Refraction

In physics, refraction is the redirection of a wave as it passes from one medium to another.

For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence

Optical prisms and lenses use refraction to redirect light, as does the human eye.

This is called dispersion and causes prisms and rainbows to divide white light into its constituent spectral colors.

[4] A correct explanation of refraction involves two separate parts, both a result of the wave nature of light.

This slowing applies to any medium such as air, water, or glass, and is responsible for phenomena such as refraction.

(The material's protons also oscillate but as they are around 2000 times more massive, their movement and therefore their effect, is far smaller).

A moving electrical charge emits electromagnetic waves of its own.

When the light leaves the material, this interaction with electrons no longer happens, and therefore the wave packet rate (and therefore its speed) return to normal.

This is why a wave will bend away from the surface or toward the normal when going into a slower material.

The phenomenon of refraction can in a more fundamental way be derived from the 2 or 3-dimensional wave equation.

Refraction is also responsible for rainbows and for the splitting of white light into a rainbow-spectrum as it passes through a glass prism.

When a beam of white light passes from air into a material having an index of refraction that varies with frequency (and wavelength), a phenomenon known as dispersion occurs, in which different coloured components of the white light are refracted at different angles, i.e., they bend by different amounts at the interface, so that they become separated.

This is due to the bending of light rays as they move from the water to the air.

This is an important consideration for spearfishing from the surface because it will make the target fish appear to be in a different place, and the fisher must aim lower to catch the fish.

[8] For small angles of incidence (measured from the normal, when sin θ is approximately the same as tan θ), the ratio of apparent to real depth is the ratio of the refractive indexes of air to that of water.

But, as the angle of incidence approaches 90°, the apparent depth approaches zero, albeit reflection increases, which limits observation at high angles of incidence.

Since the pressure is lower at higher altitudes, the refractive index is also lower, causing light rays to refract towards the earth surface when traveling long distances through the atmosphere.

Temperature variations in the air can also cause refraction of light.

This effect is also visible from normal variations in air temperature during a sunny day when using high magnification telephoto lenses and is often limiting the image quality in these cases.

[9] In a similar way, atmospheric turbulence gives rapidly varying distortions in the images of astronomical telescopes limiting the resolution of terrestrial telescopes not using adaptive optics or other techniques for overcoming these atmospheric distortions.

Air temperature variations close to the surface can give rise to other optical phenomena, such as mirages and Fata Morgana.

Most commonly, air heated by a hot road on a sunny day deflects light approaching at a shallow angle towards a viewer.

In medicine, particularly optometry, ophthalmology and orthoptics, refraction (also known as refractometry) is a clinical test in which a phoropter may be used by the appropriate eye care professional to determine the eye's refractive error and the best corrective lenses to be prescribed.

A series of test lenses in graded optical powers or focal lengths are presented to determine which provides the sharpest, clearest vision.

[10] Refractive surgery is a medical procedure to treat common vision disorders.

This can be used to demonstrate refraction in ripple tanks and also explains why waves on a shoreline tend to strike the shore close to a perpendicular angle.

[12] Similar acoustics effects are also found in the Earth's atmosphere.

[13] Beginning in the early 1970s, widespread analysis of this effect came into vogue through the designing of urban highways and noise barriers to address the meteorological effects of bending of sound rays in the lower atmosphere.

A ray of light being refracted in a plastic block
Refraction of light at the interface between two media of different refractive indices, with n 2 > n 1 . Since the phase velocity is lower in the second medium ( v 2 < v 1 ), the angle of refraction θ 2 is less than the angle of incidence θ 1 ; that is, the ray in the higher-index medium is closer to the normal.
A pen partially submerged in a bowl of water appears bent due to refraction at the water surface.
When a wave moves into a slower medium the wavefronts get compressed. For the wavefronts to stay connected at the boundary the wave must change direction.
Rainbows are formed by dispersion of light, in which the refraction angle depends on the light's frequency.
A pencil part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y.
An image of the Golden Gate Bridge is refracted and bent by many differing three-dimensional drops of water.
Comparison of inferior and superior mirages due to differing air refractive indices, n
The sun appears slightly flattened when close to the horizon due to refraction in the atmosphere.
Heat haze in the engine exhaust above a diesel locomotive
Mirage over a hot road
Water waves are almost parallel to the beach when they hit it because they gradually refract towards land as the water gets shallower.
2D simulation: refraction of a quantum particle. The black half of the background is zero potential, the gray half is a higher potential. White blur represents the probability distribution of finding a particle in a given place if measured.