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Physics for Secondary Schools
combine to produce magenta, which Addition of colours of light
is the complement of green. Thus, two Generation of various colours of light by
primary colours combine to produce the mixing of the three primary colours of light is
complement of the third primary colour, known as colour addition. The colour addition
whereas the three primary colours principles can be used to make predictions of
combine to produce white light. One the colours that would result when different
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can easily remember the combinations coloured lights are mixed. For example, red
of primary colours of light by observing (R) light and green (G) light add together
the circles in Figure 5.25. to produce yellow (Y) light. Red light and
blue light add together to produce magenta
(M) light. Green light and blue (B) light add
together to produce cyan (C) light. Finally, red
Green light, green light and blue light add together
Yellow
to produce white light. Moreover, addition
Cyan Red of complementary colours of light produces
white light. The addition of light colours can
Majenta be described by the following equations;
Blue
R + G = Y
R + B = M
G + B = C
Figure 5.25: Mixing primary colours
R + C = R + (G + B) = W
Addition and subtraction of light B + Y = B + (G + R) = W
colours G + M = G + (R + B) = W
When you look at an object and
perceive a distinct colour, you are not Note that, Figure 5.26 can conveniently
necessarily seeing a single colour of summarise the colour addition equations.
light, rather a combination of different
colours. Consider, for instance, that Red
you are looking at a shirt that appears
yellow. There may be several colours Magenta Yellow
of light with varying intensity that
strike your eye after being reflected
by the shirt. Yet your eye-brain system
interprets the colours that strike your Blue Green
eye, and the shirt is perceived to be
yellow. Understanding how different
colours are perceived requires Cyan
knowledge of adding and subtracting
light colours. Figure 5.26: Addition of light colours
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Student’s Book Form Two
Physics Form 2 Final.indd 188 25/10/2025 10:28
