Light and its transmission

There are many bodies within the Universe that produce energy spontaneously and emit it as light. The stars are perfect examples of this, our Sun is one of these stars.

Light is made up of electromagnetic waves which travel at a speed of about 300000 kilometres per second, the maximum speed allowed by nature: in other words in one second they travel the same distance that a person would, if he/she were to walk non-stop for 9 years!

The figure represents the typical shape of a wave. If we could walk on top of the wave it would be like walking in the desert: going continually up and down sand dunes. In the figure all the sand dunes are the same height and the distance between them is the same. The constant distance between two dunes, or in more general terms, between two peaks, is called a wavelength.

When we speak about electromagnetic waves, the wavelengths have very different values: indeed, there are wavelengths which are billions of times smaller than a centimetre, or rather billions of times smaller than the length of our little finger’s fingernail. However, the human eye cannot perceive all waves, but only those wavelengths that are included in a very restricted interval, this will be explained on the next page.

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