Scattering of light

2.  KERALA UNIVERSITY COLLEGE OF TEACHER EDUCATION
 KOLLAM

3. SCATTERING OF LIGHT

4. SCATTERING OF LIGHT
Scattering is a general physical
process whereby some forms of
radiation such as light or moving
particles, for example, are forced to
deviate from a straight trajectory by
one or more localized non-uniformities
in the medium through
which it passes.

6.  A large number of molecules are present
in the earth’s atmosphere. These
molecules scatter light in various
directions. The air is composed of many
tiny particles including dust and water
vapour. As the sunlight passes through
the air, the shorter blue light waves are
reflected and refracted by the particles
while the other coloured light waves being
longer are unaffected and are not
reflected by the water vapour or dust in
the air.

8.  When light passes through a substance or gas, a part of it
is absorbed and the rest scattered away. The basic
process in scattering is absorption of light by the
molecules followed by re-radiation in different directions.
The strength of scattering can be measured by the loss of
energy in the light beam as it passes through the
medium. In absorption the light energy is converted into
the internal energy of the medium and in scattering the
light energy is radiated in other directions. The strength of
scattering depends on the size of the particle causing
the scattering and the wavelength of light. The scattering
is proportional to 1/h4. This is known as Raleigh's law of
scattering. So the red light is scattered the least and the
violet is scattered the most. This explains why red signals
are used to indicate danger.

10. BLUE COLOUR OF SKY

11. The blue color of the sky is due to Rayleigh
scattering. blue sky As light moves through the
atmosphere, most of the longer wavelengths pass
straight through. Little of the red, orange and
yellow light is affected by the air.
However, much of the shorter wavelength light is
absorbed by the gas molecules. The absorbed
blue light is then radiated in different directions. It
gets scattered all around the sky. Whichever
direction we look, some of this scattered blue
light reaches to us. Since we see the blue light
from everywhere overhead, the sky looks blue.

12. YELLOW COLOUR OF SUN

13. SUN IS YELLOW DURING SUNSET AND SUN
RISE
• After the much of the blue portion of
the white light spectrum is absorbed by
the molecules in the atmosphere, the rest
of the spectrum continues on its journey.
Because the blue element has been
removed from the spectrum, the
remaining components combine to
appear yellow or golden to the naked
eye.

14. WHITE COLOUR OF CLOUDS

15. Clouds appear white because the light coming from the sun has
to pass through the water droplets and ice crystals or we can say
that the seven colors of visible spectrum (red, orange, yellow,
green, blue, indigo, violet) which when combines forms white
light and this process of combining is done by water droplets or
ice crystals present in the clouds. On the whole we can say that
light is reflected in many ways which combines to give white
color .