Transcript Refraction and its uses

Refraction and its Uses
Done by: Andrew Ong
Content
Uses of refraction in
• Optic fibres
• Telescopes
• Glasses
• Cameras
• Magnifying glass
Plus:
1)Water-filled spheres,
known an lacemakers'
condensors
2) Schlieren Photography
3) Mirages
Refraction
• Refraction is defined as the bending of a light
wave when it passes from one medium to
another at the surface separating the two
media. It basically occurs due to the speed of
light being different in different media of
different densities.
Refraction
• Refraction of light waves is governed by the
two Laws of Refraction:
• The incident ray, refracted ray and the normal
at the point of incidence lie in the same plane.
• The sine of the angle of incidence bears a
constant ratio with the sine of the angle of
refraction for a given pair of media. This is also
known as Snell’s Law.
n1sinθ1 = n2sinθ2
Refraction
r <i
Ray of light bends towards
the normal when it enters a
denser medium at an angle
r >i
Ray of light bends away from
the normal when it enters a
less dense medium at an
angle
Optic Fibres
• The light in a fiber-optic cable travels through
the core by constantly bouncing from the
cladding using a principle called total internal
reflection. Because the cladding does not
absorb any light from the core, the light wave
can travel great distances.
Optic Fibres
• The core is the inner part of the fiber, which
guides light. The cladding surrounds the core
completely.
• The refractive index of the core is higher than
that of the cladding, so light in the core that
strikes the boundary with the cladding at an
angle shallower than critical angle will be
reflected back into the core by total internal
reflection.
Total Internal Reflection
• The core is optically more dense than the
cladding. The light ray will undergo total
internal reflection as it strikes the interface
between the core and cladding as the incident
ray has exceeded the critical angle.
Total Internal Reflection – Critical Angle
• Diagram on how refraction/ total internal
reflection works
Medium of lower refractive index
Angle of refraction = 90º
Refracted beam
Critical
angle ic
normal
Medium of
higher refractive index
Partially reflected beam
Total Internal Reflection
Air (n=1.0)
Water (n=1.3)
Snell’s law:
qc
n2 sin 1

n1 sin  2
Advantages of Fiber Optics
• Why are fiber-optic systems revolutionizing telecommunications?
Compared to conventional metal wire (copper wire), optical fibers are:
• Less expensive - Several miles of optical cable can be made cheaper than
equivalent lengths of copper wire. This saves your provider (cable TV,
Internet) and you money.
• Thinner - Optical fibers can be drawn to smaller diameters than copper
wire.
• Higher carrying capacity - Because optical fibers are thinner than copper
wires, more fibers can be bundled into a given-diameter cable than copper
wires. This allows more phone lines to go over the same cable or more
channels to come through the cable into your cable TV box.
• Less signal degradation - The loss of signal in optical fiber is less than in
copper wire.
• Light signals - Unlike electrical signals in copper wires, light signals from
one fiber do not interfere with those of other fibers in the same cable.
This means clearer phone conversations or TV reception.
Advantages of Fiber Optics
• Low power - Because signals in optical fibers degrade less, lowerpower transmitters can be used instead of the high-voltage
electrical transmitters needed for copper wires. Again, this saves
your provider and you money.
• Digital signals - Optical fibers are ideally suited for carrying digital
information, which is especially useful in computer networks.
• Non-flammable - Because no electricity is passed through optical
fibers, there is no fire hazard.
• Lightweight - An optical cable weighs less than a comparable
copper wire cable. Fiber-optic cables take up less space in the
ground.
• Flexible - Because fiber optics are so flexible and can transmit and
receive light, they are used in many flexible digital cameras for the
following purposes:
Telescopes(or Refractors)
• Commonly known as refractors, telescopes of this
kind are used to examine the visible-light region
of the electromagnetic spectrum. Typical uses
include viewing the Moon, other objects of the
solar system such as Jupiter and Mars, and
double stars. Usually used to view objects at a
great distance away from the viewer.
• The name refractor is derived from the term
refraction, which is the bending of light when it
passes from one medium to another of different
density.
Telescopes(or Refractors)
• The focus is the point, or plane, at
which light rays from infinity converge
after passing through a lens and
traveling a distance of one focal
length. In a refractor, the first lens
through which light from a celestial
object passes is called the objective
lens. It should be noted that the light
will be inverted at the focal plane.
• A second lens, referred to as the
eyepiece lens(used to invert the image
formed from the first lens), is placed
behind the focal plane and enables the
observer to view the magnified,
upright image.
Telescopes(or Refractors)
• Hence, in a telescope, light from a very
faraway object(which gives out parallel rays of
light), is refracted and converged to a smaller
Image seen will be
focus at the eye.
upright, magnified and
clear
• This results in a clear, upright
and magnified image forming at the eye.
Glasses(Eye refraction disorders)
• Myopia Those with myopia see near
objects clearly but far away objects
appear blurred. With myopia, the eyeball
is too long, or the cornea is too steep, so
images are focused before the retina,
rather than on the retina at the back of
the eye.
• Hyperopia The opposite defect of
myopia is hyperopia or "farsightedness"
or "long-sightedness"—this is where the
cornea is too flat or the eye is too small.
Glasses
• Corrective lenses are used to correct refractive
errors of the eye by modifying the focal length
of the lens in order to solve the effects of
conditions such as:
1)nearsightedness (myopia),
2)farsightedness (hyperopia)
Diagrams of Myopia, Hyperopia
• Myopia
• Hyperopia
Vision(Eye)
• The process of vision begins when light rays that reflect off
objects and travel through the eye's optical system are
refracted and focused into a point of sharp focus.
• For good vision, this focus point must be on the retina. The
retina is the tissue that lines the inside of the back of the
eye, where light-sensitive cells capture images in much the
same way that film in a camera does when exposed to light.
These images then are transmitted through the eye's optic
nerve to the brain for interpretation.
• The eye's pupil widens or constricts to control the amount
of light that reaches the retina. In dark conditions, the pupil
widens. In bright conditions, the pupil constricts.
Vision(Eye)
• When light travels through water or a lens, for
example, its path is bent or refracted. Eye structures
have refractive properties similar to water or lenses
and can bend light rays into a precise point of focus(at
the retina) essential for sharp vision.
• Most refraction in the eye occurs when light rays travel
through the curved, clear front surface of the eye
(cornea). The eye's natural (crystalline) lens also bends
light rays. Even the eye's tear film and internal fluids
(aqueous humor and vitreous) have refractive abilities.
Camera
• A camera's aperture (called the diaphragm) is
used to adjust the amount of light needed to
expose film in just the right way.
• The optical component of the camera is the lens.
At its simplest, a lens is just a curved piece of
glass or plastic. Its job is to take the beams of
light bouncing off of an object and redirect them
so they come together to form a real image -- an
image that looks just like the scene in front of the
lens.
Cameras
• Just like the eye, the camera lens has a different
optical density than the surrounding
environment. Hence, parallel light beams from a
faraway object would converge at a single point,
forming a diminished and inverted image.
• Hence, at the eyepiece, there is another piece of
lens which causes the image to appear upright
and magnified, which the human eyes picture.
Magnifying Glass
• A magnifying glass is a convex lens which is used
to produce a magnified image of an object.
• A magnifying glass works by creating a magnified
virtual image of an object behind the lens. The
distance between the lens and the object must
be shorter than the focal length of the lens for
this to occur. Otherwise, the image appears
smaller and inverted, and can be used to project
images onto surfaces.
Magnifying Glass
• Diagram of Magnifying Glass
Lacemakers’ condensors
• The refraction of light can be used for various
purposes. Water-filled spheres, known an
lacemakers' condensors, were used in the early
nineteenth century by lacemakers to help them
see their work.
• Light passing through these condensors was bent
and refracted in such a way, so that the rays meet
and converge at a small and concentrated point
and light up only a small area of the cloth to
enable the lacemaker to focus on it.
Schlieren Photography(Apparent Depth)
• Schlieren Photography, which uses the fact that
air at different temperatures bends light by
different amounts. The refractive index of a
particular substance which occurs in a huge
quantity such as a water reservoir can also be
used to measure its real depth by measuring the
apparent depth.
• Since light coming from a denser medium such as
glass or water is bent away from the normal, the
depth at which an object inside that medium
appears to be less than its real depth.
Schlieren Photography(Apparent Depth)
• An object seen in the water will usually appear
to be at a different depth than it actually is, this
is due to the refraction of light rays as they
travel from the water into the air.
Apparent
depth
Schlieren Photography(Apparent Depth)
Mirage
• When light travels from a rarer medium to a denser one, it bends
towards the normal. When it travels from a denser medium to a
rarer one, it bends away from the normal. This bending of light has
many implications, one of which is quite prominent in nature mirage.
• A mirage occurs in very hot conditions, when a layer of warm air,
next to the ground is trapped by the relatively cooler air above.
Light is successively bent by these different layers of different
densities towards the horizontal line of vision and eventually is
made to travel upwards by total internal reflection at one of these
layers.
• When these light rays reach the human eye, the human brain
perceives them as coming from the image of the object, beneath it,
thus giving the wrong impression of a pool of water at some
distance. This phenomenon is most prominent on long roads on
very hot days and in hot deserts.
Mirage
• Another type of mirage, called looming,
occurs in extemely cold conditions, when a
layer of relatively warm air, lies over another
of cool air. The light rays travelling from the
cold to the warm layer are bent away from the
normal, and finally reflected downwards, to
give an impression of an image looming above
the real object.
References
• http://csep10.phys.utk.edu/astr162/lect/light/refracting.ht
ml
• http://www.google.com.sg/images?hl=en&q=refraction%2
0in%20the%20eye&um=1&ie=UTF8&source=og&sa=N&tab=wi
• http://en.wikipedia.org/wiki/Myopia
• http://www.wisegeek.com/what-is-refraction.htm
• http://homepage.usask.ca/~dln136/refraction/pages/third
_resources.html
• http://communication.howstuffworks.com/fiber-opticcommunications/fiber-optic2.htm
• http://www.google.com.sg/images?q=refraction+in+magnif
ying+glass&um=1&hl=en&tbs=isch:1&sa=N&start=20&nds
p=20