ϵ displaystyle epsilon ) and mu( μ displaystyle mu ) represent the dielectric constant and the magnetic moment of the different media:[1] sin θ 1 sin θ 2 = v 1 v 2 = n 2 n 1 = ( ϵ 2 μ 2 ϵ 1 μ 1 ) displaystyle frac sin theta _ 1 sin theta _ 2 = frac v_ 1 v_ 2 = frac n_ 2 n_ 1 = sqrt left( frac epsilon _ 2 mu _ 2 epsilon _ 1 mu _ 1 right) In general, the incident wave is partially refracted and partially reflected (internal refraction); the details of this behavior are described by the Fresnel equations. Contents 1 Explanation 2 Clinical significance 3 Acoustics 4 Gallery 5 See also 6 References 7 External links Explanation[edit]
In optics, refraction is a phenomenon that often occurs when waves
travel from a medium with a given refractive index to a medium with
another at an oblique angle. At the boundary between the media, the
wave's phase velocity is altered, usually causing a change in
direction. Its wavelength increases or decreases, but its frequency
remains constant.[citation needed] For example, a light ray will
refract as it enters and leaves glass, as there is a change in
refractive index. A ray traveling along the normal (perpendicular to
the boundary) will suffer change in speed, but not direction.
An object (in this case 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. (More accurately, for any angle of view, Y should be vertically above X, and the pencil should appear shorter, not longer as shown.)
Diagram of refraction of water waves The diagram on the right shows an example of refraction in water
waves. Ripples travel from the left and pass over a shallower region
inclined at an angle to the wavefront. The waves travel slower in the
more shallow water, so the wavelength decreases and the wave bends at
the boundary. The dotted line represents the normal to the boundary.
The dashed line represents the original direction of the waves. This
phenomenon explains why waves on a shoreline tend to strike the shore
close to a perpendicular angle. As the waves travel from deep water
into shallower water near the shore, they are refracted from their
original direction of travel to an angle more normal to the
shoreline.[3]
Play media 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. An analogy that is often put forward to explain the refraction of
light is as follows: "Imagine a marching band as it marches at an
oblique angle from a pavement (a fast medium) into mud (a slower
medium). The marchers on the side that runs into the mud first will
slow down first. This causes the whole band to pivot slightly toward
the normal (make a smaller angle from the normal)."
Why refraction occurs when light travels from a medium with a given
refractive index to a medium with another, can be explained by the
path integral formulation of quantum mechanics (the complete method
was developed in 1948 by Richard Feynman). Feynman humorously
explained it himself in the recording "QED: Fits of Reflection and
Transmission - Quantum Behaviour -
Clinical significance[edit] 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.[5] Acoustics[edit] In underwater acoustics, refraction is the bending or curving of a sound ray that results when the ray passes through a sound speed gradient from a region of one sound speed to a region of a different speed. The amount of ray bending is dependent on the amount of difference between sound speeds, that is, the variation in temperature, salinity, and pressure of the water.[6] Similar acoustics effects are also found in the Earth's atmosphere. The phenomenon of refraction of sound in the atmosphere has been known for centuries;[7] however, 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.[8] Gallery[edit]
The straw appears to be broken because of the difference between the angle at which light from it strikes the vertical edge of the glass versus the horizontal surface of the water. Photograph of refraction of waves in a ripple tank. .
Double aorta artifact in sonography due to difference in velocity of sound in muscle and fat. See also[edit]
References[edit] ^ Born and Wolf (1959). Principles of Optics. New York, NY: Pergamon
Press INC. p. 37.
^ Dill, Lawrence M. (1977). "
External links[edit] Wikimedia Commons has media related to Refraction. Java illustration of refraction Java simulation of refraction through a prism Reflections and Refractions in Ray Tracing, a simple but thorough discussion of the mathematics behind refraction and reflection. Flash refraction simulation- includes source, Explains refraction and Snell's Law. Animations demonstrating optical refraction by QED Authority control LCCN: sh85112257 GND: 4146523-4 SUDOC: 027859770 BNF: cb119811319 (d |