Ampere's Law: Explained and the Role of Magnetic and Electric Fields

In summary, the conversation discusses the concept of ampere's law and its relation to the magnetic field around a wire carrying current. The right hand rule is mentioned as a convention chosen to explain the observed forces between current-carrying wires and moving charges. The question of why charge in motion causes a magnetic field is also brought up. The conversation also touches on the possibility of different geometric configurations for the magnetic field and the use of scientific method in understanding magnetism. Finally, the idea of a preferred direction in space and its implication on the concept of absolute frame of reference is mentioned.
  • #1
physics user1
I know the ampere's law but I want an explanation on why it exist in that way, consider a wire where flows current, i know that when an observer is in relative motion to the current there is a magnetic field but why in this geometric configuration and not in another? What about the electric field outside? I guess is zero unless we don't move at the same velocity on the current so that our frame of reference is solidal with it, then the electromagnetic field is just electric field, is that TRUE? I mean, if we see current flowing all the field is magnetic, if we don't see current all the field is going to be electric due to Lorentz contraction law and all that stuff right?
Why the magnetic field outside a wire obeys to the right hand rule?
 
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  • #2
Can you focus your question down to one most important key question? You have so many scattered questions that you will get scattered responses.
 
  • #3
Dale said:
Can you focus your question down to one most important key question? You have so many scattered questions that you will get scattered responses.

Why does the magnetic field outside the wire carrying current obey to the right hand rule, why does it formes circumferences around the wire?
 
  • #4
That is just a convention. We could have chosen a left handed convention and all of the physics would have worked out the same.
 
  • #5
We don't observe the magnetic field directly. Instead we observe the forces between current-carrying wires and moving charges. Our rules for the direction of the magnetic field produced by a current (or moving charge), and the force exerted by a magnetic field on a current (or moving charge) were chosen so as to accommodate our observations of the forces between currents and moving charges moving at various angles with respect to each other.

As Dale noted, we could use a "left-hand rule" for the magnetic field if we also used a matching "left-hand rule" for the magnetic force exerted by that field. Mathematically, this would be equivalent to putting minus signs in the two equations, which would cancel out when we combine them.
 
  • #6
Cozma Alex said:
Why does the magnetic field outside the wire carrying current obey to the right hand rule, why does it formes circumferences around the wire?

Back up a step - why does charge in motion cause a magnetic field at all ?
 
  • #7
P
jim hardy said:
Back up a step - why does charge in motion cause a magnetic field at all ?
Is a relativistic effect
 
  • #8
Cozma Alex said:
Is a relativistic effect

an observed trait of the universe

What if it'd been hexagonal instead of circular ? The formulas would be a little different, that's all..
 
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  • #9
jim hardy said:
an observed trait of the universe

What if it'd been hexagonal instead of circular ? The formulas would be a little different, that's all..

So... it's like that because the universe is made this way
 
  • #10
jim hardy said:
What if it'd been hexagonal instead of circular ?
That would imply a very arbitrary case of symmetry. If it had to be a hexagon pattern, would the sides of hexagons for different wires all be parallel from wire to wire? It would imply 'preferred' directions in space which would be very unsatisfactory for Mathematicians, if nothing else (lol). The circle is the least arbitrary pattern in this case. Geometry is a pretty powerful argument here, as it is when you justify the Inverse Square Law.
 
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  • #11
Cozma Alex said:
So... it's like that because the universe is made this way
I think so.

Place iron filings around a wire and observe the pattern.
magneticfieldsaroundcurrents3.JPG

Then figure out what math describes it.
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/biosav.html
upload_2016-7-22_16-31-15.png
Scientific method:
Observe something.
Then figure out what math explains the observations.
Then see if the math ever fails, and when it does adjust it.

Isn't that how relativity came about ?

I think if i understood what magnetism really is i'd have a nice lab at Princeton.

old jim
 
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  • #12
sophiecentaur said:
It would imply 'preferred' directions in space which would be very unsatisfactory for Mathematicians,

hmmmm would preferred directions infer that dreaded "absolute frame of reference" ?
 

1. What is Ampere's Law and how does it relate to electricity and magnetism?

Ampere's Law is a fundamental principle in electromagnetism that describes the relationship between magnetic fields and electric currents. It states that the magnetic field created by a closed loop of electric current is directly proportional to the electric current passing through the loop. This law is important for understanding the behavior of electric currents and magnetic fields in various systems, including motors, generators, and transformers.

2. What is the role of magnetic fields in Ampere's Law?

Magnetic fields play a crucial role in Ampere's Law, as they are responsible for the creation of the magnetic force that acts on electric currents. According to the law, the strength of the magnetic field is directly proportional to the electric current, which means that a stronger current will produce a stronger magnetic field.

3. How does Ampere's Law explain the behavior of electric currents?

Ampere's Law explains the behavior of electric currents by stating that the magnetic field created by a current is always perpendicular to the current. This means that the magnetic force acts at a right angle to the direction of the current, causing the current to move in a circular path. This principle is used to understand the behavior of electric currents in various devices, such as solenoids and electric motors.

4. Can Ampere's Law be applied to non-closed loops of electric current?

No, Ampere's Law only applies to closed loops of electric current. This is because the law is based on the principle of conservation of energy, which states that the total energy in a closed system remains constant. Therefore, the law cannot be applied to non-closed loops, as energy may enter or leave the system through open ends.

5. What is the significance of Ampere's Law in the study of electromagnetism?

Ampere's Law is significant in the study of electromagnetism because it provides a mathematical relationship between electric currents and magnetic fields. This allows scientists and engineers to predict and control the behavior of electric currents and magnetic fields in various systems. It also forms the basis for many other important laws and principles in electromagnetism, such as Faraday's Law and Maxwell's equations.

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