Refraction is the bending of waves as they pass from one medium to another due to a change in speed. It applies to light, sound, and water waves and can cause objects to appear displaced. Refractive index indicates how fast waves will travel in a medium and increases with density. Refraction is used in lenses and prisms. Snell’s Law describes the phenomenon mathematically. Examples include a straw in water, mirages, and rainbows.
Refraction is the curvature of waves as they pass from one medium to another, due to a change in their speed. The phenomenon is most commonly associated with light, but can also apply to sound, or even water, waves. It occurs when a series of waves travels towards the new vehicle at an angle, so that one side experiences a change in speed before the other, causing it to turn towards the slower side in the same way that a moving vehicle will tend to turn if a side is slowed down more than the other. Refraction can cause objects to appear displaced and can amplify distant sounds. It has many uses in the context of light, such as lenses and prisms.
Refractive index
Every medium through which waves can move has a refractive index that indicates how fast they will travel. In the case of light, this is found by dividing its speed in a vacuum by its speed in that particular medium. It is a ratio between the speeds of the vehicles, so it is not measured in any unit. The refractive index generally increases with the density of the medium: it is one for vacuum and is greater than one for all known natural materials.
Air typically has a refractive index of about 1.00029, but this varies with temperature and pressure. For water the value is around 1.33 and for glass around 1.50 – 1.75, depending on the type. The diamond has a very high refractive index of 2.417, which produces the well-known sparkling effect.
Everyday examples
The most common example used when discussing refraction is a straw in water. When a straw is placed in a glass of water and viewed from the side, it looks broken or bent. This is due to the difference in the refractive indices of air and water. Since water is denser than air, the straw appears to bend as the light it reflects is slowed down by the density of the water. This phenomenon also causes submerged objects, such as fish, to appear closer to the surface than they actually are.
Because the refractive index of air varies with temperature and pressure, objects can appear displaced or distorted under certain conditions. The familiar illusion of water lying on a road on a hot day is one example: it is a refracted image of the sky caused by warming air near the road surface. Sometimes layers of air of different temperatures and pressures can make objects beyond the horizon visible – this is known as a mirage. Different layers of air can produce similar phenomena with sound. Under the right conditions, distant sounds can seem close because some of the sound waves, initially directed above the listener, can be bent downward, increasing the volume.
A more common example is a rainbow, where sunlight is refracted by raindrops. Sunlight consists of a mixture of different wavelengths, or colors, of light, with blue, for example, having a shorter wavelength than red. As this light passes through raindrops, the shorter wavelengths bend more than the longer ones, breaking the light up into its different colors.
it is used
The most common uses of refraction are in lenses and prisms. A lens is designed so that light entering it is focused by refraction towards a point, producing a magnified image of an object. The lenses can be used in binoculars and telescopes to obtain detailed images of distant objects, or in magnifiers and microscopes to view very small objects, such as microorganisms not visible to the naked eye. A prism can be used to split light into different colors in much the same way that water droplets create a rainbow, but giving a more accurate image that can be used to analyze the light source in detail.
Snell’s law
The phenomenon of refraction has been known since at least ancient Greek times, and a number of people throughout history have formulated laws to describe it, including Ibn Sahl of Baghdad, who drew up a very accurate description in 984, which he used to create lenses. Dutch astronomer Willebrord van Roijen Snell produced a mathematical law in 1621, which was later modified into the formula called “Snell’s Law” by René Descartes in 1637. It can be used to calculate the angle of refraction for passing light through two different means.
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