The Electromagnetic Spectrum

Electromagnetic radiation is constituted by radiation of all possible frequencies within the Electromagnetic Spectrum; divided into seven major categories: radio waves, microwaves, infra-red waves, visible light, ultra-violet rays, X-rays and gamma rays, in order of increasing frequency and decreasing wavelength. This radiation, more often than not, takes the form of waves, that propagate (travel) through space (vacuum) at the speed of light (c), and through other materials a bit slower.

Wavelength and frequency are but two defining properties of every wave. Wavelength, λ [lambda],  refers to the distance between two adjacent peaks. Or troughs. Or “2 points on a wave in phase with each other”, but we can look at that one later. This length is representative of the objects (or gaps between objects) around which the wave can manoeuvre itself. It is measured in metres (m).

Frequency, f, is the number of wavelengths that pass over a particular point in space in one second (1 s). In pronciple, ot respresents energy – the higher the frequency, the more energy is carried by the wave. It is measured in Hertz (Hz) or “per second”.

c, λ and f are related as such:

c = fλ

you will need this one so remember it!

As c is constant, f and λ are inversely proportional, meaning that high frequency waves generally have short wavelengths, and vice versa. One may also conclude from the fact that one of the units for frequency is “per second”, frequency is related to time as follows:

f = 1/T

where T is time, measured in seconds.

As for the uses of the different types of waves, I would point you either to the picture included in the previous post or the slightly more, er, legible one below. In these cases I believe images do the work better than words.

Electromagnetic Spectrum (Courtesy of Virginia University, clickable!)
Electromagnetic Spectrum (Courtesy of Virginia University, clickable!)

Now, aside from me (and other people) telling you so, why would you believe all this? How can we separate waves in a visible manner? Well, try this: (adapted from TV show Backyard Science)

You will need a cardboard box (a shoe box will be fine), some 3D glasses (the ones sometimes used for watching 4D films, ironically), scissors, clear sellotape and different types of light, e.g torches, desk lamps, UV lights, and provided you take care, matches.

Cut the lenses out of the 3D glasses. On opposite sides of the box, draw around one lens, and cut out a lens-shaped hole. Use the tape to stick the lenses on the box, such that the holes are covered. Shine each light at one of the lenses whilst looking through the box with the other lens. What do you see?

Note: The 3D glasses refract (bend) the different wavelengths by different angles, so you should be able to see the colours that make up each light.

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