Optical fibre
It is a optical device which helps in communicating the
signal from one place to another place without any transmission loss. It works
basing on total internal reflection concept.
It has two cylindrical parts where inner one is called core
and the outer one is called cladding. The refractive index of core is more than
that of cladding.
In this device light Ray moves from denser medium to rarer
medium. We shall allow the light Ray to incident in the denser medium in such a
way that at the surface it shall experience total internal reflection. We shall
pass the light Ray into the system with a particular angle so that after going
into the device it will experience total internal reflection. This particular
angle is called angle of launching.
When the light is passed through optical fibre there is no
wastage of energy takes place. The entire input that is given at one end will
automatically reach the other end. It is simply because the entire message is
restricted itself only to the denser medium. As angle of incidence is more than
critical angle the entire light Ray reflects back into the core itself. Thus no
portion of the energy has gone into the cladding and hence there is no wastage
of energy.
Optical Fibre is a very thin, light weighted and a flexible
device. It is a part of a nanotechnology such that the size of this device is
very small. Hundreds of optical fibres tied together will just take the size of
a small pipe.
With different angles of launching, we can pass multiple
signals through a single optical fibre simultaneously. This different signals
takes different parts and hence there is no messing up. They will reach two
different destinations without any problem.
Formation of Mirage
Mirage is nothing but the illusion of a object seen in
reverse that is inverted that when we see it from long distance during the summer seasons.This happens because of total internal reflection.
When a observer is standing at a distance and seeing an
object like a tree, he is seeing through the air. Direct light rays from the
object becomes little bit difficult when the object is far away. The light rays
from the object are reflected by the air layers that are there on the surface
of the earth towards the observer. Being the summer, the air layers will have
different temperatures. The air that is close to the surface of the earth is
higher than the upper layer.
As a result the lower layer is a rarer medium and
upper layer is a denser medium. As a light Ray is trying to pass from denser
medium to rarer medium, at a particular angle of incidence with experience a total
internal reflection. As a result the light Ray reflects back to the observer as
shown in the diagram. For the observer the light rays are extended through the
eye is the reverse direction to see the formation of the image of the object.
Thus the object appears like a inverted one for the observer and this phenomena
is called a mirage.
The duration of the sun visibility
When there is no atmosphere around the Sun we can see it both
in the morning and the evening straight from the origin. But there is a lot of
atmosphere around the Sun and it is exposed to different temperatures. It is
very clear that the air layer that is close to the surface of the earth will be
that lesser temperature than the upper layer. Hence the lower layers behave like
a denser medium and the upper layers behaves like a rarer medium. The phenomena
of the total internal reflection take place here also. Hence we can see the sun
even after the sun set was happened.
Total internal reflection in a prism
Basing on the definition of the total internal reflection
and the critical angle, we can calculate the value of the critical angle of a
glass prism as shown below. As the refractive index of the glass with respect
to Air is close to 3/2, the corresponding critical angle is close to 42°.
If the angle of incidence through one of the face of the
prism is more than 42°, then the light experience a total internal reflection as shown.
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