Yes! Every wavelength of light is affected to a different degree by the refractive index of a transparent medium and as a result, changes direction by a different amount when passing from air to glass or glass to air.
Every wavelength of light is affected to a different degree by the refractive index of a material and as a result changes direction by a different amount when passing from one medium (such as air) to another (such as glass or water).
The refractive index of a medium is calculated using the formula: Where n = refractive index, c = speed of light in a vacuum, v = speed of light in a transparent medium.
The amount that the path of a ray of light bends when it changes direction is calculated using the Law of refraction (also known as Snell’s law).
Chromatic dispersion
Chromatic dispersion is often simply called dispersion.
Whenever you see a rainbow of colours in a patch of oil, in the edge of a sheet of glass or a crystal, it is caused by dispersion.
Dispersion takes place because the refractive index of any transparent medium is different for each wavelength of light.
The diagram at the top of the page shows that in certain circumstances when white light strikes a prism, a rainbow of colours become visible to an observer.
Prism
In the field of optics, a prism is made of glass or other transparent material with flat, polished surfaces.
Prisms are generally made from crown or flint glass depending on their intended use.
Flint glass prisms are often used for experimental purposes to study the refraction and dispersion of light.
A triangular prism consists of two triangular ends and three rectangular faces.
If white light is to be refracted or dispersed by a prism into its component colours a narrow beam is pointed towards one of the rectangular faces.
Dispersive prisms are used to break up light into its constituent spectral colours.
Reflective prisms are used to reflect light, in order to flip or invert a light beam.
Triangular reflective prisms are a common component of cameras, binoculars and microscopes.
Crown glass is a type of optical glass made without lead or iron and used in the manufacture of lenses and other tools and equipment concerned with the visible part of the electromagnetic spectrum.
Crown glass produces low levels of chromatic dispersion which is of particular concern in the manufacture of lenses.
Dispersion is unavoidable but a well-designed lens is able to reorganize light so that, in the end, all wavelengths converge at the same point and so produce a sharp image with a high degree of colour accuracy.
Flint glass
Flint glass is made from a combination of silicon dioxide (SiO2) and lead or potassium.
Flint glass typically has a higher refractive index value than crown glass which means that dispersion is more evident.
Flint glass absorbs most ultraviolet light but comparatively little visible light and is often used in telescope lenses.
The diagram
In this diagram a ray of incident light strikes one of the three rectangular surfaces at an angle so that it exits from the middle of another.
The light source used produces white light which is focused into a narrow beam.
As the ray enters the prism the angles of incidence and refraction are the same.
When the light exits the prism the angles of incidence and refraction are the same.
The light source and prism are arranged on a suitable surface, such as a piece of paper so that the dispersed colours are visible to an observer.
Remember that light is only visible when either its source is in view or when transmitted light strikes a surface, in this case, the paper.
The human eye sees white when all the colours that make up visible light are combined together and strike a neutral coloured surface that reflects all wavelengths equally.
Remember that:
The incident white light is refracted towards the normal as it enters the prism because the optic density of glass is greater than air.
On entry to the prism, a small amount of dispersion takes place.
As the dispersed colours exit the prism they are refracted away from the normal because the optic density of air is less than air.
On exiting the prism, the amount of dispersion of each colour is more pronounced.
The amount that light bends as refraction and dispersion take place depends on:
The type of glass.
The composition of wavelengths produced by the light source.
The spectral colour model represents the range of pure colours that correspond to specific wavelengths of visible light. These colours are called spectral colours because they are not created by mixing other colours but are produced by a single wavelength of light. This model is important because it directly reflects how human vision perceives light that comes from natural sources, like sunlight, which contains a range of wavelengths.
The spectral colour model is typically represented as a continuous strip, with red at one end (longest wavelength) and violet at the other (shortest wavelength).
Wavelengths and Colour Perception: In the spectral colour model, each wavelength corresponds to a distinct colour, ranging from red (with the longest wavelength, around 700 nanometres) to violet (with the shortest wavelength, around 400 nanometres). The human eye perceives these colours as pure because they are not the result of mixing other wavelengths.
Pure Colours: Spectral colours are considered “pure” because they are made up of only one wavelength. This is in contrast to colours produced by mixing light (like in the RGB colour model) or pigments (in the CMY model), where a combination of wavelengths leads to different colours.
Applications: The spectral colour model is useful in understanding natural light phenomena like rainbows, where each visible colour represents a different part of the light spectrum. It is also applied in fields like optics to describe how the eye responds to light in a precise, measurable way.
The Sun is the most important light source in our lives and emits every wavelength of light in the visible spectrum.
Celestial sources of light include other stars, comets and meteors.
Other natural sources of light include lightning, volcanoes and forest fires.
There are also bio-luminescent light sources including some species of fish and insects as well as types of bacteria and algae.
Man-made light sources of the most simple type include natural tars and resins, wax candles, lamps that burn oil, fats or paraffin and gas lamps.
Modern man-made light sources include tungsten light sources. These are a type of incandescent source which means they radiate light when electricity is used to heat a filament inside a glass bulb.
Halogen bulbs are more efficient and long-lasting versions of incandescent tungsten lamps and produce a very uniform bright light throughout the bulb’s lifetime.
Fluorescent lights are non-incandescent sources of light. They generally work by passing electricity through a glass tube of gas such as mercury, neon, argon or xenon instead of a filament. These lamps are very efficient at emitting visible light, produce less waste heat, and typically last much longer than incandescent lamps.
An LED (Light Emitting Diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor.
Made-made lights can emit a single wavelength, bands of wavelengths or combinations of wavelengths.
An LED light typically emits a single colour of light which is composed of a very narrow range of wavelengths.
As light crosses the boundary between two transparent media, the law of refraction (Snell’s law) states the relationship between the angle of incidence and angle of refraction of the light with reference to the refractive indices of both media as follows:
When electromagnetic radiation (light) of a specific frequency crosses the interface of any given pair of media, the ratio of the sines of the angles of incidence and the sines of the angles of refraction is a constant in every case.
Snell’s law deals with the fact that for an incident ray approaching the boundary of two media, the sine of the angle of incidence multiplied by the index of refraction of the first medium is equal to the sine of the angle of refraction multiplied by the index of refraction of the second medium.
Snell’s law deals with the fact that the sine of the angle of incidence to the sine of the angle of refraction is constant when a light ray passes across the boundary from one medium to another.
Snell’s law can be used to calculate the angle of incidence or refraction associated with the use of lenses, prisms and other everyday materials.
When using Snell’s law:
The angles of incidence and refraction are measured between the direction of a ray of light and the normal – where the normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.
Rainbow colours are the colours seen in rainbows and in other situations where visible light separates into its different wavelengths and the spectral colours corresponding with each wavelength become visible to the human eye.
The rainbow colours (ROYGBV) in order of wavelength are red (longest wavelength), orange, yellow, green, blue and violet (shortest wavelength).
It is the sensitivity of the human eye to this small part of the electromagnetic spectrum that results in our perception of colour.
The names of rainbow colours are a matter more closely related to the relationship between perception and language than anything to do with physics or scientific accuracy. While the spectrum of light and the colours we see are both determined by wavelength, it’s our eyes and brains that turn these differences in light into the colours we experience.
In the past, rainbows were sometimes portrayed as having seven colours: red, orange, yellow, green, blue, indigo and violet.
Modern portrayals of rainbows reduce the number of colours to six spectral colours, ROYGBV.
In reality, the colours of a rainbow form a continuous spectrum and there are no clear boundaries between one colour and the next.
Visible light is perceived by a human observer as all the spectral colours between red and violet plus all other colours that result from combining wavelengths together in different proportions.
A spectral colour is produced by a single wavelength of light.
The complete range of colours that can be perceived by a human observer is called the visible spectrum.
The range of wavelengths that produce visible light is a very small part of the electromagnetic spectrum.
Wavelength measures a complete wave cycle, which is the distance from any point on a wave to the corresponding point on the next wave.
While wavelength can be measured from any point on a wave, it is often simplest to measure from the peak of one wave to the peak of the next or from the bottom of one trough to the bottom of the next, ensuring the measurement covers the whole of the cycle.
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