When electromagnetic radiation in the form of visible light travels from one substance or medium to another, the light waves may be exposed to a phenomenon called refraction, which manifest itself by bending or changing the direction of the light. Refraction occurs when light passes from one mediun to another only if there is a difference in the refractive index between the two materials. Refraction effects are responsible for a number of well-known phenomena, such as the apparent bending of an object partially immersed in water and the mirage observed in a dry, sandy desert. The refraction of visible light is also an important feature of lenses, allowing them to focus a beam of light on a single point.
Introduction to the refraction light – When light passes from one substance to another, it moves in a straight line without changing direction if it crosses the boundary between the two substances frontally (vertically or at an angle of incidence of 90 degrees). However, when light hits the boundary at a different angle, it is bent or refracted, with the degree of refraction increasing as the beam is progressively tilted at a greater angle to the boundary. For example, a beam of light that hits the water perpendicularly is not refracted, but if the beam enters the water at a slight angle, it is refracted to a very small degree. If the angle of the beam is increased even further, the light will be refracted as the angle of entry increases. Early scientists discovered that the ratio between the angle at which light crosses the media interface and the angle produced after refraction is a very precise property of the material that produces the refraction effect.
Friedrich Johann Karl Becke (1855 – 1931) – Friedrich Johann Karl Becke was an Austrian geologist, mineralogist and petrologist at the University of Prague who developed a method of determining the relationsship between light refraction and refractive index differences on microscopic samples. The phenomenon, now known as Becke line formation, was named after him.
Augustin-Jean Fresnel (1788-1827) – Augustin-Jean Fresnel, was a French physicist of the 19th century, best knwon for the invention of unique compound lenses to produce parallel light rays, which are still widely used in lighthouses. In the field of optics, Fresnel derived formulas to explain reflection, diffraction, interference, refraction, double refraction and polarization of light reflected by a transparent substance.
Willebrord Snell (1580 – 1626) – Willbrord Snell was a Dutch mathematician from the early seventeenth century who became for his discovery that transparent materials have different refractive indices depending on their composition. Snell discovered that a light beam would bend when it entered a glass block and that the angle of bending depended on the angle of incidence of the light beam. Light entering the glass in a straight lines does not bend, but is bent at an angle proportional to the angle of inclination. In 1621 Snell found a characteristic relationship between the angle of incidence and the angle of refraction. Snell`s law shows that every substance has a certain bending ratio – the “refractive index”, The larger the angle of refraction, the higher the refractive index for a substance.
Interactive JavaScript-Tutorials.
Light refraction – Light refraction occurs when light passes from one medium to another only when there is a difference in refractive index between the two materials. Refraction effects are responsible for a number of well-known phenomena, such as the apparent bending of an object partially immersed in water and the mirage observed in a dry, sandy desert. The refraction of visible light is also an important feature of lenses, allowing them to focus a light beam on a single point. This interactive tutorial examines how changes in the angle of incidence and the refractive index difference between two different media influence the angle of refraction of light at the interface.
Observing Objects in Water – An object seen in water usually appears at a different depth than it actually is due to the refraction of light rays entering the air from the water. This tutorial examines how fish observed from the shore of a pond or lale appear to be closer to the surface than they really are.
Refraction through an equilateral prism – Visible where light passing through an equilateral prism experiences a phenomenon known as dispersion, which manifests itself through the wavelenght-dependent refraction of light waves. This interactive tutorial explores how the angle of incidence of the white light entering the prism affects the degree of dispersion and the angles of light existing the prism.
Critical Angle of Refraction – An important concept in optical microscopy is the critical angle of reflection, which is a necessary factor in deciding whether to use dry or oil immersion objectives to view a sample at high magnification. When passing through a medium with a higher refractive index into a medium with a lower refractive index, the path of the light waves is determined by the angle of incidence in relation to the boundary between the two media. This interactive tutorial exemines the transition from refraction to total internal reflection, as the angle of the incidence wave is increased while the refractive index remains constant.
Beam Steering by Wedge Prisms – Beam Steering with flat surfaces positioned at small angles to each other are called optical wedges and deflect light by refraction instead of reflection. Although wedges are prismatic in nature, they can be manipulated to act as beam splitters or beam steerers. This interactive tutorial explores how two wedge prisms work together to deflect an incoming beam of light.
Refraction of monochromatic light – Refraction occurs as light passes from one medium to another, only if there is a difference in refractive index between the two materials. Refraction effects are responsible for a number of well-known phenomena, such as the apparent bending of an object partially immersed in water and the mirage observed in a dry, sandy desert. The refraction of visible light is also an important feature of lenses, allowing you to focus a beam of light on a single point. This interactive tutorial examines how changes in the angle of incidence and refractive index of monochromatic light at the interface.
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