Technological Inventions of
Refraction
DONE BY: FOO KAI SIANG
3A311
Introduction to Refraction
 Refraction is the bending of a wave when it enters a
medium where it's speed is different.
 The refraction of light when it passes from a fast
medium to a slow medium bends the light ray toward
the normal to the boundary between the two media.
 The amount of bending depends on the indices of
refraction of the two media and is described
quantitatively by Snell's Law.
Snell’s Law
 Snell's law gives the relationship between angles of
incidence and refraction for a wave impinging on an
interface between two media with different indices of
refraction.
 The law follows from the boundary condition that a
wave be continuous across a boundary, which requires
that the phase of the wave be constant on any given
plane.
 This is the formula for Snell’s Law:
Inventions based on Refraction
 Cerenkov Radiation in a Nuclear reactor
 Microscopes
 Prism
 Spectacles
 Gravitational Lensing
Cerenkov Radiation in a Nuclear reactor
 When charged particles such as electrons travel
through a dielectric medium with a speed greater than
the phase velocity of the light in the medium,
electromagnetic radiation is emitted that falls into a
cone fanning out in the forward direction.
 This phenomenon is called Čerenkov radiation, named
after the Russian scientist who first characterized it
rigorously and was awarded the Nobel Prize in Physics
in 1958.
Cerenkov Radiation in a Nuclear reactor
 The angle of the Čerenkov emission cone is related in a
simple way to the particle velocity.
 This unique feature enables a wide range of
applications, from the measurement of fast particles in
high-energy physics, the characterization of fission rate
in nuclear reactors, to the detection of labeled
biomolecules.
Cerenkov Radiation in a Nuclear reactor
 The direction of the cone of Čerenkov radiation can
also be reversed in artificially engineered composite
media, namely, metamaterials
 From one point of view, this experiment could be
considered as a special case of negative refraction, in
which the light is negatively refracted from a low
positive index medium to a high negative index
medium at a grazing incident angle.
Microscopes
 The ability of the microscope to both magnify and
resolve (or allow small structures to be seen) firstly
depends on the refraction or bending of light.
 The amount of refraction that occurs depends on the
difference in Refractive Index of the two media or
materials and is described by Snell's law:
η1 sin θ1 = η2 sin θ2
Microscopes
 Unfortunately, an image made by a single lens suffers from
a number of optical defects. These can include:
chromatic aberration, spherical aberration, astigmatism
and curvature of field
 In order to combat these defects and produce sharp images,
microscope objectives and eyepieces are far more complex
and are comprised of multiple lenses made of glass with
differing refractive indices.
 Microscope objectives come in several grades of correction.
Microscopes
 While the power of a lens indicates the magnification
it gives, the numerical aperture gives a relative
indication of its resolving power, which is more
important than magnification.
 Bigger is not always better, especially when it comes
to magnification, unless it is accompanied by
increased resolution of fine detail.
Microscopes
 The final magnification will be the product
of the objective magnification, the eyepice
magnification and perhaps other factors
such as the tube factor, the nose piece factor
and the camera factor.
Prism
 In optics, a prism is a transparent optical element with
flat, polished surfaces that refract light. The exact
angles between the surfaces depend on the application.
 The traditional geometrical shape is that of a triangular
prism with a triangular base and rectangular sides, and
in colloquial use "prism" usually refers to this type.
Some types of optical prism are not in fact in the shape
of geometric prisms.
Prism
 Prisms are typically made out of glass, but can be made
from any material that is transparent to
the wavelengths for which they are designed.
 A prism can be used to break light up into its
constituent spectral colors (the colors of the rainbow).
Prisms can also be used to reflect light, or to split light
into components with different polarizations.
Prism
 In Isaac Newton's time, it was believed that white light
was colorless, and that the prism itself produced the
color. Newton's experiments convinced him that all the
colors already existed in the light in a heterogeneous
fashion, and that "corpuscles" (particles) of light were
fanned out because particles with different colors
traveled with different speeds through the prism.
Prism
 It was only later that Young and Fresnel combined
Newton's particle theory with Huygen's wave theory to
show that color is the visible manifestation of light's
wavelength.
 Newton arrived at his conclusion by passing the red color
from one prism through a second prism and found the color
unchanged.
 From this, he concluded that the colors must already be
present in the incoming light — thus, the prism did not
create colors, but merely separated colors that are already
there.
Spectacles
 Many people around the world cannot see things clearly
without the help of spectacles. They suffer from myopia
(nearsightedness) or hyperopia (farsightedness).
 Spectacles are frames with lenses worn in front of the
eyes for vision correction and also eye protection.
 Spectacles work by adjusting the focal length of a
persons eyes if they are not naturally correct.
 The eyeball has a particular shape that acts as a lens so
that you can focus on objects.In the event of the eyes
getting weak they compensate for this
Spectacles
 Corrective lenses modify the focal length of the eye to
alleviate the effects of myopia and hyperopia or
astigmatism.
 As people age, the eye's crystalline lens loses
elasticity, resulting in presbyopia, which limits their
ability to change focus.
The power of a lens is generally measured in
diopters.
Spectacles
 Over-the-counter reading glasses are typically rated
at +1.00 to +4.00 diopters.
 Glasses correcting for myopia will have negative
diopter strengths. Lenses made to conform to the
prescription of an ophthalmologist or optometrist
are called prescription lenses and are used to make
prescription glasses.
Gravitational Lensing
 A gravitational lens is formed when the light from
a very distant, bright source is "bent" around a
massive object between the source object and the
observer.
 The process is known as gravitational lensing,
 One of Albert Einstien’s prediction on general theory
of relativity.
Gravitational Lensing
 This is a diagram which illustrates the bending of the
light in gravitational lensing.
Gravitational Lensing
 There are three classes of gravitational lensing:
 1. Strong lensing: where there are easily visible
distortions such as the formation of Einstein rings, arcs,
and multiple images.
 2. Weak lensing: where the distortions of background
sources are much smaller and can only be detected by
analyzing large numbers of sources to find coherent
distortions of only a few percent.
 3. Microlensing: where no distortion in shape can be seen
but the amount of light received from a background
object changes in time.
Gravitational Lensing
 In general relativity, the presence of matter (energy density)
can curve spacetime, and the path of a light ray will be
deflected as a result.
 This, in many cases can be described in analogy to the
deflection of light by (e.g. glass) lenses in optics. Many useful
results for cosmology have come out of using this property of
matter and light.
 In this case, refraction of light was carried out as the light was
bent around matter
Gravitational Lensing
 Scientists thought that Einstein was crazy when he told them
that light would bend around a galaxy.
 However, finally, he was proven right as research shown in a
galaxy far away proven and showed that light can and will
bend if it meets with great amount of matter e.g. dark matter.
 What a brave and far-sighted man Einstein has proven to be!
Conclusion
 Refraction has proven to be useful in more areas
then 1,
 We have seen refraction work its wonders in:
1. Everyday Lives
2. Astronomy
3. Studying of very small objects
4. Nuclear Technology
Conclusion
 I believe that with the ability to understand and
make good use of the bending of light, we can create
and break technological boundaries.
 I believe that we are on the verge of the next big
break in terms of our knowledge and technology in
physics if we can all have deeper and more in depth
knowledge about refractions
 After all, we have already made use of it for so many
inventions, haven’t we?
Reflections
 I felt that it was a fascinating and eye-opening
experience to do such a presentation
 I believe that by doing this research, I have enhanced
my knowledge on a enriching and important topic
for many years to come.
 It is my pleasure to do another presentation like this
again.
Bibiography
 http://www.physicsforums.com/showthread.php?t=
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316262
http://scienceworld.wolfram.com/physics/SnellsLa
w.html
http://physics.aps.org/articles/v2/91
http://web.uvic.ca/ail/techniques/scope_basics.htm
l
http://imagine.gsfc.nasa.gov/docs/features/news/gr
av_lens.html
http://astro.berkeley.edu/~jcohn/lens.html
Thank You