# A light Interference doubt

sophiecentaur
Gold Member
I'm telling you again, change in field strength has no any direction and it can not produce any vectors or planes.
Get a grip. What's that supposed to mean?
Fields are in a particular direction - they are Vector quantities, for plane polarised waves, the fields lie in planes and change magnitude and sign. Nothing 'moves' anywhere. But what has any of this basic stuff about waves got to do with the nature of a photon? A photon has no 'size' and could be anywhere. Have you not read that?

Cthugha

No, I said electric current can be induced in a straight wire, meaning you don't need any loops. Read the links I posted there and learn about it if you don't know. It's only one guy in that thread that doesn't get it, and two other people confirmed what I said. You have no clue, but I like your attempts to discredit me, it's funny.
Two other people confirmed, that you can induce constant currents when having a loop. Without a loop, you induce a current for a short time, electrons pile up at one end of the wire and at some point the induced current and the current that is caused by the repulsion of the large number of electrons piled up cancel, so that there is no net current left. With a loop, there obviously is no pile up and you can induce constant current. But that has already been explained to you in that thread, but you preferred posting you strange view of things.

There are no any test charges in electromagnetic wave equation and they would surely not make E and B field oscillate perpendicularly to the direction of wave propagation and to each other.
The E field is defined via that force and now basically you want to tell us that the definition of some quantity does not matter?

You wish. This is what you said, and I quote: -"NO, the oscillations in an em wave do exactly not mean that. It is a change in the field strength along some direction. The change in field strength does not mean that something is literally moving up or down in this direction."

I'm telling you again, change in field strength has no any direction and it can not produce any vectors or planes.
So you are basically trying to tell me that the "change in the field strength along some direction" (what I have written) does not have any direction? The E-field is not a vector? This is pointless and you do not seem to be interested in physics, but just trolling. I think at this point, it is hopeless to try to get this topic carry some information along for others who might be interested in this topic, so the discussion with you ends here for me. I apologize to the one who opened the thread for being partially responsible that this thread which started out interesting has derailed.

Get a grip. What's that supposed to mean?
Get a clue. It means magnitude is a scalar number, thus has no any direction, so therefore change in field strength can not describe any plane and can not be perpendicular to anything.

Fields are in a particular direction - they are Vector quantities, for plane polarised waves, the fields lie in planes and change magnitude and sign.
No, fields can not be described by a single vector. They are not vector quantiites, they are three-dimensional 'vector fields'. A field can not be in a plane. Changing magnitude and sign of a field does not have any direction.

Nothing 'moves' anywhere. But what has any of this basic stuff about waves got to do with the nature of a photon? A photon has no 'size' and could be anywhere. Have you not read that?

- "The electric field is in a vertical plane and the magnetic field in a horizontal plane."

I ask you again, can you provide any reference that says those planes are not defined by spatial oscillation of E and B field, but some "force vectors" or whatever else?

sophiecentaur
Gold Member
You are hopelessly failing to support your mistaken opinion. I ask you again, can you provide any reference that says those planes are not defined by spatial oscillation of E and B field, but some "force vectors" or whatever else?
I shouldn't need to be doing that. To be honest, I can't find, anywhere, any statement that insists that a vector quantity has to involve movement or spatial displacement - can you? Searching for a statement that something 'not true' is, indeed 'not true' is a bit of a tall order. If you want to find what 'is true' then take your pic of any google link about what vectors are. You seem to have a problem with defining a Field in terms of its effect on a unit charge (or a unit mass, in the case of gravitational field). Again, that's how they're defined everywhere you care to look. One thing is certain - a Field is not a set of invisible arrows out there in space.
But I think you have got yourself in a hole and you're not actually sure what you are arguing about - and nor am I. Your basic idea is flawed and you haven't come up with any evidence that it isn't.
Why not try to learn something instead of arguing against nothing specific?

Two other people confirmed, that you can induce constant currents when having a loop. Without a loop, you induce a current for a short time, electrons pile up at one end of the wire and at some point the induced current and the current that is caused by the repulsion of the large number of electrons piled up cancel, so that there is no net current left. With a loop, there obviously is no pile up and you can induce constant current. But that has already been explained to you in that thread, but you preferred posting you strange view of things.
The argument has nothing to do with "constant" current. It's about whether you need a loop to induce current or can it be done with a straight wire.

The E field is defined via that force and now basically you want to tell us that the definition of some quantity does not matter?
No, I said change in magnitude is not what defines planes of E and B field oscillation.

So you are basically trying to tell me that the "change in the field strength along some direction" (what I have written) does not have any direction?

What direction? What defines that direction and the planes of oscillation? I'm telling you while magnitude does change that is not what defines those planes of oscillation, but it is change of position, i.e. lateral movement of those fields that defines those planes of oscillation. Can you provide any reference that says those planes are not defined by spatial oscillation of E and B field, but something else?

I shouldn't need to be doing that. To be honest, I can't find, anywhere, any statement that insists that a vector quantity has to involve movement or spatial displacement - can you? Searching for a statement that something 'not true' is, indeed 'not true' is a bit of a tall order. If you want to find what 'is true' then take your pic of any google link about what vectors are. You seem to have a problem with defining a Field in terms of its effect on a unit charge (or a unit mass, in the case of gravitational field). Again, that's how they're defined everywhere you care to look. One thing is certain - a Field is not a set of invisible arrows out there in space.
But I think you have got yourself in a hole and you're not actually sure what you are arguing about - and nor am I. Your basic idea is flawed and you haven't come up with any evidence that it isn't.

- "From the viewpoint of an electromagnetic wave traveling forward, the electric field might be oscillating up and down, while the magnetic field oscillates right and left..."

What part of oscillating "up and down" or "left and right" is not clear to you? What else could be oscillating but their lateral position? And if it is something else why was it not mentioned?

You don't need to find a statement that is not true, you only need to find a statement that says what is true, and if that is not spatial oscillation then that statement would say what actually is, like "force vectors" as you said, or whatever else. Can you?

Why not try to learn something instead of arguing against nothing specific?
It is very specific, you just refuse to accept it, because you have fallen in love with complications and mysteries of Quantum Mechanics.

sophiecentaur
Gold Member
Until you realise that Vectors do not imply movement, there is no point trying to argue with you. Try to take on board some basics before you get assertive. PF is about Physics and not about a special MarkoniF's version.

PS please try to stick to one subject at a time. If you want to start arguing about induced currents could you start another thread or resurrect the old (ranting) one?

Until you realise that Vectors do not imply movement, there is no point trying to argue with you. Try to take on board some basics before you get assertive. PF is about Physics and not about a special MarkoniF's version.
I'm not saying vectors generally imply movement, just that in this particular case where we are talking about electromagnetic wave equation "oscillation" of E and B fields indeed refers to their lateral movement.

It is not my version any more than what you say is your special version. I say oscillation vectors are motion vectors and you say it's some force vectors. All I'm asking you now is not to argue but simply point some reference that confirms your version.

Nugatory
Mentor
I'm not saying vectors generally imply movement, just that in this particular case where we are talking about electromagnetic wave equation "oscillation" of E and B fields indeed refers to their lateral movement.
No, there's no lateral movement in this oscillation, just cyclical changes in the strength and direction of the fields.

No, there's no lateral movement in this oscillation, just cyclical changes in the strength and direction of the fields.
Direction of the fields? What does that mean? Direction of what exactly?

- "The electric field is in a vertical plane and the magnetic field in a horizontal plane."

What is it that moves up/down and left/right describing horizontal and vertical planes of E and B fields oscillation if not those fields themselves? And how did you come up with your conclusion, what are you referring to?

Drakkith
Staff Emeritus
Here's my understanding of it.

Take a charged particle and put it in space. Emit an EM wave that will pass over that particle. The electric field will cause the particle to accelerate in a certain direction. The is described by a vector that has a direction AND a magnitude. This vector changes in magnitude over time at the same rate as the frequency of the wave. Once the magnitude of this field rises and falls to zero, it then switches directions and rises and falls again. When it switches the particle is accelerated in the opposite direction as before. The magnitude only describes the strength of the field.

The field itself is not moving. It isn't a physical object and motion can't describe it. What is happening is that the electric and magnetic aspects of the field are changing from one direction to the other in a cyclic fashion. Since a vector is used to describe the EM field, we say the vector is oscillating.

Markonif the picture you linked is NOT a representation of the EM wavefront as it travels. It is only a representation of the field vectors.

Now, I'm no expert, so if that isn't correct then someone please tell me.

Here's my understanding of it.

Take a charged particle and put it in space. Emit an EM wave that will pass over that particle. The electric field will cause the particle to accelerate in a certain direction. The is described by a vector that has a direction AND a magnitude. This vector changes in magnitude over time at the same rate as the frequency of the wave. Once the magnitude of this field rises and falls to zero, it then switches directions and rises and falls again. When it switches the particle is accelerated in the opposite direction as before. The magnitude only describes the strength of the field.
What you are describing is force vector relative to some test charge(s). That can not be since electromagnetic wave equation is derived as propagation E and B fields in vacuum. And even if there were some test charges around the path of the photon that would not make planes of E and B field oscillation perpendicular to the direction of propagation and to each other, it would not make it oscillate all the way along the path. There is nowhere nothing even similar to any of what you describe mentioned in any Wikipedia article, or anywhere else. So how did you come up with all that?

The field itself is not moving. It isn't a physical object and motion can't describe it.
Why so adamant about it, why so sure? Can you quote some reference that even alludes it's not the fields themselves that actually move? What makes you think fields are not physical objects? What else can they be, a dream? Fields can have momentum which makes them quite real, very material and physical things.

What is happening is that the electric and magnetic aspects of the field are changing from one direction to the other in a cyclic fashion. Since a vector is used to describe the EM field, we say the vector is oscillating.
What "aspect" of the field changes direction? Single vector can not describe a field, only force between two fields can be expressed by a vector. Fields are geometrical three-dimensional volumes with potentials, and you only get a vector when you pick one particular point in that field relative to its center of origin.

Look at all the articles in Wikipedia about em waves, or wherever else you want, and see how it's everywhere plainly said it's E and B fields that oscillate. How can you interpret that in any other way but as referring to their motion? How can you assume it's something else when nothing else is mentioned?

Markonif the picture you linked is NOT a representation of the EM wavefront as it travels. It is only a representation of the field vectors.
It is representation of electromagnetic wave equation that describes three-dimensional transverse wave. When you plot that equation you are actually piloting POSITION of E and B fields, not their magnitude or whatever force vectors relative to some test charges, but their position.

http://en.wikipedia.org/wiki/Electromagnetic_wave_equation

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berkeman
Mentor