Can a magnetic fields/forces do work on a current carrying wire?

[Miyz]

I'm just confused...

I know that magnetic fields can do work only on pure magnetic dipoles like a bar magnet. Based on the formula, the magnetic force on a charge is qv⃗ ×B⃗ which is identically perpendicular to v⃗ and that's why it does no work. However, forces on magnetic dipoles and more general objects don't have the form v⃗ × - they're not perpendicular to v⃗ , so they do work in general.

But still when I look at this picture I get confused:

http://ecommunity.pwsd76.ab.ca/file.php/1030/moddata/resource/23766/physics_30/images/m4/103_dc_motor.jpg

In this picture aren't magnetic force causing the rotation of the loop! Aren't the magnetic forces in a motor on of the key! Factors of motion within it? I mean it makes no sense to me why in this cause magnetic force can't do work on an electric charge... Could someone pelase help me out with this!

 

[Miyz]

The only explanation that can come to my mind is... The electric charge creates a magnetic field and the permanent magnet has already a magnetic filed and thus opposing forces will be apply forces and work will be done by both the electric charged and the magnetic fileld.

As stated by Lorentz law on a current carrying wire: F = IL x B , B = 0 , F = 0 , total work done would equal = zero, simple logic about this matter if you make a small loop and connect it to a battery nothing would happen other then flow of current and a magnetic field is generated by that flow, put a permanent magnet into that state and voila! Motion!

 

[Darwin123]

I'm just confused...

I know that magnetic fields can do work only on pure magnetic dipoles like a bar magnet. Based on the formula, the magnetic force on a charge is qv⃗ ×B⃗ which is identically perpendicular to v⃗ and that's why it does no work. However, forces on magnetic dipoles and more general objects don't have the form v⃗ × - they're not perpendicular to v⃗ , so they do work in general.

But still when I look at this picture I get confused:

http://ecommunity.pwsd76.ab.ca/file.php/1030/moddata/resource/23766/physics_30/images/m4/103_dc_motor.jpg
In this picture aren't magnetic force causing the rotation of the loop! Aren't the magnetic forces in a motor on of the key! Factors of motion within it? I mean it makes no sense to me why in this cause magnetic force can't do work on an electric charge... Could someone pelase help me out with this!

You did not include the internal forces in the wire. The internal forces that keep the wire together are actually doing all the work. The wire loop is acting like a rigid body. Rigid bodies are held together by internal forces. The internal forces in the wire are doing the work, not the magnetic field of the bar magnet.
The rigid loop is doing work on the commutator. The magnetic field isn't doing work on the commutator. Therefore, the "key" forces are the internal forces of that loop of wire. The internal forces both keep the wire rigid and keep the electric charges that carry the current in the wire.
The magnetic field isn't directly causing the torque. The contact forces between the electric current and the rest of the wire is directly causing the torque.
The wire of the loop has two components. One is the free electrons in the wire. The other is atoms of the wire, including both bound electrons and nuclei.
Think of a single conduction electron in the copper wire. The copper wire is initially still in the laboratory frame. The electron initially moves perpendicular to the magnetic field of the bar magnet. The magnetic field causes a force that is perpendicular to the electrons motion. No work is done by the magnetic field, as you said.
The electron can't leave the copper wire. When the wire gets to the edge of the copper wire, it has to slow down. The edge of the copper wire applies a force to the electron which stops it from jumping into the air. One could describe this as a contact force (i.e., a sharp wall). Or maybe one would prefer to think of it as electrostatic attraction of the electron and the positive ions in the copper wire. In any case, a force is applied to the electron by the edge of the wire that slows the electron down.
For every action, there is a reaction (Newton's third law). When the electron nears the edge of the copper wire, it applies a force on the edge that is equal and opposite the force that the edge applies on the electron. Hence the electron is applying a force to the wire.
The force of the electrons on the wire is what causes the torque. The force is not directly caused by the bar magnet. If the electrons were not bound by the wire, then there would be no work done. However, the wire keeps the electrons in place. The forces that keep the electrons in place are not from the bar magnet. The forces that keep the electrons in place have to be accounted for in some way.
You made an identification between the electric charges, the electric current and the wire. The electric charges carry the current. The electric charges that carry the current are only part of the wire. The rest of the wire is necessary to keep the electrons flowing on the path of the wire. The magnetic field of the bar magnet does no work on the electric charges that make up the current.
When your instructor said that magnetic fields can't do work on the current, he was literally correct. However, he did you a bit of a disservice. This type of rule has to be used with caution. The path of the electric current in a wire is constrained by the shape of the wire. Therefore, the forces that keep the electric current in the wire can't be ignored. Constraints imply forces that aren't always explicit in the wording of the problem.

Lesson for engineers: Always take into account the constraints, because the constraints imply internal forces.
Lesson for physicists: Boundary conditions are always important, especially those caused by constraints.

 

[Miyz]

You did not include the internal forces in the wire. The internal forces that keep the wire together are actually doing all the work. The wire loop is acting like a rigid body. Rigid bodies are held together by internal forces. The internal forces in the wire are doing the work, not the magnetic field of the bar magnet.
The rigid loop is doing work on the commutator. The magnetic field isn't doing work on the commutator. Therefore, the "key" forces are the internal forces of that loop of wire. The internal forces both keep the wire rigid and keep the electric charges that carry the current in the wire.
The magnetic field isn't directly causing the torque. The contact forces between the electric current and the rest of the wire is directly causing the torque.
The wire of the loop has two components. One is the free electrons in the wire. The other is atoms of the wire, including both bound electrons and nuclei.
Think of a single conduction electron in the copper wire. The copper wire is initially still in the laboratory frame. The electron initially moves perpendicular to the magnetic field of the bar magnet. The magnetic field causes a force that is perpendicular to the electrons motion. No work is done by the magnetic field, as you said.
The electron can't leave the copper wire. When the wire gets to the edge of the copper wire, it has to slow down. The edge of the copper wire applies a force to the electron which stops it from jumping into the air. One could describe this as a contact force (i.e., a sharp wall). Or maybe one would prefer to think of it as electrostatic attraction of the electron and the positive ions in the copper wire. In any case, a force is applied to the electron by the edge of the wire that slows the electron down.
For every action, there is a reaction (Newton's third law). When the electron nears the edge of the copper wire, it applies a force on the edge that is equal and opposite the force that the edge applies on the electron. Hence the electron is applying a force to the wire.
The force of the electrons on the wire is what causes the torque. The force is not directly caused by the bar magnet. If the electrons were not bound by the wire, then there would be no work done. However, the wire keeps the electrons in place. The forces that keep the electrons in place are not from the bar magnet. The forces that keep the electrons in place have to be accounted for in some way.
You made an identification between the electric charges, the electric current and the wire. The electric charges carry the current. The electric charges that carry the current are only part of the wire. The rest of the wire is necessary to keep the electrons flowing on the path of the wire. The magnetic field of the bar magnet does no work on the electric charges that make up the current.
When your instructor said that magnetic fields can't do work on the current, he was literally correct. However, he did you a bit of a disservice. This type of rule has to be used with caution. The path of the electric current in a wire is constrained by the shape of the wire. Therefore, the forces that keep the electric current in the wire can't be ignored. Constraints imply forces that aren't always explicit in the wording of the problem.

Lesson for engineers: Always take into account the constraints, because the constraints imply internal forces.
Lesson for physicists: Boundary conditions are always important, especially those caused by constraints.

Ok, I understood that the force within the wire are the main cause of torque and for work being done. I agree. However, what's a bar magnets role in this?

Its presence is crucial! A loop of wire can not generate a "twist" torque. Its the repulsion/attraction of the magnetic field don't you agree?

(Forgive me if I didn't understand you properly but I'm confused and still find the presence and use of bar magnets is crucial for the "motor" effect to occur)

 

[Miyz]

Noticed that this is not a really popular topic around the forums huh?

Also noticed its a very very misunderstood field... Seriously! I looked around here and there... No simple and common answer about this. I can say its not understood properly and strangely everyone is confused from other sites and countless sources... No one really knows what exactly does work in a motor... One would say:"well its electricity?" okay, bring a loop of wire and wait for it to spin... NOTHING happens. Bring a small tiny magnet and all of a sudden its turning so fast! I could say that magnets are doing something and that's repelling/attracting the loop because the flow of current in it! Is generating a magnetic field the loop itself is like a magnet that can attract/repel...

This site makes most sense to me...

 

[cabraham]

https://www.physicsforums.com/showthread.php?t=347539&page=4

The above link is worth reading. Several posters put forth good info. I emphasized the tethering concept which I can elaborate upon if needed.

Claude

 

[truesearch]

'The electron can't leave the copper wire. When the wire gets to the edge of the copper wire, it has to slow down. The edge of the copper wire applies a force to the electron which stops it from jumping into the air. One could describe this as a contact force (i.e., a sharp wall). Or maybe one would prefer to think of it as electrostatic attraction of the electron and the positive ions in the copper wire. In any case, a force is applied to the electron by the edge of the wire that slows the electron down.'
If there is an electrostatic attraction between the electrons and the positive charges then there is no resultant force on the wire. As you say this force is an 'internal' force and cannot be the explanation for any external force causing the wire to move.
I don' think the electron gets to the edge of the wire and has to 'slow down' which stops it 'jumping into the air'
There are several points you should consider.
Have you heard of the 'Hall effect'?
Can you quote a textbook or other reference that backs up you explanation?

 

[cabraham]

You did not include the internal forces in the wire. The internal forces that keep the wire together are actually doing all the work. The wire loop is acting like a rigid body. Rigid bodies are held together by internal forces. The internal forces in the wire are doing the work, not the magnetic field of the bar magnet.
The rigid loop is doing work on the commutator. The magnetic field isn't doing work on the commutator. Therefore, the "key" forces are the internal forces of that loop of wire. The internal forces both keep the wire rigid and keep the electric charges that carry the current in the wire.
The magnetic field isn't directly causing the torque. The contact forces between the electric current and the rest of the wire is directly causing the torque.
The wire of the loop has two components. One is the free electrons in the wire. The other is atoms of the wire, including both bound electrons and nuclei.
Think of a single conduction electron in the copper wire. The copper wire is initially still in the laboratory frame. The electron initially moves perpendicular to the magnetic field of the bar magnet. The magnetic field causes a force that is perpendicular to the electrons motion. No work is done by the magnetic field, as you said.
The electron can't leave the copper wire. When the wire gets to the edge of the copper wire, it has to slow down. The edge of the copper wire applies a force to the electron which stops it from jumping into the air. One could describe this as a contact force (i.e., a sharp wall). Or maybe one would prefer to think of it as electrostatic attraction of the electron and the positive ions in the copper wire. In any case, a force is applied to the electron by the edge of the wire that slows the electron down.
For every action, there is a reaction (Newton's third law). When the electron nears the edge of the copper wire, it applies a force on the edge that is equal and opposite the force that the edge applies on the electron. Hence the electron is applying a force to the wire.
The force of the electrons on the wire is what causes the torque. The force is not directly caused by the bar magnet. If the electrons were not bound by the wire, then there would be no work done. However, the wire keeps the electrons in place. The forces that keep the electrons in place are not from the bar magnet. The forces that keep the electrons in place have to be accounted for in some way.
You made an identification between the electric charges, the electric current and the wire. The electric charges carry the current. The electric charges that carry the current are only part of the wire. The rest of the wire is necessary to keep the electrons flowing on the path of the wire. The magnetic field of the bar magnet does no work on the electric charges that make up the current.
When your instructor said that magnetic fields can't do work on the current, he was literally correct. However, he did you a bit of a disservice. This type of rule has to be used with caution. The path of the electric current in a wire is constrained by the shape of the wire. Therefore, the forces that keep the electric current in the wire can't be ignored. Constraints imply forces that aren't always explicit in the wording of the problem.

Lesson for engineers: Always take into account the constraints, because the constraints imply internal forces.
Lesson for physicists: Boundary conditions are always important, especially those caused by constraints.

Ref bold quote - this is OOTA science (out of thin air). Where did you get this? Source/reference please. "The edge applies a force" to the e-" Indeed? The edge, just what is "the edge"? Atomic nuclei at the outer layer, free electrons at outer layer, just what, may I ask, is this "edge" which applies a force?

Although there are inner forces in the wire which "hold" the electron preventing it from jumping away, these forces do not impart motion to the wire. I explained the motion, how it is derived, along with others, in my link found in my previous post. If you wish to discuss how the force on the wire is generated, please review the thread I linked to, then feel free to raise questions, or challenge my position, or that of others.

Also, not to be personal, but what is the extent of your background regarding e/m fields, energy conversion (transformers, motors, generators, relays, etc.), relativity, quantum mechanics, etc.? This forum is a good one, expecting posters to provide proof, theory, empirical measurement, etc. as support for what they state. To simply state "this is how it really works" without anything to back it up, is nothing but dust in the wind. Again, I do not question your intelligence, but I ask just how you know that what you claim is true, when it runs counter to established motor/generator/e/m fields theory, practice, & observation? Best regards.

Claude

 

[Darwin123]

Ref bold quote - this is OOTA science (out of thin air). Where did you get this? Source/reference please. "The edge applies a force" to the e-" Indeed? The edge, just what is "the edge"? Atomic nuclei at the outer layer, free electrons at outer layer, just what, may I ask, is this "edge" which applies a force?

Although there are inner forces in the wire which "hold" the electron preventing it from jumping away, these forces do not impart motion to the wire. I explained the motion, how it is derived, along with others, in my link found in my previous post. If you wish to discuss how the force on the wire is generated, please review the thread I linked to, then feel free to raise questions, or challenge my position, or that of others.

Also, not to be personal, but what is the extent of your background regarding e/m fields, energy conversion (transformers, motors, generators, relays, etc.), relativity, quantum mechanics, etc.? This forum is a good one, expecting posters to provide proof, theory, empirical measurement, etc. as support for what they state. To simply state "this is how it really works" without anything to back it up, is nothing but dust in the wind. Again, I do not question your intelligence, but I ask just how you know that what you claim is true, when it runs counter to established motor/generator/e/m fields theory, practice, & observation? Best regards.

Claude

My background in e/m fields, electronics, relativity and quantum mechanics is pretty strong. I have added some information on my personal profile, open to registered users of this forum. I have not included any information specific enough to track me. You can believe what you want about me. Whatever you think, I have heard worse.
What I wrote is somewhat straightforward for physicists and engineers. I don't think that I have to provide empirical evidence for a simple idea. I was referring to your own diagram and your own words. I think that your diagram is not completely labeled. You did not label the relevant forces, their direction or the point they are acting on. You also did not mention the relevant physical constraints, such as the current having to follow the rigid wire. You also didn't what object the work is being done on.
In my coursework and experience, one can't have a physical constraint without a corresponding force or a force equivalent. One can "eliminate" the force using a change of variable. This leads to the concept of generalized forces. However, you one can't eliminate a physical constraint by ignoring it.
The charge carrier in the circuit are physically constrained to the wire by some type of force, the details of which are unimportant in your problem. The important point here is that the charge carriers are not the entire wire. The wire also contains a medium that maintains the circuit. The wire, carrier and medium, constitutes a rigid body.The wire itself is physically constrained to keep its shape by rigid body forces. Unless there was some type of force on the charge carrier, other than the magnetic field, the charge carrier would leap from the wire. Thus, the path of the carrier is constrained by internal forces.
I am using the phrase "charge carrier" to distinguish it from free electrons. According to solid state physics, there are all sorts of carriers that may be carrying the charge. Fortunately, it doesn't matter precisely what the charge carrier is. The charge carrier is traveling in a metallic medium that may be crystalline. Fortunately, I doesn't matter precisely what this medium is. It can be amorphous, or a polymer. All that matters is that there is a force between the medium and the carrier such that the carrier can't leave the wire.
The magnetic field can create a force on the medium, merely by applying a force to the carrier. The magnetic field pushes the carrier, which pushes the medium. However, the direction of the force exerted by the medium on the carrier is in the opposite direction of the direction of motion of that carrier. Therefore, the force keeping that carrier in the medium is doing work on the carrier.
Repeat: The direction of the force of the medium on the carrier is not the same as the direction of the magnetic force on the carrier. The medium can do work on the carrier. Therefore, the carrier can do work on the medium.
Your diagram shows a rigid loop of wire on an axle rotating in a magnetic field. The work is being done by the rigid loop of wire on a wheel that you labelled the commutator.
The internal forces of a rigid body cancel out. The wire, carriers and medium, is rigid. Therefore, you can ignore the internal forces only if you treat the wire as one rigid body. A free carrier in the wire actually has two forces on it: the force of the magnetic field and the force of the medium. So unless you want to analyze the details of the medium, you have to treat the entire wire as a single object. You can't look at the carrier as somehow being isolated from the medium.
If you are asking about the work being done on the commutator, then you should draw the commutator by itself as well as the force vectors that are working on it. If you do so, then you will notice that the magnetic field isn't even touching the commutator. Therefore, the magnetic field can't be doing work on the commutator.
The only force on the commutator is a contact force coming from the rigid loop of wire. The rigid wire contains a substrate and the charge carrier, whatever it is.
If you want to know about the work done on the loop of wire, draw the force diagram of the loop of wire by itself without the magnet and without the commutator. Then draw the forces. There is the force of the magnet on the left side of the wire, the force of the magnet on the right side of the wire, the force of the commutator on the right side of the wire, and the force of the commutator on the left side of the wire.
The rigid loop of wire is at equilibrium. Please note that at equilibrium, the total force on the rigid loop has to be zero and the total torque on the rigid loop has to be zero.
The external forces are the contact forces on the commutator and the force of the magnetic field on the free carrier. As I mentioned, the force of the free carrier on the medium is an internal force. It cancels out the force of the medium on the free carrier. and so can be ignored. Therefore, the strength of the torque (and force) of the commutator has to be equal and opposite in sign to the torque (and force) of the magnetic field.
Your teacher told you that a static magnetic field can't do work on a current. He should have said that the static magnetic field can't do work on a electric charge. However, that doesn't mean that the electric charge can't do work on another electric charge in its vicinity.
What you asked about is the work done on macroscopic systems. Like the wire. Like the commutator. You did not ask what work was done on the charge carrier. However, here is the answer. Work is being done on the charge carrier by the medium that it is embedded in. The charge carrier is being forced by the medium to move in a different direction than it would if only the magnetic field was acting on it. Therefore, the magnetic field is indirectly doing work on the medium.

 

[cabraham]

My background in e/m fields, electronics, relativity and quantum mechanics is pretty strong. I have added some information on my personal profile, open to registered users of this forum. I have not included any information specific enough to track me. You can believe what you want about me. Whatever you think, I have heard worse. --- --- --- --- --- Therefore, the magnetic field is indirectly doing work on the medium.

Darwin you quoted me, then obviously replied to someone else. I asked you to review my link from a previous thread, which I gave and here it is again:

https://www.physicsforums.com/showthr...=347539&page=4

I just want to know what you have to say about the linked comments. I believe we examined this issue quite thoroughly.

Claude

 

[Darwin123]

I'm just confused...

I know that magnetic fields can do work only on pure magnetic dipoles like a bar magnet. Based on the formula, the magnetic force on a charge is qv⃗ ×B⃗ which is identically perpendicular to v⃗ and that's why it does no work. However, forces on magnetic dipoles and more general objects don't have the form v⃗ × - they're not perpendicular to v⃗ , so they do work in general.

But still when I look at this picture I get confused:

http://ecommunity.pwsd76.ab.ca/file.php/1030/moddata/resource/23766/physics_30/images/m4/103_dc_motor.jpg

In this picture aren't magnetic force causing the rotation of the loop! Aren't the magnetic forces in a motor on of the key! Factors of motion within it? I mean it makes no sense to me why in this cause magnetic force can't do work on an electric charge... Could someone pelase help me out with this!

Here is a real simple explanation.
The way you drew it, the charge carriers are moving on a path that is perpendicular to the force of the magnet. This is true only when the loop of wire is standing still. When the loop of wire is standing still, the magnet is not doing work on the loop of wire.
When the wire is turning, the charge carrier is forced by the wire to move such that its velocity has a small component parallel to the force of the magnet. Therefore, the magnet is doing force on the charge carrier.
The charge carrier would have no component of velocity parallel to the magnetic force if there were no internal forces making the loop of wire rigid. The forces that keep the wire rigid are responsible for making the loop of wire move in circles. Thus, the medium of the wire is providing the centripetal force necessary to prevent the loop of wire from flying to pieces. It is the centripetal force on the charge carrier that causes the magnet to do work.
So basically, you should add a component of electric current that is tangential to the motion of the wire. The tangential component of velocity will be proportional to the tangential velocity of the the wire, and to the charge on the charge carrier.
The hypothesis that the velocity of the wire adds to the velocity of the charge carrier takes into account the internal forces that hold the wire rigid. As long as you calculate that velocity of the wire correctly, you don't need to draw the internal force on the charge carrier.
Of course, it works out in units. The contribution of force from the current is in units of current times length times magnetic field strength. The contribution of force from the tangential velocity of the wire is in units of charge times speed times magnetic field strength. They are the same units.
A real electric motor will take time to start. Until it starts spinning rapidly, it won't draw power effectively from the commutator. Until the loop starts moving, most of the energy is wasted as resistive heat energy.
The way that I just described it is physically equivalent to the description in the other post. In both posts, the thing that makes the magnet do work is the internal force that keeps the charge carrier moving in the wire.
What I forgot in the other rambling post is that the work formula uses the total velocity of the charge carrier. The velocity of the charge carrier in a wire is different from the velocity of a free electron. The motion of the wire adds to the motion of the charge carrier. Hence, you don't have to know the precise functional expression for the internal forces.

 

[Philip Wood]

Take the simple case of two parallel wires carrying currents in the same direction. They attract each other. If we allow them to move together, work is done on them (by definition of work). They will acquire KE. This energy will have come from the batteries urging the currents. This is because there is a back-emf due to the wires moving and cutting each others' flux lines.

As the wires move together their charge carriers are experiencing motor effect forces opposing their motion forward through the wire. Extra work has to be supplied by the batteries to maintain the current. This work is 'passed on' as the work done on the wires as they are made to accelerate towards each other.

The force (acting when the wires move towards each other) on the charge carriers in a direction parallel to the wire is made, by the wonders of the Motor Effect (Magnetic Lorentz force) to produce a force at right angles to the wire. It's not really the magnetic field which is doing work. It's a bit like a piece of string going over a quarter of the circumference of a pulley, and so bending through an angle of 90°. If we pull one end of the string, the other end can do work, but it's the puller, not the pulley, that supplies the work.

 

[Philip Wood]

Here is a simple mathematical treatment of what I was trying to say in my last post.

 

[Darwin123]

Take the simple case of two parallel wires carrying currents in the same direction. They attract each other. If we allow them to move together, work is done on them (by definition of work). They will acquire KE. This energy will have come from the batteries urging the currents. This is because there is a back-emf due to the wires moving and cutting each others' flux lines.

As the wires move together their charge carriers are experiencing motor effect forces opposing their motion forward through the wire. Extra work has to be supplied by the batteries to maintain the current. This work is 'passed on' as the work done on the wires as they are made to accelerate towards each other.

The force (acting when the wires move towards each other) on the charge carriers in a direction parallel to the wire is made, by the wonders of the Motor Effect (Magnetic Lorentz force) to produce a force at right angles to the wire. It's not really the magnetic field which is doing work. It's a bit like a piece of string going over a quarter of the circumference of a pulley, and so bending through an angle of 90°. If we pull one end of the string, the other end can do work, but it's the puller, not the pulley, that supplies the work.

Good. Consider two wires in parallel with parallel electric currents. Both currents are perpendicular to a static magnetic field.
You are suggesting a calculation of work using the KE and the EMF as intermediate quantities in the calculation. This is an entirely good way to solve the problem. However, the work can be calculated without doing an intermediate calculation of either KE or EMF. The work can be calculated using only the definition of work, the Lorentz force law, and the law of Biot and Savart.
This is more consistent with what the OP is asking. The OP seems to be questioning the consistency between the Lorentz force law and the conservation of energy. Students often learn about the Lorentz force law before they learn about EMF. The calculation of EMF requires one to know about time varying magnetic fields and inertial frames. This should not be absolutely necessary if there is an inertial frame where the magnetic field is static.
Consider the case of two parallel wires with parallel electric currents. The first wire, #1, exerts an attractive force on the second wire, #2, because of the magnetic field the current of #1 generates. The work on wire #2 can be calculated in the inertial frame where the magnetic field is static and homogeneous.
If the force is stationary and homogeneous, then the force time distance where the distance is measured in the direction of motion. If the force is inhomogeneous, an integral is needed. However, for small distances, one can consider the magnetic field effectively homogeneous and stationary.
If there is no motion, then there is no work. This is true regardless of how strong the force of attraction is. I will be more specific. If wire #2 is stationary, the wire #1 can not do any work on wire #2. Zero distance means zero work.
If wire #2 is not moving, then the electric charge carrier is moving in a direction perpendicular to the force created by the magnetic field of wire #1. If wire #2 is not moving, the force exerted by wire #1 can not do work on the charge carrier of wire #2.
You may say that wire #2 must move if wire #1 is acting on it. However, wire #2 can remain stationary if some force other than the magnet is holding it in place. For instance, the wire may be fastened to a wall. The contact force of the wall holds the wire still. Therefore, it is quite possible for wire #1 to do no work on wire #2 even though it exerts a force.
Now, unfasten wire #2 from the wall. Let wire #2 move toward wire #1. Look at the electric charge carrier in wire #2.
The electric charge carrier now has two components of motion instead of one. The electric charge carrier still is moving due to the electric current. However, the electric charge carrier is now being dragged by the rest of the wire #2 toward wire #1. Therefore, the velocity is no longer perpendicular to the force exerted by wire #1.
The is a component of velocity of the charge carrier in the direction of the motion. The force times the distance in the direction of motion is the work exerted on the charge carrier by wire #1.
So the body giving off the magnetic field, wire #1, does work on the charge carrier of wire #2. The magnetic field is doing work, but only if wire #2 is allowed to move.
The analog to electric motors should be obvious. Obviously, an electric motor can only do work on something if it is moving. As a consequence, an electric motor draws more power when it is turned on than when it is off. If you stop an electric motor from moving, then it will draw less power.
The Lorentz force law is consistent with the conservation of energy. As in most problems, one has a choice as to whether one solves the problem using dynamic variables (like force) or conserved quantities (like energy). The two approaches should be and are self consistent.
The question concerned the work done by an electric motor. I think the important point here is that the motion of the electric motor changes the motion of the charge carrier in the circuit. Therefore, the motion of the wire has to be taken into account. There is more than one way to take the motion of the wire into account. However, the motion of the circuit components can not be ignored.
One more thing. Someone here claimed that there is no internal force involved in the Hall effect. There are forces involved in the Hall effect that usually aren't discussed. When a voltage is developed via the Hall effect, there is a stress on the conductor caused by the magnetic field. If an aqueous solution of salt were used instead of a conductor, there would be stretching of the fluid caused by the magnetic field. However, the Hall effect is usually demonstrated with a solid metal. So the internal forces prevent the metal from stretching.

 

[Philip Wood]

Darwin123: I'm sorry that I didn't provide my thumbnail (post 13) at the same time as my qualitative (hand-waving) explanation (post 12). I think you'll find that post 13 does pretty much what's needed using just the Lorentz force (magnetic component).

 

[Darwin123]

Darwin123: I'm sorry that I didn't provide my thumbnail (post 13) at the same time as my qualitative (hand-waving) explanation (post 12). I think you'll find that post 13 does pretty much what's needed using just the Lorentz force (magnetic component).

Yes, it does. Your handwritten equations in post 12 are precisely what I meant. I recommend that read that post to anyone who still has a question.
I don't yet know how to get equations and graphics onto my posts. I try to paint a picture with words.
Better yet, I would like to be able to modify the pictures and equations that people send. If all the velocity components on the charge carrier could be drawn into the illustration of the OP, it would be a lot clearer. One extra arrow on the current. showing the extra velocity component, would make the point a lot clearer.

 

[truesearch]

'The way you drew it, the charge carriers are moving on a path that is perpendicular to the force of the magnet. This is true only when the loop of wire is standing still. When the loop of wire is standing still, the magnet is not doing work on the loop of wire.
When the wire is turning, the charge carrier is forced by the wire to move such that its velocity has a small component parallel to the force of the magnet. Therefore, the magnet is doing force on the charge carrier.'
In practice an electric motor has a (uniform!) radial field, how does this influence this part of the explanation?

 

[truesearch]

Not the original question but... what would happen if the wire had no edges to keep the 'charge carriers' in.
If the wire loop became a cylinder, as per diagram. Is this an electric motor?
Is work being done?

 

[Philip Wood]

Darwin123

Thank you.

Equations can be done in PF using Latex. There's a compact summary under the Sigma at the right of the ribbon of icons when you choose 'go advanced' for your post. There are fuller guides on the internet.

The advanced option also allows you to import things as attachments. If I want to put in diagrams, or a mixture of diagrams and equations, I hand-write, scan and import. Quick but not very elegant!

 

[Miyz]

Here is a real simple explanation.
When the wire is turning, the charge carrier is forced by the wire to move such that its velocity has a small component parallel to the force of the magnet. Therefore, the magnet is doing force on the charge carrier.
The charge carrier would have no component of velocity parallel to the magnetic force if there were no internal forces making the loop of wire rigid. The forces that keep the wire rigid are responsible for making the loop of wire move in circles. Thus, the medium of the wire is providing the centripetal force necessary to prevent the loop of wire from flying to pieces. It is the centripetal force on the charge carrier that causes the magnet to do work.

I'd like to add... A conclusion.

The magnetic fields created by the permanent magnets are doing work BASED on the forces within the wire(They need each other to process this work most complicated system do this process).

Darwin123, based on what you said. I believe there are multiple forces in the "motor effect" that do a "net work".

Each force is acted on another and eventually work would be done and energy will be transfered.

Hence again my reference to this law F = IL x B
The greater the force the more work is being done on that "loop" of wire and more energy would be transfered.


(This is my conclusion based on all of you're posts + the basic laws on this matter + math. Please correct me if I'm wrong.)

Do you all agree with this conclusion?

 

[Philip Wood]

Miyz
(1) ILxB is the sum of the qvxB magnetic Lorentz forces on the charge carriers in the wire, and since this force is at right angles to v, it can never do any work on a charge carrier. In a nutshell, vdt.q(vxB) = qdtB.(vxv) =0.

(2) However, as I tried to explain in posts 12 and 13, zero work being done by B on q is consistent with equal quantities of work being done on q and by q. What makes this non-trivial for the current-carrying wire moving at right angles to itself in a magnetic field is that the forces associated with the input work and the output work are at right angles to each other.

In the case of the loop of current-carrying wire turning in the magnetic field, work is done by the carriers on the wire (via essentially electric field forces) enabling the loop to do work via the motor spindle on some external load. Work is done on the carriers by the battery driving the carriers through the coil. [This work is additional to the work done against electrical resistance.] It shows up as the back emf in a motor when running.
Post 13 shows how this comes about, in terms of forces and velocities. The argument applies to any wire in a magnetic field.

 

[cabraham]

Miyz
(1) ILxB is the sum of the qvxB magnetic Lorentz forces on the charge carriers in the wire, and since this force is at right angles to v, it can never do any work on a charge carrier. In a nutshell, vdt.q(vxB) = qdtB.(vxv) =0.

(2) However, as I tried to explain in posts 12 and 13, zero work being done by B on q is consistent with equal quantities of work being done on q and by q. What makes this non-trivial for the current-carrying wire moving at right angles to itself in a magnetic field is that the forces associated with the input work and the output work are at right angles to each other.

In the case of the loop of current-carrying wire turning in the magnetic field, work is done by the carriers on the wire (via essentially electric field forces) enabling the loop to do work via the motor spindle on some external load. Work is done on the carriers by the battery driving the carriers through the coil. [This work is additional to the work done against electrical resistance.] It shows up as the back emf in a motor when running.
Post 13 shows how this comes about, in terms of forces and velocities. The argument applies to any wire in a magnetic field.

https://www.physicsforums.com/showthr...=347539&page=4

Please review the above link & comment. I believe we've already examined these issues & came up with a conclusion many were pleased with. It involves internal electric forces.

Claude

 

[Philip Wood]

Claude: Link doesn't work (for me). Can you remember the name of the thread or (roughly) when it was active?

 

[cabraham]

Claude: Link doesn't work (for me). Can you remember the name of the thread or (roughly) when it was active?

https://www.physicsforums.com/showthread.php?p=2413237#post2413237

I tried it & it worked. Let me know what you think. We concluded that magnetic, electric, & strong nuclear forces all participate.

Claude

 

[Miyz]

https://www.physicsforums.com/showthread.php?p=2413237#post2413237

I tried it & it worked. Let me know what you think. We concluded that magnetic, electric, & strong nuclear forces all participate.

Claude

I find that you're conclusion is very very well put. And I totally agree!

I feel this topic is not popular and the understanding of magnets,magnetic force/fields is not fully understood. In a motor for example some would say that its the magnets doing work... They appear to.However, they act as a fundamental key part for this whole "chain reaction" to accrue. Could possibly say like a key for a door. Without it, the door won't be opened, and NO WORK. is done.

Maybe an analogy would help. A steel ball is tethered to a rubber ball via a short cord, or even glued together. A powerful electromagnet is held above the tethered ball pair. The em is turned on and the steel/rubber ball pair is lifted into the magnet.

I certainly do not believe that a magnet is doing work on the rubber ball. But the rubber ball does not ascend if not for the mag force. So it is really splitting hairs to argue which force is responsible for the rubber ball ascending.

The mag force acting on the steel ball is what ultimately lifted both balls. The steel ball was lifted by the magnet directly. The rubber ball was lifted indirectly. The tether provided the means for the rubber ball to tag along with the steel ball.

With 2 parallel wires, the E force between the lattice and free electrons is the tether. The H force dictates where the electrons go, then the E force tethers the lattice yanking it in the direction of the electrons. To say that H is NOT responsible for the lattice moving is like saying that the magnet is NOT responsible for the rubber ball ascending. The electrons and the lattice are tethered via E force. But the H force is what moves the electrons, and is ultimately responsible for moving the lattice. The E force does indeed move the lattice, but the E force magnitude and direction is dictated by the location of the electrons which is dictated by the magnitude and direction of H.

It's difficult to separate the 2 forces. But it is clear as day that H is what dictates the magnitude and direction of the displacement of the wires. E follows H. I know that E & H are inclusive, and neither is the cause of the other. But under these narrow conditions, H is ultimately in control, with E tagging along.

H, however, is not more fundamental than E, nor less. They are inclusive.

I applaud you for that conclusion!

 

[Philip Wood]

The second link you provided worked fine. We seem to be in agreement that it's essentially the magnetic forces on the charge carriers that are of interest here, and that, in your words, "With 2 parallel wires, the E force between the lattice and free electrons is the tether. The H force dictates where the electrons go, then the E force tethers the lattice yanking it in the direction of the electrons." We lose very little understanding, in my opinion, if we think of the charge carriers as beads constrained to move along a rail.

 

[Miyz]

Many objects that do work, Can relie on one force. While others require multiple forces to do work.

In a sense a net.Force has to be calculated and then the net.Work would be found.
We've discovered so much things in our time! Now, were only getting to the even harders questions!

 

[cabraham]

Thanks for the feedback. Also worth pondering is that the lattice neutrons cannot be moved by an E field. The nuclear strong force, SF, is what yanks the neutrons along the same direction as the protons which are yanked towards the electrons. So H/B yanks on the elctrons, the E/D force yanks on the protons, & the SF yanks on the neutrons. But the magnetic force must be strong enough to move the whole package, electrons/protons/neutrons.

Using the electromagnet/balls analogy, if we have 3 balls, steel, rubber, & wood, then the em lifts all 3 if they are tethered. Using mass proportional to electron/proton/neutron, if the steel ball is very small, say 1 gram mass, & the rubber ball is 1,836 gram mass, & the wood ball is 1,837 gram mass, then the electromagnet must exert enough force on the steel ball to lift all 3 balls. Hence the em exerts a force on the tethered trio of 3,674 gram force.

No other explanation makes any sense. The magnetic force can only move a charge that is in motion, i.e. the electron. The lattice protons are stationary & cannot be moved by magnetic force. Obviously an electric force is needed to move these protons. But it doesn't end there because an electric field exerts no force upon a neutron. At least half of the total mass of the wire is in the form of neutrons. Only strong force can account for neutron motion. The magnetic field varies with the current, and as it varies, the E force & strong force vary in accordance. The magnetic force is in control, SF & E force tag along like an obedient shadow. Amazing!

Anyway, these thought problems are really fun to ponder. They make us think. I believe we all have a better understanding of this issue now. Cheers.

Claude

 

[Darwin123]

'The way you drew it, the charge carriers are moving on a path that is perpendicular to the force of the magnet. This is true only when the loop of wire is standing still. When the loop of wire is standing still, the magnet is not doing work on the loop of wire.
When the wire is turning, the charge carrier is forced by the wire to move such that its velocity has a small component parallel to the force of the magnet. Therefore, the magnet is doing force on the charge carrier.'
In practice an electric motor has a (uniform!) radial field, how does this influence this part of the explanation?

You would have to rely on integrals rather simple products. Work would be an integral of the force with respect to the distance along the path. This would be the same as summing the different contributions of work from infinitesimal segments of the path, where the force is effectively constant over each infinitesimal segment.
This is a mathematical issue. I don't think it relates to the physical conundrum brought up by the OP.

 

[Darwin123]

I'd like to add... A conclusion.

The magnetic fields created by the permanent magnets are doing work BASED on the forces within the wire(They need each other to process this work most complicated system do this process).

Darwin123, based on what you said. I believe there are multiple forces in the "motor effect" that do a "net work".

Each force is acted on another and eventually work would be done and energy will be transfered.

Hence again my reference to this law F = IL x B
The greater the force the more work is being done on that "loop" of wire and more energy would be transfered.(This is my conclusion based on all of you're posts + the basic laws on this matter + math. Please correct me if I'm wrong.)

Do you all agree with this conclusion?

I agree that the work is done be several forces. However, that requires a bit of semantics.
In common usage, work is done by the system providing the energy. If a person used a bicycling generator to provide the current, then he would have to work harder to keep the current going. However, he is not applying force directly to the motor.
I would say that the magnetic isn't really doing work at all. The energy isn't providing the energy. It is only supplying the force.
In a lever problem, we seldom say that the lever is doing work. The person pushing down on the lever is doing work. The internal forces of the lever are the ones that end up pushing the object that is being lifted. However, the work is done only by the system that provides the energy.
Therefore, I would turn your idea around a bit. Instead of saying,
I believe there are multiple forces in the "motor effect" that do a "net work".
I would say,
I believe the electric current in the wire does the "net work". Multiple forces cause the motor effect.
The forces exerted by the magnet and wire on the carriers cause the "motor effect." Since the work of internal forces cancel out, I can't see how the internal forces can be said to do work.
I world restrict the phrase "doing work" to the system that provides the energy and not the forces that change direction.
This idea may also be useful in thermodynamics. In the case of the Carnot cycle, the cylinder with the gas is filled with gas molecules. Each gas molecule hitting the piston does work on the piston. The force of each gas molecule on the piston is different. However, these are internal forces. In the end, the contribution of the gas molecules averages out to one parameter which is the pressure. It is the gas in the cylinder that does the work, not the forces of the individual molecules.

 

[Miyz]

I agree that the work is done be several forces. However, that requires a bit of semantics.
In common usage, work is done by the system providing the energy. If a person used a bicycling generator to provide the current, then he would have to work harder to keep the current going. However, he is not applying force directly to the motor.
I would say that the magnetic isn't really doing work at all. The energy isn't providing the energy. It is only supplying the force.
In a lever problem, we seldom say that the lever is doing work. The person pushing down on the lever is doing work. The internal forces of the lever are the ones that end up pushing the object that is being lifted. However, the work is done only by the system that provides the energy.
Therefore, I would turn your idea around a bit. Instead of saying,
I believe there are multiple forces in the "motor effect" that do a "net work".
I would say,
I believe the electric current in the wire does the "net work". Multiple forces cause the motor effect.
The forces exerted by the magnet and wire on the carriers cause the "motor effect." Since the work of internal forces cancel out, I can't see how the internal forces can be said to do work.
I world restrict the phrase "doing work" to the system that provides the energy and not the forces that change direction.
This idea may also be useful in thermodynamics. In the case of the Carnot cycle, the cylinder with the gas is filled with gas molecules. Each gas molecule hitting the piston does work on the piston. The force of each gas molecule on the piston is different. However, these are internal forces. In the end, the contribution of the gas molecules averages out to one parameter which is the pressure. It is the gas in the cylinder that does the work, not the forces of the individual molecules.

I would agree with you if you'd say magnets do a "part" of the total work. As you said its all about the force supplied by the battery. Which then creates multiple forces within the wire.
As I said before, without the presence of a B field, no work would be done. Indeed the electrical forces are the main reason why this whole process would occur.However, without the existence of a magnet/electromagnet etc... No work will be done and the motor effect wouldn't be created.

Here's an example of what I mean:

Take a computer... You'd agree that a processor is a key element of the system like a permanent magnet in a motor. Now a processor is pointless without what? A motherboard! To link it with the other parts of the system. Hence in a way the motherboard acts like the electrical forces or viceversa. Without one element the other can't do anything. When both are present something can occur.

If you'd say magnets alone do the work, I would not agree. If you'd say the electrical force alone are doing work, hmm... I'd still not agree. If you'd say BOTH forces do the work. I would clap and agree .

You know Darwin123, its all linked to one another. We can't point out one culprit and say it did all the work now can we? We would assume that there was an associate in this whole business lol,

Again I would reifer to this law: F = IL x B, The magnetic force applied on the wire is created from both I & B, Without them both nothing would happen, A force would be present but no work would be done. I do acknowledge all the inner force generated by the electrical force, all the small part that make up the whole force and I do agree that "force" is supplied by the battery in a distance. When we break done energy you'd find its all about the forces

 

[Miyz]

What an interesting discussion this turned out to be. I found that I understood more and more of this effect. Wonderful!

I appreciate all you're efforts everyone! Thank you all!

 

[cabraham]

I would agree with you if you'd say magnets do a "part" of the total work. As you said its all about the force supplied by the battery. Which then creates multiple forces within the wire.
As I said before, without the presence of a B field, no work would be done. Indeed the electrical forces are the main reason why this whole process would occur.However, without the existence of a magnet/electromagnet etc... No work will be done and the motor effect wouldn't be created.

Here's an example of what I mean:

Take a computer... You'd agree that a processor is a key element of the system like a permanent magnet in a motor. Now a processor is pointless without what? A motherboard! To link it with the other parts of the system. Hence in a way the motherboard acts like the electrical forces or viceversa. Without one element the other can't do anything. When both are present something can occur.

If you'd say magnets alone do the work, I would not agree. If you'd say the electrical force alone are doing work, hmm... I'd still not agree. If you'd say BOTH forces do the work. I would clap and agree .

You know Darwin123, its all linked to one another. We can't point out one culprit and say it did all the work now can we? We would assume that there was an associate in this whole business lol,

Again I would reifer to this law: F = IL x B, The magnetic force applied on the wire is created from both I & B, Without them both nothing would happen, A force would be present but no work would be done. I do acknowledge all the inner force generated by the electrical force, all the small part that make up the whole force and I do agree that "force" is supplied by the battery in a distance. When we break done energy you'd find its all about the forces

Actually there are 3 forces involved. Without strong nuclear force, SNF, the neutrons would not be moved. It takes all 3, magnetic, electric, & SNF. But it is important to emphasize that the currents in the field & armature windings (rotor & stator if you prefer), control the value of magnetic force, which results in electric & SNF matching the mag force.

Ultimately the value of interacting magnetic fields determine the torque. But this force acts only on electrons directly & relies on the E & SN forces to yank protons & neutrons along via tethering. This is why motor/generator theory places so much emphasis on magnetic forces & not the others. I believe that energy conversion is taught the right way at engineering colleges. Interesting discussion, thanks to all.

Claude

 

[Darwin123]

I would agree with you if you'd say magnets do a "part" of the total work. As you said its all about the force supplied by the battery. Which then creates multiple forces within the wire.
As I said before, without the presence of a B field, no work would be done. Indeed the electrical forces are the main reason why this whole process would occur.However, without the existence of a magnet/electromagnet etc... No work will be done and the motor effect wouldn't be created.

Here's an example of what I mean:

Take a computer... You'd agree that a processor is a key element of the system like a permanent magnet in a motor. Now a processor is pointless without what? A motherboard! To link it with the other parts of the system. Hence in a way the motherboard acts like the electrical forces or viceversa. Without one element the other can't do anything. When both are present something can occur.

If you'd say magnets alone do the work, I would not agree. If you'd say the electrical force alone are doing work, hmm... I'd still not agree. If you'd say BOTH forces do the work. I would clap and agree .

You know Darwin123, its all linked to one another. We can't point out one culprit and say it did all the work now can we? We would assume that there was an associate in this whole business lol,

Again I would reifer to this law: F = IL x B, The magnetic force applied on the wire is created from both I & B, Without them both nothing would happen, A force would be present but no work would be done. I do acknowledge all the inner force generated by the electrical force, all the small part that make up the whole force and I do agree that "force" is supplied by the battery in a distance. When we break done energy you'd find its all about the forces

I agree. The real issue here is how to draw the boundaries of our interacting systems. The boundary of an interacting system determines which are the internal forces and which are the external forces.
This is why I said that the issue was one of semantics. No boundary was drawn in the diagram. So different people here may be envisioning different subsystems. There are several composite bodies in the problem. What everyone says is correct, but they are talking about different composite bodies.

 

[Miyz]

Actually there are 3 forces involved. Without strong nuclear force, SNF, the neutrons would not be moved. It takes all 3, magnetic, electric, & SNF. But it is important to emphasize that the currents in the field & armature windings (rotor & stator if you prefer), control the value of magnetic force, which results in electric & SNF matching the mag force.

What do you mean by the SNF? &"important to emphasize that the currents in the field & armature windings (rotor & stator if you prefer), control the value of magnetic force, which results in electric & SNF matching the mag force."
Could you clarify this a bit more(Simpler way), I do understand the "tethered" part. But not sure what you're talking about hee...

Ultimately the value of interacting magnetic fields determine the torque. But this force acts only on electrons directly & relies on the E & SN forces to yank protons & neutrons along via tethering. This is why motor/generator theory places so much emphasis on magnetic forces & not the others.
Claude

Hence the idea of opposing and attracting magnetic fields.
E forces... Whats SN forces?

I thought by applying the magnetic force on the electron directly, an indirect force is applied on the proton and neutron?

 

[Miyz]

I agree. The real issue here is how to draw the boundaries of our interacting systems. The boundary of an interacting system determines which are the internal forces and which are the external forces.
This is why I said that the issue was one of semantics. No boundary was drawn in the diagram. So different people here may be envisioning different subsystems. There are several composite bodies in the problem. What everyone says is correct, but they are talking about different composite bodies.

I guess we truly need to breakdown things to the quantum level to understand how energy,force,work is all processed in this system. Interesting topic.

 

[cabraham]

What do you mean by the SNF? &"important to emphasize that the currents in the field & armature windings (rotor & stator if you prefer), control the value of magnetic force, which results in electric & SNF matching the mag force."
Could you clarify this a bit more(Simpler way), I do understand the "tethered" part. But not sure what you're talking about hee...



Hence the idea of opposing and attracting magnetic fields.
E forces... Whats SN forces?

I thought by applying the magnetic force on the electron directly, an indirect force is applied on the proton and neutron?

The tethering was explained in the link I referred to, from a thread in 2009. If you review the link then I will clarify if needed. SNF is the "strong nuclear force", which tethers the neutron & proton together. I brought it up simply because some suggest that the "E forces" are "really doing the work". I just wanted to remind all that an E field cannot move a neutron. The neutrons are roughly half the mass of any element/compound, except those with hydrogen. So neutron forces/motion cannot be explained with B or E forces, only SNF.

Have I helped? BR.

Claude

 

[Miyz]

The tethering was explained in the link I referred to, from a thread in 2009. If you review the link then I will clarify if needed. SNF is the "strong nuclear force", which tethers the neutron & proton together. I brought it up simply because some suggest that the "E forces" are "really doing the work". I just wanted to remind all that an E field cannot move a neutron. The neutrons are roughly half the mass of any element/compound, except those with hydrogen. So neutron forces/motion cannot be explained with B or E forces, only SNF.

Have I helped? BR.

Claude

Claude, Based on what you said and Darwin123. Is it safe to say: Magnetic field's can do work under certain circumstances? ONLY in the presence of both E forces + N forces can magnetic fields do work.

In a sense they are... So as E force, So as the N force.

They all were triggered in this even or "action" to do work. I would say this in a general simpler way:

Magnetic force can do work with the presence of E,force + N,force.
Electric force can do work with the presence of M,force + N,force.
N force can do work with the presence of M,force + E,force.

In a sense the motor effect... A simple effect CAN NEVER occur without the upper 3 rules.
They are all dependent on each other. without one of them. Nothing would happen.

Simple forces added up together to give the total work.

 

[cabraham]

Claude, Based on what you said and Darwin123. Is it safe to say: Magnetic field's can do work under certain circumstances? ONLY in the presence of both E forces + N forces can magnetic fields do work.

In a sense they are... So as E force, So as the N force.

They all were triggered in this even or "action" to do work. I would say this in a general simpler way:

Magnetic force can do work with the presence of E,force + N,force.
Electric force can do work with the presence of M,force + N,force.
N force can do work with the presence of M,force + E,force.

In a sense the motor effect... A simple effect CAN NEVER occur without the upper 3 rules.
They are all dependent on each other. without one of them. Nothing would happen.

Simple forces added up together to give the total work.

That sounds pretty reasonable to me. Several of us examined this exhaustively, & collectively we ascertained what you just said. Ultimately, though, I believe that the actual work is done by the power source driving the motor. Although energy can be stored in fields, then released to another entity, it is the power source, i.e. the wall outlet power mains, that is providing ALL the energy/power.

In a motor, of course all 3 forces work in unison, but it is safe to say that the magnetic forces, i.e. B/H, are the quantities that literally control the motor action. SNF & E tag along like an obedient shadow, but magnetic is in charge. Using my 3 ball analogy, a magnet lifts 3 tethered balls, steel, wood, & rubber. The magnet cannot lift wood and/or rubber, but it lifts them indirectly by lifting the steel ball directly, & relying on the E & SN tether forces to lift the rubber & wood balls.

But let us not forget, the magnet must provide a lifting force equal to the combined weight of all 3 balls. If each ball weighs a pound force, then the mag force must be 3 lbf. But the E & SN forces are only equal to the weight they carry. If the steel ball is on top, then E & SN provide 2 lbf, while the mag is 3 lbf. So the magnetic force is definitely the prime mover but it still relies on help from E & SN.

Interesting question. These puzzles get us thinking. I want to thank everybody here for being polite. These types of questions usually end up in a mud wrestling match. Everybody on this thread conducted themselves very well, & I take my hat off to all. I hope future discussions can be this civil. Best regards.

Claude

 

[Darwin123]

Claude, Based on what you said and Darwin123. Is it safe to say: Magnetic field's can do work under certain circumstances? ONLY in the presence of both E forces + N forces can magnetic fields do work.

In a sense they are... So as E force, So as the N force.

They all were triggered in this even or "action" to do work. I would say this in a general simpler way:

Magnetic force can do work with the presence of E,force + N,force.
Electric force can do work with the presence of M,force + N,force.
N force can do work with the presence of M,force + E,force.

In a sense the motor effect... A simple effect CAN NEVER occur without the upper 3 rules.
They are all dependent on each other. without one of them. Nothing would happen.

Simple forces added up together to give the total work.

And gravitational forces. Let us not forget those! Furthermore, you have to say what it does work on. I think that you are asking whether a magnetic field can do work on an electric charge or electric current.
I think the following is valid, but demonstrating it may sometimes be difficult.
ONLY in the presence of both E forces + N forces+gravitational forces can magnetic fields do work on an electric charge or electric current.

 

[cabraham]

And gravitational forces. Let us not forget those! Furthermore, you have to say what it does work on. I think that you are asking whether a magnetic field can do work on an electric charge or electric current.
I think the following is valid, but demonstrating it may sometimes be difficult.
ONLY in the presence of both E forces + N forces+gravitational forces can magnetic fields do work on an electric charge or electric current.

Other than gravity, we seem to have reached a unanimous agreement. But gravity is too weak to be concerned with as it is many orders of magnitude smaller than E, M, or N. Nonetheless, we cannot deny its presence, nor that of "W" (weak force", if such materials are present, but I don't think beta decay is present in motor materials).

Thanks again to all. BR.

Claude

 

[Miyz]

Ultimately, though, I believe that the actual work is done by the power source driving the motor. Although energy can be stored in fields, then released to another entity, it is the power source, i.e. the wall outlet power mains, that is providing ALL the energy/power.

When you break that down you'd realize that what the energy source is really just supplying the E forces within a distance. Already energy has been transferred on the wire, and work has been done.

I believe then the E force + SN force would interact with the M forces. We all should break down the concept of Work in, and Work out. Its more understanding when you would say the Forces in and the Netforce out. If you see where I'm going with this... It simply draws a better picture you can visualize it and understand everything more clearly then saying energy In and the energy converted(With respect to all laws, that's just my own way of understanding the relationship of energy,work,force all together).

Interesting question. These puzzles get us thinking. I want to thank everybody here for being polite. These types of questions usually end up in a mud wrestling match. Everybody on this thread conducted themselves very well, & I take my hat off to all. I hope future discussions can be this civil. Best regards.
Claude

Thanks! We should raise questions similar to this! To understand the truth about it more!

 

[Miyz]

Thank you all again for you're efforts!

 

[chingel]

It is important to note that magnetic fields apply forces only on moving charged particles, and for example in the the case of the electric motor, not on the wire itself but on the electrons.

I found this picture from google:

Consider a stationary particle that is on the path of the moving charged particle after it has moved through the magnetic field (for example where the arrow points that is with the text "Path of the particle"). The charged particle would collide with the stationary one after having gone through the magnetic field. Note that the magnetic field does no work on the charged particle, gives it no additional kinetic energy, only changes its direction. If there were no magnetic field, the particles wouldn't collide, but the magnetic field makes them collide and "makes" the second particle move. So it would seem that the magnetic field did work on the other particle, but it didn't, it simply redirected the first particle to hit something it otherwise wouldn't.

The energy to do the work came from the kinetic energy of the first particle, yet without the magnetic field the work couldn't not have been done on the other particle. Nevertheless, the magnetic field did no work, it simply redirected a particle's path.

In the case of the electric motor, the magnetic field would also simply change the paths of electrons, but would not give them any additional energy. The kinetic energy for the moving wire would come from the kinetic energy the electrons had before.

 

[Miyz]

It is important to note that magnetic fields apply forces only on moving charged particles, and for example in the the case of the electric motor, not on the wire itself but on the electrons.

I found this picture from google:

Consider a stationary particle that is on the path of the moving charged particle after it has moved through the magnetic field (for example where the arrow points that is with the text "Path of the particle"). The charged particle would collide with the stationary one after having gone through the magnetic field. Note that the magnetic field does no work on the charged particle, gives it no additional kinetic energy, only changes its direction. If there were no magnetic field, the particles wouldn't collide, but the magnetic field makes them collide and "makes" the second particle move. So it would seem that the magnetic field did work on the other particle, but it didn't, it simply redirected the first particle to hit something it otherwise wouldn't.

The energy to do the work came from the kinetic energy of the first particle, yet without the magnetic field the work couldn't not have been done on the other particle. Nevertheless, the magnetic field did no work, it simply redirected a particle's path.

In the case of the electric motor, the magnetic field would also simply change the paths of electrons, but would not give them any additional energy. The kinetic energy for the moving wire would come from the kinetic energy the electrons had before.

Um, if you say that magnets do no work... Check this out

1 - Yes they can,
2 - Why?
3 - Convinced?

If you still need some more "worded" detail check theses links out: 1, 2,

As I said before and I will say this again. Magnets/magnetic fields/etc... Are not understood fairly well... I mean so many attention went for complex idea how the most simplest products of nature and most important forces have been underrated...

 

[cabraham]

It is important to note that magnetic fields apply forces only on moving charged particles, and for example in the the case of the electric motor, not on the wire itself but on the electrons.

I found this picture from google:

Consider a stationary particle that is on the path of the moving charged particle after it has moved through the magnetic field (for example where the arrow points that is with the text "Path of the particle"). The charged particle would collide with the stationary one after having gone through the magnetic field. Note that the magnetic field does no work on the charged particle, gives it no additional kinetic energy, only changes its direction. If there were no magnetic field, the particles wouldn't collide, but the magnetic field makes them collide and "makes" the second particle move. So it would seem that the magnetic field did work on the other particle, but it didn't, it simply redirected the first particle to hit something it otherwise wouldn't.

The energy to do the work came from the kinetic energy of the first particle, yet without the magnetic field the work couldn't not have been done on the other particle. Nevertheless, the magnetic field did no work, it simply redirected a particle's path.

In the case of the electric motor, the magnetic field would also simply change the paths of electrons, but would not give them any additional energy. The kinetic energy for the moving wire would come from the kinetic energy the electrons had before.

But we're discussing forces between current carrying wires, akin to motor operation. We're not discussing collisions among particles. It has already been stated unanimously that a single charged particle, or several, moving through a magnetic field can only have its momentun changed, not its kinetic energy.

The rebuttal directly before this one by Miyz addresses what we've been talking about. When 2 current loops interact resulting in a net torque, we are examining the work done, forces involved, etc. Please review the link I gave earlier. Rather than repeat what has already been discussed, I will elaborate if you still have questions. Best regards.

Claude

 

[Miyz]

But we're discussing forces between current carrying wires, akin to motor operation. We're not discussing collisions among particles. It has already been stated unanimously that a single charged particle, or several, moving through a magnetic field can only have its momentun changed, not its kinetic energy.

The rebuttal directly before this one by Miyz addresses what we've been talking about. When 2 current loops interact resulting in a net torque, we are examining the work done, forces involved, etc. Please review the link I gave earlier. Rather than repeat what has already been discussed, I will elaborate if you still have questions. Best regards.

Claude

He should review you're thread and ours. Then he would understand our common conclusion about magnets doing work or not.(Again, THEY DO but UNDER CERTAIN circumstances)

 

[chingel]

But we're discussing forces between current carrying wires, akin to motor operation. We're not discussing collisions among particles. It has already been stated unanimously that a single charged particle, or several, moving through a magnetic field can only have its momentun changed, not its kinetic energy.

The rebuttal directly before this one by Miyz addresses what we've been talking about. When 2 current loops interact resulting in a net torque, we are examining the work done, forces involved, etc. Please review the link I gave earlier. Rather than repeat what has already been discussed, I will elaborate if you still have questions. Best regards.

Claude

A current through a wire is several charged particles moving. They feel the magnetic force, not the wire directly, and respond to the force by changing their direction and giving some of their momentum in the new direction to the wire, creating a force on the wire.

It should be similar to the collision. The direction of the electrons is changed and thus allowing them to do work on the wire by colliding with it. Otherwise the collisions would be chaotic, but the magnetic force changes the directions of the electrons in a consistent manner and allows the work to be done at the expense of the electrons kinetic energy, as in the case of a simple collision.

 

[Darwin123]

Other than gravity, we seem to have reached a unanimous agreement. But gravity is too weak to be concerned with as it is many orders of magnitude smaller than E, M, or N. Nonetheless, we cannot deny its presence, nor that of "W" (weak force", if such materials are present, but I don't think beta decay is present in motor materials).

Thanks again to all. BR.

Claude

Another assumption implicit in your diagram is that the permanent magnets don't move. This is one reason the magnetic field is static. If the magnets were allowed to move, then the problem would be more complicated.
The magnets keep their shape by rigid body forces. They may be held stationary on the horizontal plane also by rigid body forces. For instance, the mangets may be attached by glue to the horizontal surface. However, suppose the magnets are not attached directly to the plane.
If the magnets are not attached directly to the surface, then there has to be other forces involved. The magnets may have to be held still by a mixture of both gravity, contact force and static friction. The gravity prevents the magnet from moving up. The contact force (i.e., the normal force) prevents the magnet from sinking down. The static friction prevents it from moving in the horizontal plane.
Similarly, the wire loop has some weight. If the wire loop is not uniform in thickness, the unbalanced wire could be affected by gravity.
The weight of a single carrier may be negligible. However, the weight of other components in the system may not be negligible.
The discussion has turned to the contribution of nonmagnetic forces to the work done on the wire loop. The conjecture has been raised that maybe nonmagnetic forces "do work" in a motor. Gravity may well "do work" on a motor.
Fortunately, the problem can be solved without enumerating all the forces "that do work". The work done by most of those forces cancel out. By choosing the boundaries on the system properly, one can "hide" the forces that cancel out. In general, this is what has to be done.

 

[cabraham]

A current through a wire is several charged particles moving. They feel the magnetic force, not the wire directly, and respond to the force by changing their direction and giving some of their momentum in the new direction to the wire, creating a force on the wire.

It should be similar to the collision. The direction of the electrons is changed and thus allowing them to do work on the wire by colliding with it. Otherwise the collisions would be chaotic, but the magnetic force changes the directions of the electrons in a consistent manner and allows the work to be done at the expense of the electrons kinetic energy, as in the case of a simple collision.

An internal collision does not do work on the wire since conservation of momentum requires that the wire moves, i.e. undergo a momentum change, only when acted upon by an external force. This force is M. But, M exerts no force on stationary lattice protons & neutrons. Hence E & SN forces provide the tether force so that when M yanks on the electrons, the protons & neutrons are tethered along by E & SN forces.

Claude