Some Properties of Matter. Грекова О.А. - 15 стр.

                                                15

III Reading:

Read the text; Find out the examples of passive forms.

                                                  Light

        Three hundred years ago Isaac Newton carried out a fundamental experiment with the
prism. Newton’s experiment proved that a ray of a particular spectral colour was refracted by a
particular amount by a prism of a particular glass. Newton proved this by making a small hole
in the screen and arranging its position so as to allow one colour of the spectrum only. This
beam fell on a second prism and measurement showed that this prism refracted it by exactly
the same amount as the first prism had done. The true physical difference between the different
spectral colours was in this way demonstrated by a difference of the amount by which they
were bent by the glass, called a difference of refrangibility
        Before Newton it was believed that white light, the natural light, was simple and that all
colours were complications. Newton showed that white light was the complicated thing, made
up of spectral colours blending into one another, and that each spectral colour and grade of
colour had a definite refrangibility. Thus an ordinary coloured body, say a red rug, is not red
because it adds something to the white light falling on it, but because it absorbs all the spectral
colours of the white light except the red, which it lets go back.
        If we mix yellow and blue paint we get a green paint, because the yellow, which in the
case of paints is not a pure spectral colour, absorbs all the spectral colours, except the yellow
and some of the neighbouring green. While the blue, which is likewise not a pure spectral
colour, absorbs all the spectral colours, except the blue and some of the neighbouring green.
Only the green, then, is left unabsorbed by the mixture. It follows that a red flower will look
black if illuminated by bright blue light, since it absorbs all the blue end of the spectrum.
        Ordinary colours are called subtraction colours. If we throw a yellow beam and a blue
beam of light so as to overlap on a piece of white paper we get a true addition colour, which is
whitish, and not at all green. It is a strange fact that a white colour can be produced by the
addition of two spectral colours, for instance orange and blue. Such colours are called
complementary colours. Most colours that occur in nature are not pure spectral colours: thus
natural yellow - say the yellow of the flower – contains some green and often some red and
orange; different browns are mixture of red, orange, and yellow spectral light in different
proportions.
        The colours of the rainbow are due to the different refraction of the different colours
that make up sunlight by a widespread cloud of tiny water- drops hanging in the skies. On a
clear sunny day, if you stand with your back to the sun and get a cloud of drops made well up
in the air in front of you by squirting water, you can see an artificial rainbow.


                                        Comprehension check:
                           These are the answers. What are the questions?
          a)   When ……………………………? (3 hundred years ago)
          b)    What ……………………………? (He proved that a ray of particular spectral
               colour was refracted by ………)
          c)   What …………………………? (The true physical difference between the
               different spectral colours was ……..)
          d)    ………………………………? (No, white light was the complicated thing)