blue.

Here are a few examples of scattering of light in our everyday lives :

Blue sky: The waves whose wavelength is more, the scattering of those light rays is less, that is, those light rays spread less and the light waves which have less wavelength, their scattering is more. Due to this scattering, the light rays with less wavelength spreads more. The wavelength of blue color is less, due to which the scattering of blue color is more, that is, it spreads more, that is why the color of the sky appears blue.

Sunset and Sunrise: At sunrise or sunset when the sunlight has to travel more distance to cross the Earth's atmosphere. The wavelength of red color is the highest, due to which the scattering of red color is less and red color spreads less in the sky and covers more distance and reaches our eyes, due to which the sun appears red at sunrise and sunset. Due to the low wavelength of other colors, they get scattered due to which these colors get scattered and cannot travel much distance and reach our eyes. This is the reason for the reddish sun and the sky.

Sparkling Water: When sunlight is incident on the surface of water, the phenomenon of scattering occurs due to which the light gets scattered in all directions. Due to this the surface of the water appears shining.

Fog and haze: When the size of the particles of the medium is more than the wavelength of the light past you, then the phenomenon of scattering occurs, this scattering is called non-selective scattering. Due to this scattering, the light gets scattered equally in all directions.

Why does red light scatter less?

According to Rayleigh scattering, the efficiency of scattering is inversely proportional to the fourth power of the wavelength.

`I \prop \frac{1}{\lamda^4}`

    Sunlight is white in which blue color has the lowest wavelength (about 4000) and red color has the highest wavelength (about 8000), due to which blue color is scattered the most and red color is least scattered. The wavelength of red is twice as long as that of blue, due to which the scattering of red is 16 times less.

Is rainbow an example of scattering of light? Explain.

After some time of rain, small drops of water keep floating in the sky, when sunlight is incident on these drops, then the phenomenon of refraction, total internal reflection and dispersion of color takes place in the light. Due to this a strip of colors (7 colors) appears simultaneously in the sky which is called rainbow.

The phenomenon of scattering does not take place in the formation of a rainbow.

Important Questions :

FAQs

Q. What is scattering of light?

Q. Why is the Sky Blue?

Q. Explain, The Mystery of Red Sunrises and Sunsets.

Q. Why Danger Signals are Always in Red Color"?