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Questions on colour

Q4. The human eye detects red light, blue light and green light. A combination of red, green and blue light is seen as white. We ‘see’ other colours when different combinations of red, blue and green enter the eye. This is shown in the table.

light entering the eye

 

colour ‘seen’ by the eye

no light

 

black

red

 

red

blue

 

blue

green

 

green

red + blue

 

magenta

blue + green

 

cyan

red + green

 

yellow

red + blue + green

 

white


(a) Some magenta paint is illuminated by a combination of red, green and blue light. Explain why the paint appears magenta.

2 marks

Magenta paint scatters blue and red light but absorbs green light.

(b) A mixture of cyan paint and yellow paint appears green in a combination of
red + blue + green light. Explain what happens to:

(i) the red light?

1 mark

It is absorbed by the cyan paint but scattered by the yellow paint.

(ii) the blue light?

1 mark

It is scattered by the cyan paint but absorbed by the yellow paint.

(iii) the green light?

1 mark

It is scattered by the cyan and yellow paints. Therefore it is the dominant colour.

(c) Most colours of paint can be obtained by mixing different combinations of cyan, magenta and yellow paints. What combination of these paints makes:

(i) blue paint?

Cyan and magenta

(ii) red paint?

Yellow and magenta

2 marks

Maximum 7 marks

 

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