Can an electric field change faster than light?

In summary: Maxwell's equations state that an electric field can create a magnetic field, and vice versa. Thus, an EM wave is created. Maxwell's equations also show that an electric field can't change faster than light, because light is the information that the electric and magnetic field has changed.
  • #1
Meizirkki
55
0
I found the thread "Can magnetic field expand faster than light?" but no thread on electric fields.

For example:

iBiOU.png


If, in the above setup, the dielectrics used in capacitors were physically very long (the distance between plates very high) and the capacitors were charged up to high potential in a way that closing the switch would create a HV peak measurable at the resistor, is it possible that this peak could appear faster than light travels the distance between capacitor plates?
 
Physics news on Phys.org
  • #2
Light consists of electric and magnetic fields so the speed of light is hardly likely to be different. April 1st was several days ago.
 
  • #3
sophiecentaur said:
Light consists of electric and magnetic fields so the speed of light is hardly likely to be different. April 1st was several days ago.

This thread is not an april fools joke.

In a capacitor, nothing has to travel the distance between the plates (and nothing does, assuming a perfect dielectric). Is there a reason why the speed of light would be a limit?
 
  • #4
Electric fields and magnetic fields are both electromagnetic fields.
Both expand at most as fast as the speed of light in vacuum.
 
  • #5
An EM wave consists of changing E and H fields. The rate of propagation of a change in field IS the speed of the EM wave. How could it be different?
Why are people obsessed with the dielectric in a capacitor? Capacitors can have a vacuum between the plates. Any material between will SLOW DOWN the wave speed - that's what the refractive index is about.
 
  • #6
Excuse my ignorance. I just don't quite understand this. And all this EM wave talk is making it much more confusing. There's no EM wave in a capacitor, right?

I can understand this very well for magnetic field that starts from one point and expands, but electric field lies on the sides of the dielectric and does not propagate through it. If the charge is changing on one side.. it has to change on the other side too? Otherwise the field can be canceled out and that wouldn't make any sense either.

Do I just lack knowledge of time to understand this?
 
  • #7
Meizirkki said:
Excuse my ignorance. I just don't quite understand this. And all this EM wave talk is making it much more confusing. There's no EM wave in a capacitor, right?

I can understand this very well for magnetic field that starts from one point and expands, but electric field lies on the sides of the dielectric and does not propagate through it. If the charge is changing on one side.. it has to change on the other side too?
Do I just lack knowledge of time to understand this?

Ever hear of Maxwell's equations?
A changing electric field produces a magnetic field, and vice versa. Ergo, an EM "wave".

"Equation Four" here ought to suffice...
http://www.google.com/imgres?imgurl...a=X&ei=1vmAT6XhAdGhtwec192TBg&ved=0CCwQ9QEwBA
Read through from "Equation Four" to the bottom (last two eqns. are for the resultant EM wave.)
Simplistic, but you will get the idea.

Creator
 
Last edited:
  • #8
A charged particle does not know it has to move differently unless the force on it changes, i.e. the electric field changes. Light in itself is the information that the electric and magnetic field has changed. When you wiggle an atom back and forth, the force felt by a stationary particle some distance away changes, because of the inverse square law. When the electric field changes, it creates a wavefront traveling at the speed of light with the information of a changed electric (and magnetic) field and that is what light is. Electrons do not know what the charge is on the other plate or anything else, they just act once the information about the changed field reaches them and that's what light is.

So an electric field cannot change faster than light, because light is how a particle knows the field has changed.
 
  • #9
It may help to think of the scale involved. The separation between capacitor plates is very small, compared with the wavelength of typical RF signals so you can't think of 'whole wavelengths' between them. The voltage on one plate will lag behind that on the other plate but this lag represents only a small portion of an actual wave.
 
  • #10
Thank you for the replies.
 
  • #11
While the fields can't change faster than light, Maxwell's equations does show a parameter that can be FTL and can be used to generate EM waves of a curious nature.

http://oxbridgepulsars.moonfruit.com/
 
  • #12
the reason that light (at whatever frequency) propagates at this apparently constant speed (we call "c") is because the electromagnetic interaction propagates at that speed.

it is a fundamental property of nature that these ostensibly "instantaneous" fundamental forces all propagate at this speed which is sometimes called the "speed limit" of the universe.
 
  • #13
rbj said:
the reason that light (at whatever frequency) propagates at this apparently constant speed (we call "c") is because the electromagnetic interaction propagates at that speed.

it is a fundamental property of nature that these ostensibly "instantaneous" fundamental forces all propagate at this speed which is sometimes called the "speed limit" of the universe.

I'm supposing this includes gravity, too?

Does the observation that it acts at the speed of "c" (but does it?) constitute good evidence that gravity is also, at root, an electromagnetic interaction?

Respectfully submitted,
Steve
 
  • #14
Dotini said:
I'm supposing this includes gravity, too?

Does the observation that it acts at the speed of "c" (but does it?) constitute good evidence that gravity is also, at root, an electromagnetic interaction?

Respectfully submitted,
Steve

Yes, changes in gravity also expand at the speed of light.
But disappointingly gravity really is not an electromagnetic interaction.
(We're still waiting for the grand unification theory.)
 
  • #15
I like Serena said:
Yes, changes in gravity also expand at the speed of light.
But disappointingly gravity really is not an electromagnetic interaction.
(We're still waiting for the grand unification theory.)
Why are you "disappointed" about this? It's something we are 'stuck with' just the same as the length of a day and taxes. I guess that, somewhere along the line, when a Unified Theory arrives, it will take us somewhere beyond this and possibly suggest applications where the commonality can be made use of - possibly for FTL, antigrav etc.
 

1. Can an electric field travel faster than the speed of light?

No, according to the theory of relativity, the speed of light is the fastest possible speed in the universe. This means that nothing, including an electric field, can travel faster than the speed of light.

2. Can an electric field be created and change faster than the speed of light?

No, the creation and change of an electric field are governed by electromagnetic waves, which also travel at the speed of light. Therefore, the electric field cannot be created or changed faster than the speed of light.

3. Is it possible for an electric field to affect objects faster than the speed of light?

No, an electric field can only affect objects within its range at the speed of light. This is because the electric field is a type of force that is transmitted through electromagnetic waves, which travel at the speed of light.

4. Can an electric field be faster than light in a vacuum?

No, the speed of light in a vacuum is a fundamental constant of the universe. This means that even in a vacuum, an electric field cannot travel or change faster than the speed of light.

5. Is there any evidence of an electric field traveling faster than light?

No, there is no evidence to suggest that an electric field can travel faster than the speed of light. In fact, numerous experiments and observations have consistently shown that the speed of light is the maximum speed in the universe.

Similar threads

Replies
4
Views
937
  • Electromagnetism
Replies
18
Views
1K
Replies
14
Views
964
Replies
3
Views
378
Replies
61
Views
2K
Replies
12
Views
985
Replies
7
Views
1K
Replies
7
Views
17K
  • Electromagnetism
Replies
2
Views
837
Replies
2
Views
2K
Back
Top