e.g. red light, violet light, blue light, etc.
* Polychromatic light- Light consisting of more than
two colours or wavelengths is called polychromatic
light.
e.g. white light
Recombination of white light
-> When an inverted prism is placed in the path of
dispersed light then after passing through the prism
then they recombine and form white light.
Issac Newton was was the first person who obtained
spectrum of sunlight by using glass prism.
He tried to split the spectrum of white light
using another similar prism, but he could not get any
more colours. then, He repeated the experiment using
second prism in inverted position with respect to the
first prism. It allowed all the colours of spectrum to
pass through second prism.
As a result, He found that
white light emerges on the other side of second prism.
Rainbow
-> A rainbow is produced by the dispersion of white
light with the help of raindrops which present in the
atmosphere.
The rainbow is actually a natural spectrum of sunlight
in the sky.
It is formed in the sky when the sun is
shining and it is raining at the same time. A rainbow
is always formed in an opposite direction that of the
sun.
Formation of a rainbow
-> The raindrops present in the atmosphere act like
small prisms. A Ray of white sunlight enters in the
raindrop from a point and undergoes refraction and
dispersion to form a spectrum. This spectrum
undergoes total internal reflection at a certain point
within the raindrop and finally refracted out of the
rain drop at a certain point. This spectrum produced
by the raindrops in the atmosphere is seen from the
earth.
The red colour of spectrum appears at the top
of the rainbow whereas violet colour appears at the
bottom of the rainbow.
At 'A' - refraction and dispersion take place
At 'B' - internal reflection takes place
At 'C' - refraction and dispersion take place
Atmospheric Refraction
-> The refraction of light caused by the Earth’s
atmosphere is called Atmospheric Refraction.
Explanation- All the air in the atmosphere is not at the
same temperature. Some of the air layers of the
atmosphere are cool whereas other air layer of the
atmosphere are comparatively hot. So, various air
layers act as various optical densities.
The cooler air layers of the atmosphere behaves as
optically denser medium for lighter whereas the
warmer air layers of the atmosphere behave as
optically rarer medium for the light rays. So, in the
same atmosphere we have air layers having different
optical densities and when light rays passes through
them then refraction of light takes place by the earth's
atmosphere.
Note:- Under normal circumstances, the air in the
upper atmosphere is optically rarer and the air in the
lower atmosphere is optically denser.
So, as we move down, the medium changes from rarer
to denser.
Q) If we look at objects through the hot air oven of
fire then the objects appear to be moving slightly.
Explain?
-> It is because the air just above the fire becomes
hotter than the air which is further up. This hot air is
optically rarer but the colder air which is further up is
optically denser. So, when we see the objects by the
light coming from them through hot and cold air
layers having different optical densities then the
refraction of light takes place randomly.
As a result,
the objects appear to be moving slightly.
Some e.g. of atmospheric refraction are:-
* Appearance of Star Position ->
Light
coming from the star is refracted when it enters the
earth's atmosphere from vacuum. Air higher up in the
sky is rarer but air present near the earth's surface is
denser. So, as the light from a star comes down, the
dense hair bends the light more. Due to the refraction
of star's light, the star appears to be at higher position
from original position of star.
0 Comments
If you have any queries, Please let us know.