Reflection (physics)

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Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.wikipedia
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Mirror

mirrorslooking glassreflector
Mirrors exhibit specular reflection.
A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection.

Specular reflection

specularreflectionlaw of reflection
The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected. Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface.
Specular reflection, also known as regular reflection, is the mirror-like reflection of waves, such as light, from a surface.

Echo

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In acoustics, reflection causes echoes and is used in sonar.
In audio signal processing and acoustics, echo is a reflection of sound that arrives at the listener with a delay after the direct sound.

Diffuse reflection

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Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface.
Diffuse reflection is the reflection of light or other waves or particles from a surface such that a ray incident on the surface is scattered at many angles rather than at just one angle as in the case of specular reflection.

Acoustics

acousticacousticianacoustical
In acoustics, reflection causes echoes and is used in sonar.
This interaction can be described as either a diffraction, interference or a reflection or a mix of the three.

Glass

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Reflection also occurs at the surface of transparent media, such as water or glass.
Glass will transmit, reflect and refract light; these qualities can be enhanced by cutting and polishing to make optical lenses, prisms, fine glassware, and optical fibers for high speed data transmission by light.

Total internal reflection

critical angleinternal reflectiontotally internally reflected
Total internal reflection of light from a denser medium occurs if the angle of incidence is greater than the critical angle.
Technically, TIR is the total reflection of a wave incident at a sufficiently oblique angle on the interface between two media, of which the second ("external") medium is transparent to such waves but has a higher wave velocity than the first ("internal") medium.

Fresnel equations

Fresnel reflectionFresnelFresnel coefficients
Solving Maxwell's equations for a light ray striking a boundary allows the derivation of the Fresnel equations, which can be used to predict how much of the light is reflected, and how much is refracted in a given situation.
When light strikes the interface between a medium with refractive index n 1 and a second medium with refractive index n 2, both reflection and refraction of the light may occur.

Sonar

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In acoustics, reflection causes echoes and is used in sonar.
Active sonar creates a pulse of sound, often called a "ping", and then listens for reflections (echo) of the pulse.

Radar

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Reflection of VHF and higher frequencies is important for radio transmission and for radar.
When these come into contact with an object they are usually reflected or scattered in many directions.

Thin-film optics

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This is an important principle in the field of thin-film optics.
These effects alter the way the optic reflects and transmits light.

Huygens–Fresnel principle

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All these waves add up to give specular reflection and refraction, according to the Huygens–Fresnel principle.
The Huygens–Fresnel principle (named after Dutch physicist Christiaan Huygens and French physicist Augustin-Jean Fresnel) is a method of analysis applied to problems of wave propagation both in the far-field limit and in near-field diffraction and also reflection.

Light

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Common examples include the reflection of light, sound and water waves.
Newton's theory could be used to predict the reflection of light, but could only explain refraction by incorrectly assuming that light accelerated upon entering a denser medium because the gravitational pull was greater.

Refractive index

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In fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive index.
Apart from the transmitted light there is also a reflected part.

Tapetum lucidum

eyeshinetapetumreflective eyes
Some animals' retinas act as retroreflectors (see tapetum lucidum for more detail), as this effectively improves the animals' night vision.
It reflects visible light back through the retina, increasing the light available to the photoreceptors (although slightly blurring the image).

Transparency and translucency

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Reflection also occurs at the surface of transparent media, such as water or glass.
As a result of these electrons, most of the incoming light in metals is reflected back, which is why we see a shiny metal surface.

Optical aberration

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A conjugate reflector can be used to remove aberrations from a beam by reflecting it and then passing the reflection through the aberrating optics a second time.
The articles on reflection, refraction and caustics discuss the general features of reflected and refracted rays.

Acoustic space

acoustic environments
Sound reflection can affect the acoustic space.

X-ray

X-raysX raysoft X-ray
Even hard X-rays and gamma rays can be reflected at shallow angles with special "grazing" mirrors.

Reflection seismology

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Shallower reflections are used in reflection seismology to study the Earth's crust generally, and in particular to prospect for petroleum and natural gas deposits.
Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves.

Anti-reflective coating

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An antireflective or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses and other optical elements to reduce reflection.

Sound

audiosound wavesound waves
Common examples include the reflection of light, sound and water waves.
During propagation, waves can be reflected, refracted, or attenuated by the medium.

Refraction

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In the most general case, a certain fraction of the light is reflected from the interface, and the remainder is refracted.

Snell's law

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Total internal reflection of light from a denser medium occurs if the angle of incidence is greater than the critical angle.

Project Echo

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Each of the two American spacecraft, launched in 1960 and 1964, was a metalized balloon satellite acting as a passive reflector of microwave signals.