Page 196 - Physics_Form_2

Physics for Secondary Schools

because it reflects green and red lights from as colour mixing. Since colour-
the white incident light. Generally, the rules of mixing uses the concepts of
subtraction of light colour are: addition and subtraction of light
1. Red colour absorbs green and blue light colours, there are two main
and reflects red light. types of colour mixing. These
2. Blue colour absorbs green and red light and are additive colour mixing and
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reflects blue light. subtractive colour mixing.
3. Green colour absorbs blue and red light Additive colour mixing
while reflecting green light.
4. Cyan colour absorbs red light and reflects Additive colour mixing is the
process of creating a new colour
cyan light (blue + green). by adding one set of colours to
5. Magenta colour absorbs green light and another set of colours. When we
reflects magenta light (red + blue). add all of the different colours of
6. Yellow colour absorbs blue light and reflects sunlight, we see white light rather
yellow light (red + green). than many individual colours.
Thus, this type of colour mixing
These rules are very important concepts for is called additive colour mixing
understanding colour appearance in objects. because all of the wavelengths
Figure 5.29 summarises the colour subtraction still reach our eyes, but the
rules. observed colour depends on the

M+Y=RED combinations of different colours.

Yellow subtracts M Magenta Normally, primary colours used
blue Y subtracts green in additive colour mixing are red,
blue and green and secondary

C+Y=GREEN colours are cyan, magenta and
M + C = BLUE yellow. Additive colour mixing
Cyan subtracts C is commonly used to generate
red colours on televisions and
C + M + Y = BLACK computer monitors using RGB
Figure 5.29: Light colour subtraction using (red, green and blue) system.
idealised primary filters Activity 5.10 that you performed
earlier demonstrates the process
Additive and subtractive mixing of colours of additive mixing of colours.
Following our discussion on the addition and
subtraction of colours of light, you may have Subtractive colour mixing
realised that objects can appear in different When colour pigments are mixed,
colours depending on the combination of light both paints continue to absorb
that reaches our eyes. This idea is very useful the same colours as they did
in the synthesis of colours, which we refer to before being mixed, the result is

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Student’s Book Form Two

Physics Form 2 Final.indd 190 25/10/2025 10:28