Page 13 - GALIET PHYSICS BLOSSOMS III

In summary, we have found that a particle, which has an electric charge, will have an electric field emanating from it in all directions. We also found that a magnetic field acting on a coil of wire passing through it, will create electron movement which is know as electric current. In short, electric and magnetic field are inextricably linked to each other. “A change in either one necessarily creates the other.”5
(iii) Light is an example of an electromagnetic wave. Give a brief explanation of why there must be waves in an EM field, and show what they look like.
Light is an electromagnetic transverse wave unlike any other wave we experience. Familiar waves always move through some matter (pond waves move through water; sound waves move through air) causing matter to vibrate allowing the waves to send energy from one place to another. By contrast, when light travels through space, we do not witness anything moving up or down because light waves are vibrations of both electric and magnetic fields.6
Moving charged particles create disturbances consisting of electric and magnetic fields moving together through space. These electric and magnetic fields are always perpendicular to each other and to the direction in which the wave journeys. Because they are not independent from each other, they share in different aspects of electromagnetism, in that both electric and magnetic fields form an electromagnetic wave, which carries energy and information from one part of the cosmos to the other. For example, when the charged particles of a star move around, their electric fields change. As a result, the electromagnetic ripples travelling outwards as waves through space do not need a medium in which to move. When our eyes or experimental equipment have been charged with small particles, these respond to the changes in the electromagnetic field by vibrating harmoniously with the received radiation. This is precisely how we see, and how we perceive radiation.7
In simpler terms, just as a pond’s waves will cause a leaf to bob up and down, the electric field’s vibration in an electromagnetic wave will cause an electron to bob up and down. The electrons, if placed in a row, would wriggle as if a snake when light passed by. The distance between wave peaks in this electron row defines the light wave’s wavelength, while the number of times each electron bobs up and down gives us the frequency.8
5 Chaisson, McMillan. Astronomy Today. Volume II. The Solar System. 62.
6 Bennet, Donahue, Schneider, Voit. The Cosmic Perspective. 6th Edition. 146-147. Including Figures 5.5.
7 This paragraph has been gathered from studying Chaisson, McMillan. Astronomy Today. Volume II. The Solar System. 62. 8 Bennet, Donahue, Schneider, Voit. The Cosmic Perspective. 6th Edition. 146-147. Including Figures 5.5.
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