critical angle

An angle of incidence is the angle between a beam incident on a surface and the normal (line perpendicular to the surface at the point of incidence). The beam can be formed by any wave: optical, acoustical, microwave, X-ray etc. In Fig.1 the red line representing a ray makes an angle θ with the normal (dotted line). Another common usage is in aviation, where it refers to the angle between the wing's chord (aircraft) and the longitudinal axis of an aircraft (a fixed value). Fig.2 shows a side view of part of an ae ...

Including:

• Angle of incidence - Optics
• Angle of incidence - Aviation

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While it is true that the creation of an evanescent wave does not affect the conservation of energy under ordinary conditions, i.e. the evanescent wave transmits zero net energy, if a medium with a higher refractive index is placed less than several wavelengths distance from the boundary of the first medium, the strength of the evanescent wave will be large enough to effect a change in the field of the second material. Electrons driven by the field allow ...

See also:

Total internal reflection, Total internal reflection - Frustrated Total Internal Reflection

Read more here: » Total internal reflection: Encyclopedia II - Total internal reflection - Frustrated Total Internal Reflection

There are several ways to derive Snell's Law, and therefore the Angle of Refraction. The first way it was discovered was by an application of Fermat's principle which states that a light wave must take a path that is an extremum in time subject to the constraints present. Normally this is translated into "Light will always take the quickest path it can." From this principle, and using a bit of differential calculus, Snell’s Law can be derived thus leading to the Angle of Refraction. If one looks into the meaning of Fermat’s principle, ot ...

See also:

Angle of refraction, Angle of refraction - Derivation and Meaning of the Angle of Refraction, Angle of refraction - Results the Angle of Refraction

Read more here: » Angle of refraction: Encyclopedia II - Angle of refraction - Derivation and Meaning of the Angle of Refraction

A mirror provides the most common model for specular light reflection and consists of a glass sheet in front of a metallic coating where the reflection actually occurs. It is also possible for reflection to occur from the surface of transparent media, such as water or glass. In the diagram, a light ray PO strikes a vertical mirror at point O, and the reflected ray is OQ. By projecting an imaginary line through point O perpendicular to the mirror, known as the normal, we can measure the angle of in ...

See also:

Reflection physics, Reflection physics - Specular mirror-like reflection, Reflection physics - Other types of reflection, Reflection physics - Diffuse reflection, Reflection physics - Retroreflection, Reflection physics - Neutron reflection, Reflection physics - Quantum Interpretation

Read more here: » Reflection physics: Encyclopedia II - Reflection physics - Specular mirror-like reflection

In the diagram on the right, two media of refractive indices n1 (on the left) and n2 (on the right) meet at a surface or interface (vertical line). n2 > n1, and light has a slower phase velocity within the second medium. A light ray PO in the leftmost medium strikes the interface at the point O. From point O, we project a straight line at right angles to the line of the interface; this is known as the normal to the surface (horizontal line). The angle between the normal and the light ray PO is known as the See also:

Snell's law, Snell's law - Overview, Snell's law - Total internal reflection, Snell's law - Vector form, Snell's law - Derivation, Snell's law - History

Read more here: » Snell's law: Encyclopedia II - Snell's law - Overview

Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50 percent. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals such as macles are more likely to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to. The prevalence and choice of a particular fancy cut is also influenced by fash ...

See also:

Diamond cut, Diamond cut - Theory, Diamond cut - Choice of cut, Diamond cut - Round brilliant, Diamond cut - Facet count and names, Diamond cut - Proportions, Diamond cut - Fancy cuts, Diamond cut - Modified brilliants, Diamond cut - Step cuts, Diamond cut - Mixed cuts, Diamond cut - Rose cuts, Diamond cut - Cut grading, Diamond cut - History

Read more here: » Diamond cut: Encyclopedia II - Diamond cut - Fancy cuts

Reflection physics - Diffuse reflection. (main article diffuse reflection) Light bounces off in all directions due to the microscopic irregularities of the interface; this is an omnipresent phenomenon, applicable for all non-shiny objects that are not black. Reflection physics - Retroreflection. (main article retroreflection) Light bounces back in the direction from which it came due to the special structure of the surface. Reflection physics - Neutron reflection. Materials that reflect neutrons, for exam ...

See also:

Reflection physics, Reflection physics - Specular mirror-like reflection, Reflection physics - Other types of reflection, Reflection physics - Diffuse reflection, Reflection physics - Retroreflection, Reflection physics - Neutron reflection, Reflection physics - Quantum Interpretation

Read more here: » Reflection physics: Encyclopedia II - Reflection physics - Other types of reflection

All interactions between light photons and matter are described as a series of absorption and emission of photons. If one examines a single molecule at the surface of a material, an arriving photon will be absorbed and almost immediately reemitted. The ‘new’ photon may be emitted in any direction, thus causing diffuse reflection. The specular reflection (following Hero's equi-angular reflection law) is a quantum mechanical effect explained as the sum of the most likely paths the photons will have taken. Light-matter interaction is ...

See also:

Reflection physics, Reflection physics - Specular mirror-like reflection, Reflection physics - Other types of reflection, Reflection physics - Diffuse reflection, Reflection physics - Retroreflection, Reflection physics - Neutron reflection, Reflection physics - Quantum Interpretation

Read more here: » Reflection physics: Encyclopedia II - Reflection physics - Quantum Interpretation

The choice of diamond cut is often decided by the original shape of the rough stone, location of internal flaws or inclusions, the preservation of carat weight, and popularity of certain shapes amongst consumers. The cutter must consider each of these variables before proceeding. Most gem-quality diamond crystals are octahedrons in their rough state (see material properties of diamond). These crystals are usually cut into round brilliants because it is possible to cut two such stones out of one octahedron with minimal lo ...

See also:

Diamond cut, Diamond cut - Theory, Diamond cut - Choice of cut, Diamond cut - Round brilliant, Diamond cut - Facet count and names, Diamond cut - Proportions, Diamond cut - Fancy cuts, Diamond cut - Modified brilliants, Diamond cut - Step cuts, Diamond cut - Mixed cuts, Diamond cut - Rose cuts, Diamond cut - Cut grading, Diamond cut - History

Read more here: » Diamond cut: Encyclopedia II - Diamond cut - Choice of cut

In its rough state, a diamond is fairly unremarkable in appearance. Most gem diamonds are recovered from secondary or alluvial deposits, and such diamonds have dull, battered external surfaces often covered by a gummy, opaque skin—a comparison to "lumps of washing soda" is apt. The act of polishing a diamond and creating flat facets in symmetrical arrangement brings out the diamond's hidden beauty in dramatic fashion. When designing a diamond cut, two primary factors are considered. Foremost is the refractive index (RI) of diamond, ...

See also:

Diamond cut, Diamond cut - Theory, Diamond cut - Choice of cut, Diamond cut - Round brilliant, Diamond cut - Facet count and names, Diamond cut - Proportions, Diamond cut - Fancy cuts, Diamond cut - Modified brilliants, Diamond cut - Step cuts, Diamond cut - Mixed cuts, Diamond cut - Rose cuts, Diamond cut - Cut grading, Diamond cut - History

Read more here: » Diamond cut: Encyclopedia II - Diamond cut - Theory

Given a normalized ray vector v and a normalized plane normal vector p, one can work out the normalized reflected and refracted rays: (note that the actual angles θ1 and θ2 are not worked out) The cosines may be recycled and used in the Fresnel equations for working out the intensity of the resulting rays. During total internal reflection an evanescent wave is produced, which rapidly decays from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, ...

See also:

Snell's law, Snell's law - Overview, Snell's law - Total internal reflection, Snell's law - Vector form, Snell's law - Derivation, Snell's law - History

Read more here: » Snell's law: Encyclopedia II - Snell's law - Vector form

The history of diamond cuts can be traced to the late Middle Ages, before which time diamonds were enjoyed in their natural octahedral state—anhedral (poorly formed) diamonds simply were not used in jewellery. The first "improvements" on nature's design involved a simple polishing of the octahedral crystal faces to create even and unblemished facets, or to fashion the desired octahedral shape out of an otherwise unappealing piece of rough. This was called the point cut and dates from the mid 14th century; by 1375 there was a guild o ...

See also:

Diamond cut, Diamond cut - Theory, Diamond cut - Choice of cut, Diamond cut - Round brilliant, Diamond cut - Facet count and names, Diamond cut - Proportions, Diamond cut - Fancy cuts, Diamond cut - Modified brilliants, Diamond cut - Step cuts, Diamond cut - Mixed cuts, Diamond cut - Rose cuts, Diamond cut - Cut grading, Diamond cut - History

Read more here: » Diamond cut: Encyclopedia II - Diamond cut - History

When moving from a dense to a less dense medium (i.e. n1 > n2), it is easily verified that the above equation has no solution when θ1 exceeds a value known as the critical angle: When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes total internal reflection from the interface. ...

See also:

Snell's law, Snell's law - Overview, Snell's law - Total internal reflection, Snell's law - Vector form, Snell's law - Derivation, Snell's law - History

Read more here: » Snell's law: Encyclopedia II - Snell's law - Total internal reflection

The "Cut" of the "4-Cs" is the most difficult part for a consumer to judge when selecting a good diamond. This is because some certificates, such as those issued by the Gemological Institute of America, will not show the important measurements influencing cut (such as the pavilion angle and crown angle) and will not provide a subjective ranking of how good the cut was. The other 3-Cs can be ranked simply by the rating in each category. It requires a trained eye to judge the quality of a diamond cut, and the task is complicated by the fact that different standards are used in different countrie ...

See also:

Diamond cut, Diamond cut - Theory, Diamond cut - Choice of cut, Diamond cut - Round brilliant, Diamond cut - Facet count and names, Diamond cut - Proportions, Diamond cut - Fancy cuts, Diamond cut - Modified brilliants, Diamond cut - Step cuts, Diamond cut - Mixed cuts, Diamond cut - Rose cuts, Diamond cut - Cut grading, Diamond cut - History

Read more here: » Diamond cut: Encyclopedia II - Diamond cut - Cut grading

Developed ca. 1900, the round brilliant is the most popular cut given to diamond. It is usually the best choice in terms of saleability, insurability (due to its relatively "safe" shape), and desired optics. Diamond cut - Facet count and names. The modern round brilliant (Figure 1 and 2) consists of 58 facets (or 57 if the culet is excluded); 33 on the crown (the top half above the middle or girdle of the stone) and 25 on the pavilion (the lower half below the girdle). The girdl ...

See also:

Diamond cut, Diamond cut - Theory, Diamond cut - Choice of cut, Diamond cut - Round brilliant, Diamond cut - Facet count and names, Diamond cut - Proportions, Diamond cut - Fancy cuts, Diamond cut - Modified brilliants, Diamond cut - Step cuts, Diamond cut - Mixed cuts, Diamond cut - Rose cuts, Diamond cut - Cut grading, Diamond cut - History

Read more here: » Diamond cut: Encyclopedia II - Diamond cut - Round brilliant