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Refraction and dispersion of light
the colour that both pigments reflect in
common. This process is therefore called Activity 5.11
subtractive colour mixing because,
when colour pigments mix, each may Aim: To explore the subtractive
absorb some of the colours that the other colour mixing
pigment reflects, reducing the range of Materials: three colours of paint (blue,
FOR ONLINE READING ONLY
colours seen compared to before mixing. red and yellow), plain white
Since we only see light that is reflected papers, a stick, a dropper
by the paints, the primary colours in
the subtractive colour mixing are cyan, Procedure
magenta and yellow while secondary 1. Put a few drops of blue paint on the
colours are red, blue, and green. Even white paper.
addition of primary colours gives black 2. Using a clean dropper, put a similar
colour, which simply means all colours number of yellow paint drops on the
have been absorbed and no light is same paper. This makes an even mixing
reflected. Subtractive colour mixing ratio.
is commonly used in coloured printers 3. Gently mix the paints and observe
and production of different paints using the resulting colour. Record this
a CMY (cyan, magenta and yellow) observation.
system. 4. Repeat the procedure for different
paints, different number of paints and
It is important to note that each primary different mixing ratios.
colour of paint pigment absorbs one
primary colour of light. The colour Question
absorbed by a primary colour paint Explain how new colours have been
pigment is the complementary colour generated by mixing different paints.
of that paint pigment. That is,
(a) Magenta paint absorbs green light. When different paints are mixed, each
(b) Cyan absorbs red light. paint reflects the same light colours that
(c) Yellow absorbs blue light. it was reflecting before being mixed.
However, in the mixture, each paint
On the other hand, each secondary absorbs some of the colours that are
colour paint pigment absorbs two reflected by the other paint. Consequently,
secondary colours of light. That is, only the remaining colours of light reach
(a) Blue paint absorbs cyan and the observer’s eye giving the mixture of
magenta. paints a different colour appearance.
(b) Green paint absorbs yellow and
cyan. Note that, both additive and subtractive
(c) Red paint absorbs magenta and colour mixing are of paramount
yellow. importance for understanding our
perception of different colours.
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