Refraction & Dispersion

Yes! When light leaves a vacuum or travels from one transparent medium into another, it undergoes refraction causing it to change both direction and speed.

As light travels from a fast medium such as air to a slow medium such as water it bends toward 'the normal' and slows down. As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from 'the normal' and speeds up.

Refraction refers to the way light changes speed and direction as it travels across the interface between one transparent medium to another.

No! A slow transparent medium is optically denser than a rare medium. Conversely, a fast transparent medium is optically rarer than a dense medium.

Chromatic dispersion refers to the way that light separates into its component wavelengths (and so colours), under certain conditions.

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.

A wave diagram is a graphic representation, using specific drawing rules and labels, that depicts variations in the characteristics of light waves. These characteristics include changes in wavelength, frequency, amplitude, speed of light and propagation direction.

• A wave diagram provides a visual representation of how a wave behaves when interacting with various media or objects.
• The purpose of a wave diagram is to illustrate optical phenomena, including reflection, refraction, dispersion, and diffraction.
• Wave diagrams can be useful in both theoretical and practical applications, such as understanding the basics of the physics of light or when designing complex optical systems.

Refraction refers to the way that electromagnetic radiation (light) changes speed and direction as it travels across the boundary between one transparent medium and another.

• Light bends towards the normal and slows down when it moves from a fast medium (like air) to a slower medium (like water).
• Light bends away from the normal and speeds up when it moves from a slow medium (like diamond) to a faster medium (like glass).
• These phenomena are governed by Snell’s law, which describes the relationship between the angles of incidence and refraction.
• The refractive index (index of refraction) of a medium indicates how much the speed and direction of light are altered when travelling in or out of a medium.
• It is calculated by dividing the speed of light in a vacuum by the speed of light in the material.
• Snell’s law relates the angles of incidence and refraction to the refractive indices of the two media involved.
• Snell’s law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the refractive indices.

ROYGBV are the initials for the sequence of colours that make up the visible spectrum: red, orange, yellow, green, blue, and violet.

• The visible spectrum refers to the range of colours visible to the human eye.
• White light, when passed through a prism, separates into a sequence of individual colours corresponding with ROYGBV which is the range of colours visible to the human eye.
• White light separates into ROYGBV because different wavelengths of light bend at slightly different angles as they enter and exit the prism.
• ROYGBV helps us remember the order of these spectral colours starting from the longest wavelength (red) to the shortest (violet).
• A rainbow spans the continuous range of spectral colours that make up the visible spectrum.
• The visible spectrum is the small band of wavelengths within the electromagnetic spectrum that corresponds with all the different colours we see in the world.
• The fact that we see the distinct bands of colour in a rainbow is an artefact of human colour vision.

The refractive index (index of refraction) of a medium measures how much the speed of light is reduced when it passes through a medium compared to its speed in a vacuum.

• Refractive index (or, index of refraction) is a measurement of how much the speed of light is reduced when it passes through a medium compared to the speed of light in a vacuum.
• The concept of refractive index applies to the full electromagnetic spectrum, from gamma-rays to radio waves.
• The refractive index can vary with the wavelength of the light being refracted. This phenomenon is called dispersion, and it is what causes white light to split into its constituent colours when it passes through a prism.
• The refractive index of a material can be affected by various factors such as temperature, pressure, and density.

Incident light refers to light that is travelling towards an object or medium.

• Incident light refers to light that is travelling towards an object or medium.
• Incident light may come from the Sun, an artificial source or may have already been reflected off another surface, such as a mirror.
• When incident light strikes a surface or object, it may be absorbed, reflected, refracted, transmitted or undergo any combination of these optical effects.
• Incident light is typically represented on a ray diagram as a straight line with an arrow to indicate its direction of propagation.

The refractive index (index of refraction) of a medium measures how much the speed of light is reduced when it passes through a medium compared to its speed in a vacuum.

• Refractive index (or, index of refraction) is a measurement of how much the speed of light is reduced when it passes through a medium compared to the speed of light in a vacuum.
• The concept of refractive index applies to the full electromagnetic spectrum, from gamma-rays to radio waves.
• The refractive index can vary with the wavelength of the light being refracted. This phenomenon is called dispersion, and it is what causes white light to split into its constituent colours when it passes through a prism.
• The refractive index of a material can be affected by various factors such as temperature, pressure, and density.

Wavelength is the distance from any point on a wave to the corresponding point on the next wave. This measurement is taken along the middle line of the 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 a whole wave cycle.
• The wavelength of an electromagnetic wave is usually given in metres.
• The wavelength of visible light is typically measured in nanometres, with 1,000,000,000 nanometres making up a metre.
• Each type of electromagnetic radiation – such as radio waves, visible light, and gamma waves – corresponds to a specific range of wavelengths on the electromagnetic spectrum.

In physics and optics, a medium refers to any material through which light or other electromagnetic waves can travel. It’s essentially a substance that acts as a carrier for these waves.

• Light is a form of electromagnetic radiation, which travels in the form of waves. These waves consist of oscillating electric and magnetic fields.
• The properties of the medium, such as its density and composition, influence how light propagates through it.
• Different mediums can affect the speed, direction, and behaviour of light waves. For instance, light travels slower in water compared to a vacuum.
• Examples of Mediums:
  • Transparent: Materials like air, glass, and water allow most light to pass through, with minimal absorption or scattering. These are good examples of mediums for light propagation.
  • Translucent: Some materials, like frosted glass or thin paper, partially transmit light. They allow some light to pass through while diffusing or scattering the rest.
  • Opaque: Materials like wood or metal block light completely. They don’t allow any light to travel through them.

In the field of optics, dispersion is shorthand for chromatic dispersion which refers to the way that light, under certain conditions, separates into its component wavelengths, enabling the colours corresponding with each wavelength to become visible to a human observer.

• Chromatic dispersion refers to the dispersion of light according to its wavelength or colour.
• Chromatic dispersion is the result of the relationship between wavelength and refractive index.
• When light travels from one medium (such as air) to another (such as glass or water) each wavelength is refracted differently, causing the separation of white light into its constituent colours.
• When light undergoes refraction each wavelength changes direction by a different amount. In the case of white light, the separate wavelengths fan out into distinct bands of colour with red on one side and violet on the other.
• Familiar examples of chromatic dispersion are when white light strikes a prism or raindrops and a rainbow of colours becomes visible to an observer.