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Refraction and dispersion of light
colours. These include red (R), blue (B) Procedure
and green (G) as shown in Figure 5.23. 1. Cover the opening of the first torch
Moreover, mixing together two or all of with a green filter, the second with
these three primary light colours with a blue filter and the third with a red
varying degrees of intensity can produce filter.
a wide range of other light colours. Many 2. Switch on the torches and ensure that
YellowREADING ONLY
television sets and computer monitors the first torch gives green light, the
produce a wide range of colours on the second gives blue light and the third
monitor by using red, green and blue gives red light.
light-emitting phosphors. 3. Direct the torches to the white screen
such that circles of green, blue and
Red Blue Green red light can be seen on the screen.
4. Slowly move the torches such that
Figure 5.23: Primary light colours
the blue and red circles intersect by
half of their size and observe the
Light colours formed by combining image on the screen. Record your
the primary colours are referred to as observation.
secondary colours. These include cyan, 5. Repeat step 4 for different
magenta, and yellow, as shown in combinations of light circles on the
Figure 5.24.
screen.
FOR ONLINE
6. Now, combine all the three circles
Cyan Magenta such that there is a region of
intersection for all three circles.
Figure 5.24: Secondary light colours Observe the image on the screen.
On the other hand, white light can Questions
sometimes be formed by mixing any two (a) What is the resulting colour in each
colours of the light spectrum. Therefore, case?
the two colours that mix in definite ratios to (b) What is the colour at the region of
form white light are termed complementary intersection when all the three colour
colours. Examples of complementary circles were combined?
colours are blue and yellow, red and cyan, (c) What do your observations mean?
and green and magenta.
Activity 5.10 Different combinations of primary colours
of light produce different secondary
Aim: To investigate the mixing colours. For example, green and blue lights
of primary colours of light combine to produce cyan, which is the
Materials: three torches, light colour complement of red. green and red lights
filters, a white screen, dark combine to produce yellow, which is the
room complement of blue, while blue and red
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Physics Form 2 Final.indd 187 25/10/2025 10:28
