White light is a mixture of electromagnetic radiation at different wavelengths. The human eye is sensitive to wavelengths between roughly 380 nanometres (nm) and 750 nm with its maximum sensitivity being at about 555 nm. Other species, such as certain insects, are sensitive to different wavelengths of light e.g. ultraviolet (a short video worth watching!)
The different wavelengths correspond to the different colours of the light; other colours are made by subtle mixtures of different wavelengths. Colours that can be produced by just a single wavelength of light are called pure spectral colours.
Although there is no clear mark when one colour becomes another, the above table shows a good approximation of where the divisions lie.
The shorter wavelengths have a higher frequency and are refracted more when they pass from air into water or glass. This means that a prism can be used to split white light into its spectrum of colours.
I hope I have not pitched the following video at too high a level for you – it is Ludvig von Drake.
Of course, you will have screamed at the video, “The red apple would have been black under the blue & green lights!” Red apples absorb all wavelengths of light except red, which they reflect.
Now a couple of questions for you to answer in the comments section below.
- Wavelength affects the colour of light, but what property of sound is changed by its wavelength?
- What is the speed of light? (Your choice of units)
- What secondary colour of light is produced when blue and green overlap?
- What colour would a yellow ball appear to be when lit with green light?
- A nanometre (nm) is one billionth of a metre. What is 555 nm in mm?
- What name is given to the bending of light that happens as it passes from one medium to another?
- [Extension] How can we use the light from distant stars to tell if they are moving towards us or away from us? And how does the spectrum of the light tell us something about the atoms inside the star?
Comments