DONE BY: FOO KAI SIANG3A311

Technological Inventions of Refraction

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 reactorMicroscopesPrismSpectaclesGravitational 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.

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. 

Microscopes

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 Lives2. Astronomy3. Studying of very small objects4. 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=316262

http://scienceworld.wolfram.com/physics/SnellsLaw.html

http://physics.aps.org/articles/v2/91http://web.uvic.ca/ail/techniques/scope_basics

.htmlhttp://imagine.gsfc.nasa.gov/docs/features/ne

ws/grav_lens.htmlhttp://astro.berkeley.edu/~jcohn/lens.html

Thank You