Apparent Position of a Rainbow

Rainbows appear when bright sunshine is refracted, reflected and dispersed in raindrops in the presence of an observer.

No! Rainbows are not always visible at midday because their whole circumference can be below the horizon when the sun is high in the sky.

Rainbows appear as bands of colour because our eyes tend to see some wavelengths of light as being brighter and so more distinct than others.

Yes! In ideal conditions, atmospheric rainbows produce a continuous spectrum of colours inclusive of all wavelengths of the visible spectrum.

Yes! Other common media that produce rainbow-like effects include: Paraffin Benzene Plate glass Other glass

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.

 

 

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.

Reflection is the process where light rebounds from a surface into the medium it came from, instead of being absorbed by an opaque material or transmitted through a transparent one.

• The three laws of reflection are as follows:
  • When light hits a reflective surface, the incoming light, the reflected light, and an imaginary line perpendicular to the surface (called the “normal line”) are all in the same flat area.
  • The angle between the incoming light and the normal line is the same as the angle between the reflected light and the normal line. In other words, light bounces off the surface at the same angle as it came in.
  • The incoming and reflected light are mirror images of each other when looking along the normal line. If you were to fold the flat area along the normal line, the incoming light would line up with the reflected light.

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.

• The observer effect is a principle of physics and states that any interaction between a particle and a measuring device will inevitably change the state of the particle. This is because the act of measurement itself imposes a disturbance on the particle’s wave function, which is the mathematical description of its state.
• The concept of observation refers to the act of engaging with an electron or other particle, achieved through measuring its position or momentum.
• In the context of quantum mechanics, observation isn’t a passive undertaking, observation actively alters a particle’s state.
• This means that any kind of interaction with an atom, or with one of its constituent particles, that provides insight into its state results in a change to that state. The act of observation is always intrusive and will always change the state of the object being observed.
• It can be challenging to reconcile this with our daily experience, where we believe we can observe things without inducing any change in them.

A human observer is a person who engages in observation by watching things.

• In the presence of visible light, an observer perceives colour because the retina at the back of the human eye is sensitive to wavelengths of light that fall within the visible part of the electromagnetic spectrum.
• The visual experience of colour is associated with words such as red, blue, yellow, etc.
• The retina’s response to visible light can be described in terms of wavelength, frequency and brightness.
• Other properties of the world around us must be inferred from light patterns.
• An observation can take many forms such as:
  • Watching an ocean sunset or the sky at night.
  • Studying a baby’s face.
  • Exploring something that can’t be seen by collecting data from an instrument or machine.
  • Experimenting in a laboratory setting.

 

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.