Em waves are self sustaining

In summary, it is said in articles that EM waves are self-sustaining, making them appear as perpetual motion. However, perpetual motion is allowed as long as no external energy is harnessed or work is extracted. This is possible for EM waves in a vacuum, but not if energy is extracted from them. In an ideal scenario, a superconducting ring could also exhibit perpetual motion until work is extracted from it.
  • #1

wolram

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in all the articles i have read it is said that em waves are self sustaining, if this is corect then they are perpetual motion, i thought that was not allowed??
 
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  • #2
Photons do not have mass. That means that they move
through space but not through time - that means they
always have the speed(of light) c according to relativity.

Live long and prosper.
 
  • #3


Originally posted by wolram
in all the articles i have read it is said that em waves are self sustaining, if this is corect then they are perpetual motion, i thought that was not allowed??

I believe that perpetual motion is allowed in the sense that it does not violate any physical laws. What is not allowed is a "Perpetual Motion Machine" that runs forever and also does work.

You can have a process continue indefinitely without an external source of energy as long as you do not harness it or extract work from it. There must be no loss either--as for example due to friction or air resistance: which can be thought of as doing undesired work like heating something by rubbing or stirring up the air. To continue, the process must do no work.

Light or EM waves can travel indefinitely in a vacuum, but if one sticks solar cells in their path to extract electricity then their motion stops being perpetual

I suppose in an ideal superconducting ring you could start current flowing around the ring and then put the ring in an perfectly insulated box and the current would keep on circulating around the ring forever. Or until someone tried to get some work out of it.
 
  • #4
how daft of me, thanks...
 

1. What does it mean for EM waves to be self-sustaining?

Self-sustaining EM waves are waves that can propagate and maintain their energy without the need for an external source. This is because the electric and magnetic fields in the wave can regenerate each other, allowing the wave to continue propagating indefinitely.

2. How do EM waves sustain themselves?

EM waves sustain themselves through the interaction between the electric and magnetic fields. As the electric field changes, it creates a magnetic field, which in turn creates an electric field, and this cycle continues as the wave propagates through space.

3. Are all EM waves self-sustaining?

No, not all EM waves are self-sustaining. Only electromagnetic waves that are in a vacuum or in a medium that has no loss can sustain themselves. In other words, any energy lost due to resistance or absorption will not be replenished, and the wave will eventually dissipate.

4. Can EM waves be self-sustaining in all types of mediums?

No, self-sustaining EM waves can only exist in mediums with no loss. In materials with loss, such as metals, some of the wave's energy will be absorbed and converted into heat, causing the wave to eventually dissipate.

5. What are the practical applications of self-sustaining EM waves?

Self-sustaining EM waves have many practical applications, including wireless communication, radar systems, and medical imaging. They are also used in power generation and transmission, as well as in various scientific research and technology development projects.

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