Wednesday, 25 January 2017
The effect of electromagnetic vibrations depends upon their frequency. If the force vibrates around 430 million million times a second then it will interact with your eyes and you will see it as red light; as it vibrates faster it appears as the other colours of the spectrum- orange, then yellow, green, blue, and indigo- until about 770 million million times a second when it appears violet. When it vibrates faster than that you can’t see it. We then give it names such as ultraviolet, x-rays, and gamma rays as the frequency of vibration increases (the names are a hang-over from the days before we realised that they were all electromagnetic vibrations differing only by the rate of the vibration).
When the vibration is less than 430 million million times, the waves again become invisible, and we give them the following names broadly according to how slowly they vibrate: infrared, microwaves, UHF, VHF, short wave, medium wave and long wave.
Broadcast TV signals, for example, are just electromagnetic vibrations that vibrate about a million times less often than visible light. When the waves pass your TV aerial they make electrons in the aerial move back and forth, and that movement is ultimately detected and decoded by your TV.