Everything Science Grade 12

10.4 CHAPTER 10. COLOUR

Colours on a TelevisionScreen ESCEU

If you look very closelyat a colour cathode-raytelevision screen or cathode-ray com-

puter screen, you willsee that there are verymany small red, greenand blue dots

called phosphors on it. These dots are caused to fluoresce (glow brightly) when a beam

of electrons from the cathode-ray tube behindthe screen hits them. Since different

combinations of the three primary colours of light can produce any other colour, only

red, green and blue dots are needed to make pictures containing all thecolours of the

visible spectrum.

Exercise 10 - 2

1. List the three primarycolours of light.


2. What is the term forthe phenomenon whereby white light is split up into its
   different colours by a prism?


3. What is meant by theterm “complementary colour” of light?


4. When white light strikes a prism which colour of light is refracted the most and
   which is refracted the least? Explain your answer in terms of the speed of light in
   a medium.

More practice video solutions or help at http://www.everythingscience.co.za

(1.) 01i1 (2.) 01i2 (3.) 01i3 (4.) 01i4

10.4 Pigments and Paints ESCEV

We have learnt that white light is a combination of all the colours of the visible spec-

trum and that each colour of light is related toa different frequency. But what gives

everyday objects aroundus their different colours?

Pigments are substanceswhich give an object itscolour by absorbing certain frequen-

cies of light and reflecting other frequencies. For example, a red pigment absorbs all

colours of light except red which it reflects. Paints and inks contain pigments which

gives the paints and inks different colours.