Page 192 - Physics_Form_2

Physics for Secondary Schools

3. View the white object under the filtered light.
4. Observe and record the appearance of the white object under the filtered light.
Questions
(a) Describe the appearance of the white object as seen through each light filter.
(b) What happens when light from the blue filter is passed through a green filter?
Yellow filterREADING ONLY
When white light is transmitted through a colour filter, the filter allows only a specific
light colour to pass through it. Therefore, the filtered light will have a colour depending
on the colour of the filter. For example, the light will be yellow, green, blue or red if
the filter used is respectively yellow, green, blue or red. Consequently, if light from one
filter is passed through another filter of different colour, the light is absorbed by the
second filter. Now, when the light through a filter of a given colour falls on the white
object, the object reflects that light into the observer’s sight. Therefore, the object
appears to have the colour of the filtered light. Figure 5.22 shows the appearance of a
white object under different coloured lights.

White White White White
object object object object

FOR ONLINE
Red filter Green filter Blue filter

(a) Object appears (b) Object appears (c) Object appears (d) Object appears
red yellow green blue

Figure 5.22: Appearance of a white object under coloured lights

Primary, secondary and complementary from the middle, we can produce all the
colours of light colours found in that half of the spectrum.

What happens when a physicist Similarly, by mixing lights from both
simultaneously casts the blue, green and ends of the spectrum with light from the
red light beams on a spot on a white middle, we can generate all the colours
screen? that lie in between them.

Experiments with beams of various White light can also be produced by
coloured lights have demonstrated that combining only three distinct light
many colours in the light spectrum can colours, provided that they are widely
separated on the visible light spectrum.
be created by mixing other colours. Any three colours of light that produce
For instance, when light from one end white light when combined with the
of the spectrum is combined with light correct intensity are called primary

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Student’s Book Form Two

Physics Form 2 Final.indd 186 25/10/2025 10:28