Contents
Physics Topics such as mechanics, thermodynamics, and electromagnetism are fundamental to many other scientific fields.
What are the Three Primary Complementary Colors?
Colour of Different Bodies
Coloured objects whether opaque or transparent do not really possess any colour of their own. The colour emitted by them depends on
- the colour of the incident light and
- the pro-portion of light absorbed by them.
Colour Of Opaque body: An opaque body appears in that colour, which is reflected by the body. A red rose appears red in white light since it absorbs all colours of white light except red which is reflected to the observer’s eye. The red rose will appear bright red in red light but black in all other lights-blue, green, yellow, and so on, because it absorbs all the colours of light except red.
It should be noted that black or white is not any special colour. A body appears black if no light is reflected from it and a body appears white in white light if it reflects all the components of white light.
The black cloth of an umbrella looks black because when white light is incident on it, all the components of it are absorbed by it i.e., no colour is reflected from the cloth of the umbrella. Again a white cloth looks white since it reflects all components of white light and absorbs none.
It may be noted as a warning that costly coloured clothes should not be purchased at night. To identify the actual colour of clothes it is to be viewed in sunlight. The artificial light used in shops is not perfectly white. One or the other of the components of white light remains absent. As for example, in the light of a gas-lamp blue colour is generally absent. So the dress which looks blue in sunlight looks black in the light of a gas-lamp.
Colour of a transparent body: when white light falls on a transparent body, it absorbs certain components and transmits the remaining portions which account for its colour. Thus, a transparent plate of red glass appears red, since it absorbs almost all the colours of white light except red which is transmitted by it and this transmitted colour falling on the eye gives the impression of the colour of the glass plate. Hence, objects like these emit that colour of white light which they do not absorb.
If white light is allowed to fall on a red glass plate, and if a blue glass plate is held in the path of red light, it follows as no red light can pass through the blue glass, the two plates together cut off all the light. So the combination of the two glass plates looks dark i.e., black.
Colour of some transparent objects are not pure. For instance, a piece of yellow transparent glass transmits not just yellow but red and green colour light to pass through it as well. Consequently, a red or green object does not appear black when it is seen through an yellow coloured glass.
Again, when we ground a piece of coloured transparent body, its colour fades. In other words, in its powdered/ground state it appears almost white, because, the incident light is repeatedly reflected by the different layers of minutely ground particles. But light can be absorbed only when it penetrates the object to some extent.
In a ground or powdered state, the thickness of the parti-cles is less and so light enters from one side of the particle and exits through the other. Obviously, the more finely you ground the coloured transparent body the more white it will appear in its powdered form due to diffused reflection. From our everyday experience we know that ordinary deep water appears greenish but it may appear dark when the depth is comparatively large.
A very thin plate of metal appears to be of different colours in reflected and transmitted light. This is because of selective reflection. For e.g., an extremely thin gold plate reflects red, orange or yellow colour. So, light that emerges from this plate contains a greater number of green, blue and violet light rays. Suppose, a thin gold plate is illuminated by a white light. If light reflected from the plate reaches the eye it will appear orangish- yellow in colour. Again, if light ray that emerges from the plate reaches the eye, then it will appear greenish-blue in colour.
Primary and Complementary Colours
We know that white light is made of the seven colours of the spectrum in right proportion. So these seven colours are called pure colours. But in fact, other colours can be obtained by com-bining three special colours from among the seven colours of the spectrum. But these three colours cannot be prepared from any other colours. These three colours are red, green and blue.
So, these three colours are called primary colours, e.g. by mixing red and green we can obtain yellow colour. Magenta is obtained by mixing red and blue. It is to be noted that the colour obtained by mixing primary colours is not a pure colour. For example, the yellow obtained by mixing red and green is not a pure colour, because if this yellow colour is incident on a prism, red and green colour will be obtained, due to dispersion.?
Physicists Maxwell, Helmholtz, Konig, et al performed various experiments to prove that by mixing two or more primary colours a new colour could be obtained. They set up a white screen and then allowed three beams of light rays with the pri-mary hues—red, blue and green, to be incident on it i.e., each beam partially overlapped the other two on incidence [Fig.],
The colour obtained by mixing the primary colours is shown in the Fig. e.g.,—
red + green = yellow
red + blue = magenta
blue + green = peacock blue
red + peacock blue = red + blue + green = white
green + magenta = green + red + blue = white
blue + yellow = blue + red + green = white
Again for preparation of white colour all the three primary colours are not always required. By mixing any two colours white colour can be prepared. Any two spectral colours which on mixing together gives the sensation of white are known as complementary colours. For example, white colour is obtained by mixing yellow and blue or green and magenta. So yellow-blue and green-magenta are complementary colours.
After washing of white clothes often blue dye is used because white clothes appear a bit yellow after many wash. Since blue and yellow are complementary colours, the clothes turn white if it is dyed in blue.