The refractive index
The refractive index
The refractive index:--
When a ray of light travels from one transparent medium
into another medium, the change of direction takes place in a given pair of
media is called as refractive index.
the refractive index can be linked with the important
physical quantity, the relative speed of propagation of light in different
media. It means speed of light propagates
with different speeds in different media. Speed of light is faster in vacuum
with speed of 3 * 108 meters/second. but in the air, the speed
of light is 2.98 * 108 meters/second.
It means speed of light in air is
compared less as compared with speed of light in the vacuum. And the speed of
light in glass and water is less than the speed of light in vacuum.
The refractive index determine the path of light is bent or
refracted, when entering any medium.
The refractive index is expressed as the degree of the change of direction of the light in two medium.
The value of the refractive index in the given pair of media
is depends upon the speed of light in the two media. Or we can say that the
value of the refractive index change in
a medium is depends upon the property of the medium.
Suppose that a ray of light is passing from medium 1 to
medium 2.
Here, in medium 1 , the speed of light is --- v1
In medium 2 , the speed of light is – v2
The refraction index of the medium 2 with respect to the
medium 1 is given by the ratio of the speed of the light in medium 1 that is (v1) and the speed of light in medium 2 that is (v2)
This equation can be expressed as :--
Speed
of light in medium 1 v1
n21= ……………………………
= ………………………
speed
of light in medium 2
v2
or we can say that the refractive index of medium 1 with respect to the medium 2 is
denoted as n12.
This equation can be expressed as :--
Speed
of light in medium 2 v2
n12 = ……………………………
= ………………………
speed
of light in medium 1
v1
the absolute refractive index
when light travels from vacuum or air to another medium then the
refractive index is called as absolute refractive index.
It means to say that the medium 1 is considered as air or
vacuum then the refractive index of the medium 2 is to be considered with
respect to vacuum. This is known as absolute refractive index.
The speed of light in air is ---- c
The speed of light in the medium is ---- v
The refractive index is denoted by nm
The refractive index is expressed as:--
Speed of
light in air c
nm =…………………………. ………………… = ……….
Speed of
light in the medium v
Point to be noted
that—an optically denser medium may not possess greater mass density.
Example:-- kerosene have higher refractive index. So kerosene
is optically denser than the water. But kerosene
has less mass density than water.
Example:- the refractive index of water is nw=
1.33.
This means that the ration of the speed of the light In air
and the speed of light in water is equal to the 1.33.
Light is travelling 1.33 times slower in water than in
vacuum.
So increasing the refractive index corresponds to the
decreasing the speed of the light in the materials.
Optical density :--
The ability of the
medium to refract the ray of light is expressed as optical density.
Optical density has a definite connotation.
Optical density is not the same as mass density.
Here , when a ray of light travels from the terms rarer
medium and denser medium. It means to say that it is optically rarer medium and
optically denser medium.
Here, when we say that the medium is optically denser than
the other among the two medium. Then one with larger refractive index is
optically denser medium than the other.
And the other with lower refractive index is optically rarer
medium.
The speed of light is higher in a rarer medium than the
denser medium.
So that , the ray light is travelling from the rarer medium
to denser medium, then the speed of light slows down and bends towards the
normal.
The ray of light from denser medium to rarer medium , then
the speed of light increases and bends away from the normal.
Optical density is the property to measure the speed of
light through the material.
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