Page 187 - Physics_Form_2

Refraction and dispersion of light

Colours of light
The major source of light for the Earth is the Sun. What is the colour of sunlight?
Sometimes we see in the sky a rainbow consisting of different colours. In addition,
during sunset or sunrise, the sky appears orange or red. Can we conclude from these
observations that sunlight is made of different colours?
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Dispersion of white light
White light is known to consist of seven colours. If a beam of white light is passed
through a triangular glass prism, it splits into a band of seven colours. Figure 5.16 shows
a band of colours formed when white light passes through a triangular glass prism. This
band is known as the spectrum of white light. Colours that form the spectrum of white
light are red (R), orange (O), yellow (Y), green (G), blue (B), indigo (I) and violet
(V). For the sake of remembering the arrangement of these colours, an abbreviation
ROYGBIV is commonly used.

Spectrum
White light

Figure 5.16: Dispersion of white light by a triangular glass prism

Dispersion of light is a phenomenon in shown in Figure 5.16. Each component
which white light splits into its colour has a different wavelength, which
components upon passing through a falls well within the visible part of the
medium such as a triangular glass prism. electromagnetic spectrum.
This phenomenon happens because when
a beam of white light enters a transparent Rainbow
medium, each colour component is Light dispersion can also occur when
refracted at a different angle of refraction, light passes through other transparent
resulting in different angles of deviation. materials, such as water droplets and
For example, red colour deviates least soap bubbles. One consequence of
while violet colour deviates most. The light dispersion by water droplets in the
result is the splitting of the white light atmosphere is the formation of a rainbow.
into its components to form a spectrum A rainbow is a natural phenomenon
with red colour being at the upper part caused by the dispersion of white light. It
of the spectrum, and the violet colour is caused by the refraction and reflection
being at the bottom of the spectrum, as of white light by falling water droplets.

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Physics Form 2 Final.indd 181 25/10/2025 10:28