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k9b4
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EM field strength dies quickly with distance, what's so special about going up and down that allows EM waves to maintain their energy over infinite distance?
What? Strength of electric field dies out quickly with distance. Why does the strength of an electric field going up and down not die out quickly with distance?Simon Bridge said:EM waves retain their total energy in accordance with the law of conservation of energy.
How does a changing magnetic field generate a changing electric field and vice versa?Simon Bridge said:The electric field in the EM waves propagates because it is being generated by a changing magnetic field. In the static case, there is no changing magnetic field to generate more electric field. But it is difficult to see what you are asking - in general, the amplitude of an EM wave will decrease with distance from the source.
k9b4 said:How does a changing magnetic field generate a changing electric field and vice versa?
But I am looking for a physical explanation, not a mathematical one.Nugatory said:The relationship between the electrical and magnetic fields at any given point in space is given by Maxwell's equations. Google for "Maxwell equations", but be prepared to deal with a fair amount of vector calculus.
k9b4 said:But I am looking for a physical explanation, not a mathematical one.
... mathematics is the language of physics - mathematical explanations are the physical ones. All the others are artistic answers.But I am looking for a physical explanation, not a mathematical one.
... Which I cannot interpret because I lack knowledge of mathematicse.bar.goum said:The physical explanation is just going to be Maxwell's equations written out as a sentence. The physical explanation you want is encoded in the mathematics.
... and we cannot help you unless you are prepared to acquire the knowledge ;)Which I cannot interpret because I lack knowledge of mathematics
... Which is why I come to a physics forum for help
It wouldn't be perfectly spherical though would it? Because the point charge in oscillating in one plane?NTW said:The light will propagate as a spherical shell
I do accept that this happens. I am asking why it happens.Simon Bridge said:You'll just have to accept that EM waves travel through space is a fact of Nature which has been empirically confirmed.
For my own understandingSimon Bridge said:What do you need to know for?
k9b4 said:... Which I cannot interpret because I lack knowledge of mathematics
... Which is why I come to a physics forum for help
k9b4 said:It wouldn't be perfectly spherical though would it? Because the point charge in oscillating in one plane?
(...)
Thanks, this is more what I was looking for. I know that the change in the field is what is traveling.Simon Bridge said:I was building Drakkith's answer, but the question is more about propagation so anticipating...
... mathematics is the language of physics - mathematical explanations are the physical ones. All the others are artistic answers.
Imagine we can suddenly switch on a point charge. (Worry about how we may do that later.)
We do this at t=0, relativity means that it takes some time for the electric field to reach farther out. It takes 1s to reach 1 light-second away and so on (electric fields travel at the speed of light.)
This is a time-varying electric field, and the change in the field is what travels out.
Any changing electric field is accompanied by a changing magnetic field and vice versa.
(That's actually two of Maxwell's equations.)
All this is pretty inadequate but it may help you get a glimmering.
But it would not be perfectly spherical right? Because if the point charge is oscillating vertically, then directly above the point charge there would be no change in electric field?NTW said:It doesn't matter, perfectly spherical or not, for the purpose of the mental experiment.
... this is false....an unchanging electric field does not affect things an infinite distance away, ...
Note: if you had an oscilating electric charge, and it was oscillating vertically, then that implies there is gravity. You don't want to include gravity, that's an un-needed complicaton. But we do need a label for the oscillation axis and "oscillation axis" is a bit much to write. Let's say the charge bobs up and down on the z-axis. We can pick the +z direction as the direction of the first displacement.if the point charge is oscillating vertically, then directly above the point charge there would be no change in electric field?
So do the not-oscillating electrons on Earth affect the electrons on the moon?Simon Bridge said:... this is false.
This is because your hand is overall neutral and forces on positive and negative forces cancel. If you somehow removed all the electrons from the solar system, the electrical forces between the remaining nuclei woul be orders of magnitude stronger than the gravitational forces.k9b4 said:So do the not-oscillating electrons on Earth affect the electrons on the moon?
My hand is not repelled from my desk until I get very close to it.
Oh yeah, I didn't think of that.Orodruin said:This is because your hand is overall neutral and forces on positive and negative forces cancel. If you somehow removed all the electrons from the solar system, the electrical forces between the remaining nuclei woul be orders of magnitude stronger than the gravitational forces.
k9b4 said:Oh yeah, I didn't think of that.
So then, could you please explain, why, if we have an electron surrounded by atoms, does it not affect far away things. But as soon as we start oscillating that same electron, far away things are now affected?
In principle - in principle, this is the case yes.k9b4 said:So do the not-oscillating electrons on Earth affect the electrons on the moon?
What do you mean for?Simon Bridge said:It would help us make better answers if you told us what the information was for.
There is nothing special about an electron. The important thing is charge density and current density. If you have a net charge then you will get a field from static charges. If you have a net current then you will get a field from the current.k9b4 said:why, if we have an electron surrounded by atoms, does it not affect far away things. But as soon as we start oscillating that same electron, far away things are now affected?
Electromagnetic waves are a type of energy that does not require a medium to travel through. This means that they can travel through the vacuum of space without losing energy. As long as there is no interference or absorption, electromagnetic waves can maintain their energy indefinitely.
The maintenance of energy in electromagnetic waves is primarily due to their nature as transverse waves. This means that the electric and magnetic fields oscillate perpendicular to the direction of propagation, allowing the energy to remain constant as it travels.
In theory, there is no limit to the distance that electromagnetic waves can travel without losing energy. However, in reality, factors such as interference, absorption, and scattering can cause the energy of EM waves to decrease over long distances.
Unlike mechanical waves, such as sound waves, which require a medium to travel through and can lose energy due to friction and other factors, electromagnetic waves do not require a medium and can maintain their energy over long distances. This is because they do not rely on particles to transfer energy.
Yes, the ability of electromagnetic waves to maintain their energy over long distances is crucial for many modern technologies, including communication systems, satellite transmissions, and wireless energy transfer. Without this property, these technologies would not be possible.