Dictionary tag: S

Snell’s Law Calculator

To calculate the angle of refraction of an incident ray entering a raindrop enter:

  1. The refractive index of air for a ray with wavelength 589.29 nm. n1) = 1.000293
  2. The refractive index of water for ray with wavelength 589.29 nm, (n2) = 1.3333
  3. The Angle of incidence of your ray as it strikes the surface. (θi) = angle between the ray and the normal

The angle of refraction (θ2) will appear in the final box.

Snell’s Law Calculator

https://www.omnicalculator.com/physics/snells-law

Sine

In mathematics, the sine is a trigonometric function of an angle.

  • The sine of an acute angle is defined in the context of a right-angle triangle.
  • For any specified angle, it’s sine is the ratio of the length of the side opposite that angle, to the length of the longest side of the triangle (the hypotenuse).
  • The mathematical notation for sine is sin.

Subtractive colour

A subtractive colour model combines different hues of a colourant such as a pigment, paint, ink, dye or powder to produce other colours.

  • CMYK is a subtractive colour model.
  • CMYK pigments are the standard for colour printing because they have a larger gamut than RGB pigments.
  • CMYK printing typically uses white paper which has good reflective properties and then adds cyan, magenta, yellow and black ink or toner to produce colour.
  • Highlights are produced by reducing the amount of coloured ink and printing without black to allow the maximum amount of light to reflect off the paper through the ink.
  • Mid tones rely on the brilliance and transparency of the pigments and the reflectivity of the paper to produce fully saturated colours.
  • Shadows are produced by adding black to both saturated or desaturated hues.

Scattering

Scattering takes place when streams of photons (or waves of light) are deflected in different directions.  In this resource, the term is used to refer to the different forms of deviation produced by diffusion, dispersion, interference patterns, reflection and refraction as well as by the composition and surface properties of different media.

Regular scattering
  • When light of a particular wavelength strikes the surface and enters a raindrop its subsequent path depends upon the point of impact, the refractive indices of air and water and the surface properties of the droplet.
  • For incident rays of a single wavelength striking the surface of a single droplet at different points,  it is the different angles at which they enter the droplet that are the chief determinant of the way they scatter as they exit the droplet. In this case.
  • For incident rays of a white light striking the surface of a single droplet at different points, it is the combined effects of the different angles at which they enter the droplet along with the effects of chromatic dispersion (causing the separation of white light into spectral colours) that determine the form of scattering.
  • Chromatic dispersion refers to the way that light, under certain conditions, separates into its component wavelengths and the colours corresponding with each wavelength become visible to a human observer.
  • Regular scattering is not random and obeys the law of reflection and refraction (Snell’s law).
Random scattering
  • In optics, diffusion results from any material that scatters light during transmission or reflection producing softened effects without sharp detail.
  • Objects produce diffuse reflections when light bounces off a rough or uneven surface and scatters in all directions.
  • Transparent and translucent materials transmit diffuse light unless their surfaces are perfectly flat and their interiors are free of foreign material.
  • All objects obey the law of reflection on a microscopic level, but if the irregularities on the surface of an object are larger than the wavelength of light, the light undergoes diffusion.
  • A reflection that is free of the effects of diffusion is called a specular reflection.
  • In the case of raindrops, random scattering can result from:
    • Atmospheric conditions affecting incident sunlight.
    • Turbulence distorting the shape of raindrops.
    • Light being reflected off the surface of multiple raindrops, one after another, before reaching an observer.

Speed of light

The speed (or velocity) of a light wave is a measurement of how far it travels in a certain time.

  • The speed of light is measured in metres per second (m/s).
  • Light travels through a vacuum at 300,000 kilometres per second.
  • The exact speed at which light travels through a vacuum is 299,792,458 metres per second.
  • Light travels through other media at lower speeds.
  • A vacuum is a region of space that contains no matter.
  • Matter is anything that has mass and occupies space by having volume.
  • When discussing electromagnetic radiation the term medium (plural media) is used to refer to anything through which light propagates including empty space and any material that occupies space such as a solid, liquid or gas.
  • In other contexts empty space is not considered to be a medium because it does not contain matter.

Solar radiation

Solar radiation is the electromagnetic radiation emitted by the sun.

  • Electromagnetic radiation is a type of energy that is commonly known as light. Detached from its source, it is transported by electromagnetic waves (or by their quanta, particles called photons) and propagates through space.
  • Electromagnetic radiation includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.
  • Electromagnetic radiation is sometimes called EM radiation or electromagnetic radiant energy (EMR).
  • All forms of electromagnetic radiation can be described in terms of both waves or particles.
  • All forms of electromagnetic radiation travel at 299,792 kilometres per second in a vacuum.

Secondary colour

A secondary colour is a colour made by mixing two primary colours in a given colour space. The colour space may be produced by an additive colour model that involves mixing different wavelengths of light or by a subtractive colour model that involves mixing pigments or dyes.

  • Secondary colours produced by an additive colour model are quite different from the spectral colours seen in a rainbow.
  • A spectral colour is produced by a single wavelength, or a narrow band of wavelengths, within the visible spectrum.
  • A secondary colour produced by an additive colour model results from superimposing wavelengths of light from different areas of the visible spectrum.
  • For the human eye, the best additive primary colours of light are red, green, and blue.

Sunlight

Sunlight is light emitted by the Sun and is also called daylight or visible light.

  • Sunlight is only one form of electromagnetic radiation emitted by the Sun.
  • Sunlight is only a very small part of the electromagnetic spectrum.
  • Sunlight is the form of electromagnetic radiation that our eyes are sensitive to.
  • Other types of electromagnetic radiation that we are sensitive to, but cannot see, are infrared radiation that we feel as heat and ultraviolet radiation that causes sunburn.

Spectral power distribution

The spectral power distribution (spectral distribution) of a light or colour stimulus refers to the range, mixture and intensity of wavelengths of light that it produces.

  • A diagram showing the accurate measurement of the spectral power distribution of the light given off (emitted, transmitted, or reflected) by a light source or by a surface provides complete information about that stimulus.
  • The human eye contains three colour receptors (cones), which means that every spectral power distribution is reduced to three sensory quantities that can be described by tristimulus values.
  • Different stimuli can in some cases produce the same colour sensation for an observer. This effect (called metamerism) occurs because each type of cone responds to the distribution of energy across the entire spectral power distribution of a light source.

Sun

The Sun is the star at the centre of our solar system.

  • The energy emitted by the Sun is called electromagnetic radiation or solar radiation.
  • The solar radiation that the human eye is sensitive to is often called sunlight or visible light.
  • The term light is often used to refer to visible light but can also be used to refer to all the different forms of electromagnetic radiation.