1)2 protons move parallel to each other with equal speeds of 3 x 10^5 m/sec. what is the ratio of magnetic and electrical forces between them?
The electrical forces exist between 2 charged particles when they are stationary. Will there be electrical force between 2 moving charged particles? Moreover, in order to calculate the magnetic force between them, the magnetic field produced by the proton should be known. How to find that? Can someone give an idea to solve it?

you have missed one important factor. they are moving parallel right? (same direction?) not anti-parallel? also they have the same speed with respect to some outside observer. what would one of the protons see as the others velocity?

also, you know the charge (+e) but not distance, so the answer must be symbolic, and not a numerical expression, as radius should matter.

you have missed one important factor. they are moving parallel right? (same direction?) not anti-parallel? also they have the same speed with respect to some outside observer. what would one of the protons see as the others velocity?

velocity of one proton as observed by the other would be zero. But how to go further?

I'm not sure you can go farther. If we imagine a universe in which these two protons are the only two objects, then it would be impossible to know they are moving at any speed. Therefore they might as well be moving at 0 speed (since relative to each other, they are). I think the only forces that would come into play would be the repulsive electric force between the two.

-AntonK

velocity of one proton as observed by the other would be zero. But how to go further?

for a qualitative answer you should do the following:
let us clla the two protons a and b.
In the rest frame of the two protons, let us look at the electric field created by proton a. It is just the usual electric field generated by a stationary charge and it is given by E = ke/r^2 (with radial direction). So that the electric force acting on proton B is given by eE.
Let us see what is happening in a frame where both protons move with velocity v. proton a generates an electric field E' (that you don't know yet) which is the electric field generated by a moving charge. But since it is moving, it is also an electric current. This electric current generates a magnetic field that you can in principle calculate using for example Bio-Savart Law. Proton b is now an electric charge moving in a magnetic field B generated by proton a and in an electric field E' also generated by proton a. So that there will be a force acting on it which has two parts:
F (on b) = F(el) + F(magn) = eE' + ev x B (here x stands for the vector product). Since the difference between the two frame is by a constant velocity, the accelerations in both frames are the same and so are the forces acting on proton b. so that you can write that eE = eE' + ev x B.
From there you can find E'.
In fact, what you get here is that the magnetic and electric fields are not two diffrent entities but two parts of the same entity: the electromagnetic field. and what you see in one frame as an electric field, is seen in another frame as an electric field and a magnetic field.
I suggest you to do the same exercise , instead of point charges (the two protons) with two infinite linear charges. since the meagnetic field and electric fields are easilly found (using Ampere law and Gauss law).

Finaly, if you want to find the exact transformations, you should use the Lorentz transformation, where the electromagnetic field is a tensor of rank two, and transforms frrom one frame to another acocordingly.

If both of the protons are moving at the same speed, parallel, as it has been said, they are not really moving at all relative to each other.
So, if the interactions between them are somehow different because they are moving relative to an observer, than if they were stationary relative to the same observer, it would be quite a paradox?

1)2 protons move parallel to each other with equal speeds of 3 x 10^5 m/sec. what is the ratio of magnetic and electrical forces between them?
The electrical forces exist between 2 charged particles when they are stationary. Will there be electrical force between 2 moving charged particles? Moreover, in order to calculate the magnetic force between them, the magnetic field produced by the proton should be known. How to find that? Can someone give an idea to solve it?

Well then let's see what we have here.

Many years ago today ( metaphorically ) Ampere discovered that two conductors, such as two wires, arranged parallel and carrying currents ( sometimes known as moving charges ) in the same direction, produced a discernable magnetic attraction, relative to observers who were stationary with respect to the conductors but who were participating in relative velocity with respect to the current. This has been an alledged phenomena which has gained such a cult following that the exact simple science experiment has become the official definition of the Ampere ( the measurement of electric current ).

Critics of the concept have claimed that the Coulomb electric field repulsion between charges will not become equal to the induced magnetic field attraction until the charges are moving at a velocity of c with respect to the observer, implying that net attraction would only happen at a velocity beyond c.

Any physics textbook, such as the ubiquitous Serway's, has a clearly and completely explained description and mathematical analysis of the alledged magnetic attraction between moving charges moving in the same direction and also between charges moving in opposing directions, and also between opposite charges having relative motion.

If it is your lucky day, you might be able to find a physics textbook in your nearest public library, college library, or college bookstore.

If both of the protons are moving at the same speed, parallel, as it has been said, they are not really moving at all relative to each other.
So, if the interactions between them are somehow different because they are moving relative to an observer, than if they were stationary relative to the same observer, it would be quite a paradox?

A Relativity paradox? Is there really such a thing? Aren't they like unicorns?

Well then let's see what we have here.

Many years ago today ( metaphorically ) Ampere discovered that two conductors, such as two wires, arranged parallel and carrying currents ( sometimes known as moving charges ) in the same direction, produced a discernable magnetic attraction, relative to observers who were stationary with respect to the conductors but who were participating in relative velocity with respect to the current. This has been an alledged phenomena which has gained such a cult following that the exact simple science experiment has become the official definition of the Ampere ( the measurement of electric current ).

Critics of the concept have claimed that the Coulomb electric field repulsion between charges will not become equal to the induced magnetic field attraction until the charges are moving at a velocity of c with respect to the observer, implying that net attraction would only happen at a velocity beyond c.

Any physics textbook, such as the ubiquitous Serway's, has a clearly and completely explained description and mathematical analysis of the alledged magnetic attraction between moving charges moving in the same direction and also between charges moving in opposing directions, and also between opposite charges having relative motion.

If it is your lucky day, you might be able to find a physics textbook in your nearest public library, college library, or college bookstore.



The sum of electric charges of protons and electrons in each wire should roughly sum up to zero even though the electrons are "moving" - their number has not increased relative to proton numbers. This leaves only the magnetic field induced by electron movement. The protons are NOT moving(compared to electrons) so they do not "counter" the magnetic field of moving electrons.
So, in the end we only have the magnetic fields of the two wires as "the cult" proposes.

Am I missing something here, or are these "Critics of the concept" being a bit thick?

The sum of electric charges of protons and electrons in each wire should roughly sum up to zero even though the electrons are "moving" - their number has not increased relative to proton numbers. This leaves only the magnetic field induced by electron movement. The protons are NOT moving(compared to electrons) so they do not "counter" the magnetic field of moving electrons.
So, in the end we only have the magnetic fields of the two wires as "the cult" proposes.

Am I missing something here, or are these "Critics of the concept" being a bit thick?


You are apparently missing reading and understanding the reference given to you.

If you look at the force between two current-carrying wires, it is solely magnetic when viewed in the "laboratory" reference frame. The electric forces from the protons and electrons in each wire cancel each other out, so there is no net electric attraction or repulsion in this frame. That only leaves the magnetic force due to the electron motion, which is an attractive force for parallel currents.

If we instead look at things in the frame of the moving electrons, then we see something different. There is now no magnetic force between electrons in the two wires, since their speed relative to one another is zero. However, there is now an attractive magnetic force between the protons in the wires, which are moving. There is also an electric force between the wires, because the linear charge density of electrons is no longer the same as the linear charge density of protons, due to relativistic length contraction.

The relationship between electricity and magnetism is well understood, and comes from the theory of relativity. That's why we now refer to electric and magnetic forces as two different aspects of a single force known as electromagnetism.

Hmm, Last time I checked you have to apply a difference in electrical potential to get current (electrons/holes) to move in a wire. This potential sets up a field that realigns the electrons so that the electrons' magnetic moments (due to electron spin) align/sum to produce an external (to the wire) magnetic field. The electrons do move through the wire and generate heat from electric field interaction/collision with the atoms in the wire. The speed of the electron is nowhere near the speed that the potential field travels through the wire.
:)

Hmm, Last time I checked you have to apply a difference in electrical potential to get current (electrons/holes) to move in a wire. This potential sets up a field that realigns the electrons so that the electrons' magnetic moments (due to electron spin) align/sum to produce an external (to the wire) magnetic field. The electrons do move through the wire and generate heat from electric field interaction/collision with the atoms in the wire. The speed of the electron is nowhere near the speed that the potential field travels through the wire.
:)

In the electron gas concept of conductors, a quantity of electrons approximately equal to the number of atoms in the conductor are in motion between ionized matrix atoms at any given moment. This is the normal condition in the absence of an electric field potential. The free electrons in the electron gas are moving in random directions so that the average velocity of all the electrons is zero even though the individual velocities are significantly high, though far below the velocity of the electric wave when such is present.

In a simple table top science experiment which could easily be put together for materials costing little at *adio *hack, the phenomena of Ampere attraction between parallel conductors can be demonstrated in which the average free electron velocity, called in such a case the drift velocity, is, due to weakness of the electric wave and very low necessary current, is somewhat less than one foot per hour.

No typo: ONE FOOT PER HOUR.

In ordinary electromechanical devices, such as electric drills, power saws, sink garbage disposals, and others which can almost apparently instantaneously provide an experimenter with extreme bodily harm, the electron drift velocity executing powerful magnetic attraction or repulsion between parallel conductors is not much more: something like ONE YARD PER HOUR.

This is all very basic physics, easily found and clearly explained in any college physics textbook printed in a hundred years.

O, Lorentz contraction, O Special Relativity contraction, where is thy sting?

What you've just written seems to be irrelevant to the discussion, CANGAS.

Montec:

The magnetic field produced by electric current in a wire has nothing to do with spin alignments. It is solely an effect due to moving charge.

Hi James R
The magnetic field produced by current in a wire is based on the number of charge carriers (electrons) in the wire and not just by their velocity (which is limited). The magnetic field strength in a bar magnet is based in part on the number of unpaired electrons, with the same spin, held by the atoms of the magnet. The electron is the same in both cases. There is a simularity here. The EMF produced by a changing magnetic field is also related to the spin (magnetic moment) of the electron (magnets tend to line up to an applied magnetic field). And lets not forget plasmonds (field waves in electrons on the surface of conductors).
:)

CANGAS, I agree with James R, what is your point?

What you've just written seems to be irrelevant to the discussion, CANGAS.

It no longer surprises me when you don't understand the relevance of something, JAMESR.

CANGAS, you simply state something that is widely known, that drift velocity is normally quite low and then from that jump to make remarks about relativistic theory?

Is that because James R said that understanding of electromagnetism comes from relativistic theory?

CANGAS, I agree with James R, what is your point?

You must forgive me for not being clairvoyant. The fact is, I do not understand the point of your asking me about what is my point. Are you trying to initiate some weird kind of game in which we are expected to guess the point of the other's post?

If you don't understand the point, you just don't understand it. If JR doesn't understand physics, he just doesn't understand physics. If you don't understand physics, you just don't understand physics.

No problem. I sure don't really care if either of you understand physics now or in the future.

Whatever.

Montec:

The magnetic field produced by current in a wire is based on the number of charge carriers (electrons) in the wire and not just by their velocity (which is limited).

The field depends on the electric current, which is, in turn, equal to the net amount of charge passing a point in the wire per second. That quantum does indeed depend on the density of charge carriers as well as their velocity and their charge.

The magnetic field strength in a bar magnet is based in part on the number of unpaired electrons, with the same spin, held by the atoms of the magnet.

Ok...

The electron is the same in both cases. There is a simularity here. The EMF produced by a changing magnetic field is also related to the spin (magnetic moment) of the electron (magnets tend to line up to an applied magnetic field). And lets not forget plasmonds (field waves in electrons on the surface of conductors).

I don't see how this affects what I said previously - that the magnetic field around a wire is not due to electron spin, but simply due to charge flow in the wire.

Do you agree with me?

Hi James R
The speed at which the electrons move in the wire is limited by the metal lattice of the wire. An individual electron moves only a small distance while the magnetic and electric fields of the electron travel at near the speed of light. Current flow in a wire travels at near the speed of light.The applied EMF causes an electron chain reaction in the electron cloud of the metal. Each electron's electric/magnetic field causes the next electron's electric/magnetic field to rotate into alignment. The charge flow results in the spin alignment of the electrons. Hence each electron's magnetic moment are summed to generate the magnetic field This is how I understand the mechanism behind the generation of magnetic fields from current flow.

If you can explain how an electron moving relative to a metal ion can generate a magnetic field and how the flow of current travels at near the speed of light while the electron is nearly at a standstill in comparison then I am all ears.
:)

Montec:

The speed at which the electrons move in the wire is limited by the metal lattice of the wire. An individual electron moves only a small distance while the magnetic and electric fields of the electron travel at near the speed of light.

Specifically, the drift velocity is related to the current density by:

J = nqv

where n is the density of charge carriers, q is the charge on each one and v is the drift velocity.

Current flow in a wire travels at near the speed of light.

I'm not sure what you mean by this. Current is a measure of the amount of charge passing a point per unit time. It is not a "substance" that can travel.

The applied EMF causes an electron chain reaction in the electron cloud of the metal. Each electron's electric/magnetic field causes the next electron's electric/magnetic field to rotate into alignment.

No.

Notice that an applied EMF is related only to the electric field. An applied EMF has no magnetic effects in and of itself.

The charge flow results in the spin alignment of the electrons.

No, I don't think so. Where did you get this idea? References?

Hence each electron's magnetic moment are summed to generate the magnetic field This is how I understand the mechanism behind the generation of magnetic fields from current flow.

This is wrong, as I've already stated. The magnetic field is due to the moving charge and has nothing to do with spin alignments.

If you can explain how an electron moving relative to a metal ion can generate a magnetic field and how the flow of current travels at near the speed of light while the electron is nearly at a standstill in comparison then I am all ears.

All moving charges generate magnetic fields. That's the basic mechanism behind magnetic fields.

I agree that electrons in a wire do not move at anywhere near the speed of light. I agree that an applied potential difference produces a constant electric field inside the wire at almost the speed of light. That, in turn, causes electrons to move, and it is that motion which produces the magnetic field.

If you think I am wrong, please try to produce some kind of reference for your idea. Otherwise, I fear we'll just go round and round in circles.

The electric wave in the "average" conductor travels at about 2/3 the speed of light in vacuum; this is very widely published and agreed upon in science literature.

The free electron speed of free electrons in conductors in the absence of an electric wave is rather high, but nowhere near the speed of light.

When an electric wave is present in a conductor, the free electrons are persuaded to accelerate. However, in circumstances germain to normal human experience, such as the circumstances in a wire in your house when you turn on your light, the increased velocity is truly puny. The INCREASED electron velocity in such a circumstance is as small as the velocity of a very, very lazy snail. A snail that could run at 1 mile per hour would outrun the drift velocity of such electrons by an Olympic margin.