Understanding the electric field

  • #1
adjurovich
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I’ve been trying to get the proper understanding of electric field. Fine I get the definition: any charge changes space around itself and thus generates electric field that acts with force on any object that’s relatively close to the charge.
But first from the first, how can the FIELD act with force, shouldn’t the charge do so? Or is it just the other way to say that charge acts with force?

However, I thought about some example in the case of positive charge: what if we imagine positive charge being some object and electric field acting on test charge like dozens of springs. As the charge tries to get closer, the springs contract more and it gets harder for test charge to come closer so it gets repelled at one point.

For the case of attraction I haven’t made any creative examples yet.

What bothers me the most ie visualizing what is actually happening. It feels quite abstract to imagine charge acting with force that’s being transferred through space. Theoretically I’m fine with that
 
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  • #2
adjurovich said:
For the case of attraction I haven’t made any creative examples yet.
How have you explained to yourself gravity? It is an attractive force mediated by a field in which you have lived all your life which is described by an inverse square law as well.
 
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  • #3
What bothers me is relationship between force and field. Mathematically speaking and theoretically speaking it makes sense to me. But I simply can’t visualize. In textbooks it’s usually said that field acts with force on the charge. Does that mean that the field exerts the force on the charge (test charge)? If so, why do we say Coulomb’s force is attractive or repulsive (dependent on the case) force that acts between two charges? Shouldn’t the charge act with the force on test charge rather than electric field

Edit: the only thing that comes to my mind is that charge “changes” the space around itself and thus this changed space acts with force on the test charge
 
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  • #4
adjurovich said:
What bothers me is relationship between force and field. Mathematically speaking and theoretically speaking it makes sense to me. But I simply can’t visualize. In textbooks it’s usually said that field acts with force on the charge. Does that mean that the field exerts the force on the charge (test charge)? If so, why do we say Coulomb’s force is attractive or repulsive (dependent on the case) force that acts between two charges? Shouldn’t the charge act with the force on test charge rather than electric field

Edit: the only thing that comes to my mind is that charge “changes” the space around itself and thus this changed space acts with force on the test charge
I'm not sure that the concept of an electric field actually makes physical sense. It works as a mathematical model, but if you dig too deeply it's not easy to construct a picture of what is going on. For example, the electric field is maintained even through an intervening charge or mass.

Newton's law of gravity has a similar issue. And, in fact, it was Newton himself who first pointed this out. He was very critical of the physical impossibility of his own theory.
 
  • #5
adjurovich said:
But first from the first, how can the FIELD act with force, shouldn’t the charge do so?
Everything is fields. An electron is a field, a photon is a field, a proton is a bunch of different fields.

So why shouldn’t fields act with forces? Since everything is fields, what else would act with a force?
 
  • #6
adjurovich said:
But first from the first, how can the FIELD act with force, shouldn’t the charge do so? Or is it just the other way to say that charge acts with force?
It's easy to handwave away the field and just say that charges are attracted or repelled from other charges. In a static or nearly static situation that's a fine explanation and there's not a huge need to come up with the concept of the field being a 'real thing'. But we start to run into problems when we get into highly dynamic situations of moving and accelerating charges, where we have to take into account the time delay between a charge being accelerated and a reaction some time later on a different charge.

For example, if I quickly pulse a current through a long metal rod I will find that some time later a nearby metal rod will have an induced current and voltage. Why is there a time delay? What is applying a force to the 2nd rod long after the 1st has lost all its current?

If an electron is placed in a field such that it would undergo circular motion in that field, why is it that the electron (or other charged particle) actually follows a spiral path, gradually moving inwards? Where has its momentum and energy gone? What is applying the force that causes the electron to lose this energy and momentum and thus spiral inwards?

Situations like this are why the field is often considered 'real' by scientists. If it's not real we have some sticky problems that can't really be solved, like energy and momentum temporarily disappearing between the emission and absorption of an EM wave.
 
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  • #7
Dale said:
Everything is fields. An electron is a field, a photon is a field, a proton is a bunch of different fields.

So why shouldn’t fields act with forces? Since everything is fields, what else would act with a force?
Thanks for reply. I would ask one more relatively simple question: could it be considered that after the charge changes space around itself, that changed space (field) attracts or repels other charges to/from its source with Coulomb’s force
 
  • #8
adjurovich said:
Thanks for reply. I would ask one more relatively simple question: could it be considered that after the charge changes space around itself, that changed space (field) attracts or repels other charges to/from its source with Coulomb’s force
I am not sure I agree with calling a field “changed space”. I still have to think on that some more. So I cannot at this time answer the question as written. I tend to not like introducing non-standard terminology for no clear benefit.

However, I can answer this one:

Does the EM field attract or repel charges with Coulomb’s force?

Yes, for a static configuration of charges.

And I can answer this one:

Does the charge act as a source of the EM field?

Yes
 
  • #9
The latter meant more to me. In textbooks we use in high school, they usually define fields as “changed space”. So can it be said that electric field is the source of Coulomb’s force acting on some external charge brought into that field and the charge is the cause of electric field
 
  • #10
I sense this thread is going to go down the rabbit hole of "What is it really?" "But what is it really really?' "But what is it actually really really?"

Physics is not about "truth". It's about creating models that match the real world. If that's not enough, you need a philosopher, not a physicist (but it's likely you will not be satisfied there either).
 
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  • #11
adjurovich said:
they usually define fields as “changed space”
Do you have a reference for that? I have never seen such a definition.

adjurovich said:
So can it be said that electric field is the source of Coulomb’s force acting on some external charge brought into that field and the charge is the cause of electric field
Yes. At the level of Coulomb's law it is a little premature. However, when you get to electromagnetism then you will be introduced to Maxwell's equations and the Lorenz force law as the basis of classical EM. From Maxwell's equations you can derive the retarded potentials: $$\phi (\vec r,t)=\frac{1}{4 \pi \epsilon_0} \int \frac{\rho(\vec r' , t_r)}{|\vec r - \vec r'|}d^3 \vec r'$$$$\vec A(\vec r, t)=\frac{\mu_0}{4\pi}\int \frac{\vec J(\vec r',t_r)}{|\vec r-\vec r'|}d^3\vec r'$$ where $$t_r=t-\frac{|\vec r-\vec r'|}{c}$$

These equations say that the charge density and current density cause the EM field. They are in the right form for a causal relationship since the fields at any time, ##t##, depend on the charge density and current density at the retarded time, ##t_r##, which is always earlier than ##t##. Causes always come before effects.
 
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  • #12
My questions are concerned about the correct way to describe it and understand the description. This is high school level physics and cannot be compared to string theory or some other highly abstract topic. I am not asking for proof but for help to get better understanding of basics. The concept of memorizing dozens of definitions and spitting them out without knowing what they mean to the core is not science at all. I could spit out textbook definitions and get a good grade but what means to me is proper understanding. I didn’t question any of the facts? I questioned my personal understanding and if it aligns with facts checked by experiments and proved mathematically
 
  • #13
adjurovich said:
I am not asking for proof but for help to get better understanding of basics.
The basic point here is that the EM field exerts forces, and charges (and currents) are the source of that field.

In your OP you seem to be trying to dispense with the concept of fields. You cannot do that if you wish to proceed. You need to embrace the concept of fields, not avoid it. This is the most important help we can offer you here.
 
  • #14
... in addition, don't underestimate the importance of mathematics on the road to understanding. In advanced physics, the mathematics is often the key to retraining your intuition.
 
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  • #15
Dale said:
The basic point here is that the EM field exerts forces, and charges (and currents) are the source of that field.

In your OP you seem to be trying to dispense with the concept of fields. You cannot do that if you wish to proceed. You need to embrace the concept of fields, not avoid it. This is the most important help we can offer you here.
Now it does make sense to me. I usually start a post by explaining my understanding and the things that don’t make sense in my understanding. So I ask what I got wrong. I don’t even want to go deeper because I am not yet mathematically capable as a high school student and I usually avoid questioning physics (I am not even close to being capable to do so). I question my understanding of physics. Maybe I haven’t composed the post correctly… I am still new here
 
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  • #16
PeroK said:
... in addition, don't underestimate the importance of mathematics on the road to understanding. In advanced physics, the mathematics is often the key to retraining your intuition.
My knowledge of mathematics is pretty good for my age (speaking of results I achieve compared to my peers), but it’s very far from being sufficient for me to dig deeper into intermediate physics as I can understand only the basics of calculus I self-taught myself. I don’t avoid it (I am sometimes probably too much relying on math sometimes so that’s why I ask theoretical questions), as long as it’s not several years ahead of my level of education (for example, Maxwell’s equations)
 
  • #17
adjurovich said:
My questions are concerned about the correct way to describe it and understand the description.
It's not complicated. Charges create an electric field around themselves that then exerts a force on other charges. Exactly how everything works in detail is given by the relevant equations.

adjurovich said:
The concept of memorizing dozens of definitions and spitting them out without knowing what they mean to the core is not science at all.
I'd expect a physicist to understand these concepts 'to the core', but not a high school student. That takes time and work. If you can do your homework and test problems correctly and have a fairly good understanding of everything going on in these problems then you are doing just fine. It's okay to still feel like you're not understanding something deeper. Your knowledge of physics is still incomplete and the stuff you do know is still new to you.
 
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