Interactive Primary Newsletter 34 Nothin' but blue sky....

Black and white ‘White light’ is an idea used by Newton to describe sunlight (Fig. 15). From his experiments with prisms, Newton had shown that sunlight is composed of all the colours of the spectrum. White light is now the term used to describe the mixture of colours found in sunlight. Why are the unprinted parts of a magazine white? This is for two reasons. Firstly you are reading it in sunlight or artificial lighting equivalent to sunlight in its mixture of colours and secondly all these colours are reflected and scattered equally well off the surface of the paper. Why is snow white? Because it reflects and scatters all colours of daylight equally well. Figure 15 - White light Black is the opposite to white. Blackness is an absence of light. A black surface emits no light, or so little light that you are unaware of any because of contrast effects. Here’s something else to try. The mug in the illustration has a white interior when seen in daylight (Fig. 16). You will need a mug similar to this and a piece of card through which a pencil has been poked to make a hole. Figure 16 - Mug with white interior   Sit the card over the mug (Fig. 17). What colour is the interior? It is now black. There is almost no light getting into it. Therefore there is almost none getting out. Therefore when you look at the hole it is black and when you peer inside it is also black. Figure 17 - Same mug with black interior