Class 10, Science, Chapter-9, Lecture-9, Scattering (Notes)
SCATTERING OF LIGHT:
The change in path of components of polychromatic light in different directions caused due to reflection, refraction or internal reflection is termed as scattering of light.
TYNDALL EFFECT:
The visibility of the path of light due to scattering of light by the particles of a colloidal medium is termed as Tyndall effect.
Relation Between Size of Particles and Colour of Scattered Light:
Size of Particles | Colour of Scattered Light |
Very small | Blue |
Large | Red |
Very large | White |
REASON FOR BLUE COLOUR OF SKY:
The colour of the scattered light depends on the size of the particles.
The particles present in the atmosphere are very small and therefore scatter blue light (shorter wavelength) and do not scatter red light.
The scattered blue light reaches our eyes.
Hence the sky looks blue.
In the absence of atmosphere, Sky would be dark.
Reason:
The blue colour of the sky is due to scattering of blue light by the small particles present in the atmosphere.
In the absence of the atmosphere, no scattering will take place.
As the light is invisible, so the sky would look dark.
‘DANGER’ signal lights are RED in colour.
Reason:
The colour of the scattered light depends on the size of the particles.
The particles present in the atmosphere are very small and therefore scatter blue light (shorter wavelength) and do not scatter red light.
This makes red light visible from large distances.
So, ‘danger’ signal lights are red.