What is the purpose of having a magnetic field?

[k9b4]

What does a magnetic field do? I understand that we create the idea of an electric field to more easily explain why electric charges attract and repel each other, but what is the purpose of having a magnetic field?

 

[Matterwave]

The magnetic field is as necessary to explain the motion of charges just as much as the electric field is.

 

[k9b4]

The magnetic field is as necessary to explain the motion of charges just as much as the electric field is.

Why?

 

[Matterwave]

Why?

The electric field only gives you the forces between charges which are static. Once the charges start to move, they will see magnetic fields come into play and require both the electric field and magnetic field to figure out their motion.

This is a pretty broad field, so maybe look here first: http://en.wikipedia.org/wiki/Magnetic_field

 

[k9b4]

The electric field only gives you the forces between charges which are static. Once the charges start to move, they will see magnetic fields come into play and require both the electric field and magnetic field to figure out their motion.

This is a pretty broad field, so maybe look here first: http://en.wikipedia.org/wiki/Magnetic_field

Does a magnetic field cause charged particles to move?

 

[Matterwave]

Does a magnetic field cause charged particles to move?

A static magnetic field won't cause a static charge to move, but it will change its direction of motion once it does start moving.

The full force law considering both electric and magnetic fields is the Lorentz force law:

$$\vec{F}=q(\vec{E}+\vec{v}\times\vec{B})$$

 

[k9b4]

A static magnetic field won't cause a static charge to move, but it will change its direction of motion once it does start moving.

The full force law considering both electric and magnetic fields is the Lorentz force law:

$$\vec{F}=q(\vec{E}+\vec{v}\times\vec{B})$$

Why does a magnetic field only affect charged particles when the magnetic field is moving? A static electric field created by a charged particle will attract or repel other charged particles.

 

[Nugatory]

Does a magnetic field cause charged particles to move?

A charged particle moving in a magnetic field experiences a force that is perpendicular to the direction of motion and proportional to its speed. If the particle is not moving, the speed and therefore the magnetic force are zero. If anything starts the particle moving there will be a non-zero force from the magnetic field, as well as the force from the electrical field.

 

[Matterwave]

Why does a magnetic field only affect charged particles when the magnetic field is moving? A static electric field created by a charged particle will attract or repel other charged particles.

That's just the way things are. The magnetic field has to do with charges in motion. It is different from the electric field, because it's not the electric field. There are a whole lot of intricacies in this, and the motion of charges in electric and magnetic fields is a very wide area of study (basically all of electro-magnetic theory), so I would suggest you read up on it, perhaps first through the wikipedia page, or from some online resources, or from your E&M textbook.

 

[Dale]

Why does a magnetic field only affect charged particles when the magnetic field is moving?

This is just a little nitpick, but the magnetic field only affects charged particles when the charged particles are moving. The magnetic field itself doesn't have a velocity, although changes in the electromagnetic field do.

 

[k9b4]

But what is a magnetic field? I understand that electric fields do not physically exist, and that you can imagine how charges will interact with each other without thinking of an electric field at all. The negative electron repels other negative electrons and when you oscillate the electron up and down it causes other electrons to move up and down because the electron is changing position and pushing other electrons around. What does a magnetic field do and how can I imagine what it does without imagining that a magnetic field is there at all?

Unless my way of viewing charge interaction without an electric field is wrong?

 

[Drakkith]

Unfortunately there really isn't an easy way to visualize a magnetic field like you can the electric field since the magnetic field acts sort of indirectly on charged particles. It is only when they are moving or when the magnetic field is changing that a particle will respond to it, and even then the particle doesn't respond in a direct sort of way, instead responding by moving in directions perpendicular to the direction of the field lines.

You may have to settle for simply not being able to visualize charge interaction without using a magnetic field.

 

[Drakkith]

Also, you need to understand that the entire concept of a "field" is a mathematical and conceptual way to make sense of how particles interact. Fields are used extensively in physics because they offer what is probably the simplest way of understanding much of the fundamental interactions of nature. They are so useful that entire theories have been developed to describe even particles in terms of an underlying field. (See the various Quantum Field Theories)

Trying to understand how particles interact without understanding the field that describes their interaction is not going to get you anywhere.

 

[k9b4]

Also, you need to understand that the entire concept of a "field" is a mathematical and conceptual way to make sense of how particles interact. Fields are used extensively in physics because they offer what is probably the simplest way of understanding much of the fundamental interactions of nature. They are so useful that entire theories have been developed to describe even particles in terms of an underlying field. (See the various Quantum Field Theories)

Trying to understand how particles interact without understanding the field that describes their interaction is not going to get you anywhere.

But I like to think about what is actually there. A field is not actually there. An electron however, has a mass and exists in reality.

 

[Mark44]

k9b4, you've asked a lot of "why" questions. Here's a video of Richard Feynman on magnetism and "why" questions and how difficult they are - http://www.bing.com/videos/search?q...&mid=EBC66564088F7695161DEBC66564088F7695161D.

 

[k9b4]

k9b4, you've asked a lot of "why" questions. Here's a video of Richard Feynman on magnetism and "why" questions and how difficult they are - http://www.bing.com/videos/search?q=Feynman Magnets&Form=VQFRVP#view=detail&mid=EBC66564088F7695161DEBC66564088F7695161D.

Just because my questions might be difficult to answer, doesn't mean that they don't have an answer.

 

[Mark44]

Just because my questions might be difficult to answer, doesn't mean that they don't have an answer.

Feynman's point is that the person asking "why" might not have enough background knowledge to understand the answer.

 

[k9b4]

Feynman's point is that the person asking "why" might not have enough background knowledge to understand the answer.

But I'm asking for an intuitive answer, not a mathematical one. "I don't know" is a perfectly acceptable answer.

 

[Drakkith]

But I like to think about what is actually there. A field is not actually there. An electron however, has a mass and exists in reality.

How do you know the field isn't actually there? Keep in mind that a particle is no less mathematical or conceptual than a field is. And if the field isn't there, what happens to the energy lost from radiating particles before the radiation is absorbed by another particle? Is that energy simply gone? If the field doesn't exist, then why do field theories have such success over purely particle theories?

A field allows us to answer questions like this by treating the field as an actual entity and not just clever math. (of course one could argue that all math is "clever math" if it enables us to accurately describe reality, whether or not that math is for particles or fields)

 

[Drakkith]

But I'm asking for an intuitive answer, not a mathematical one. "I don't know" is a perfectly acceptable answer.

There aren't always intuitive answers. Sometimes reality simply doesn't match up with our intuition. The key is to realize that intuition isn't something that is set in stone, but is something that can be molded as you learn more. Many things that don't make sense to you now will probably be absolutely obvious in the future.

 

[k9b4]

How do you know the field isn't actually there? Keep in mind that a particle is no less mathematical or conceptual than a field is. And if the field isn't there, what happens to the energy lost from radiating particles before the radiation is absorbed by another particle? Is that energy simply gone? If the field doesn't exist, then why do field theories have such success over purely particle theories?

A field allows us to answer questions like this by treating the field as an actual entity and not just clever math. (of course one could argue that all math is "clever math" if it enables us to accurately describe reality, whether or not that math is for particles or fields)

A field doesn't exist in the sense that it has no mass. I am using the word "exist" to mean "has mass". Therefore, something with no mass does not exist. Energy is another thing which does not exist according to this definition. I agree that both energy and fields are useful concepts to help understand how things work, but both do not possesses mass and are "not actually there".

There aren't always intuitive answers. Sometimes reality simply doesn't match up with our intuition. The key is to realize that intuition isn't something that is set in stone, but is something that can be molded as you learn more. Many things that don't make sense to you now will probably be absolutely obvious in the future.

I don't believe there aren't always intuitive answers. I believe that lack of an intuitive answer simply means that no one fully understands what's going on yet.

 

[Mark44]

How do you know the field isn't actually there? Keep in mind that a particle is no less mathematical or conceptual than a field is. And if the field isn't there, what happens to the energy lost from radiating particles before the radiation is absorbed by another particle? Is that energy simply gone? If the field doesn't exist, then why do field theories have such success over purely particle theories?
A field allows us to answer questions like this by treating the field as an actual entity and not just clever math. (of course one could argue that all math is "clever math" if it enables us to accurately describe reality, whether or not that math is for particles or fields)

A field doesn't exist in the sense that it has no mass. I am using the word "exist" to mean "has mass". Therefore, something with no mass does not exist. Energy is another thing which does not exist according to this definition. I agree that both energy and fields are useful concepts to help understand how things work, but both do not possesses mass and are "not actually there".

Your definition of existence is oversimplistic. By your definition, light and other electromagnetic radiation don't exist (because photons don't have mass) nor do neutrinos. If these things don't exist, how do you account for the fact that we can detect light with our eyes, and we can detect neutrinos by their (rare) interactions with other atoms.

There aren't always intuitive answers. Sometimes reality simply doesn't match up with our intuition. The key is to realize that intuition isn't something that is set in stone, but is something that can be molded as you learn more. Many things that don't make sense to you now will probably be absolutely obvious in the future.

I don't believe there aren't always intuitive answers. I believe that lack of an intuitive answer simply means that no one fully understands what's going on yet.

I disagree. Just because no one has yet come up with an answer that a layman could understand doesn't mean that a concept isn't well understood.

Did you watch the Feynman video? It was directly related to the questions you're asking.

 

[k9b4]

Your definition of existence is oversimplistic. By your definition, light and other electromagnetic radiation don't exist (because photons don't have mass) nor do neutrinos. If these things don't exist, how do you account for the fact that we can detect light with our eyes, and we can detect neutrinos by their (rare) interactions with other atoms.

Yes exactly. Electromagnetic waves do not exist because electromagnetic waves are electromagnetic fields, which do not exist. Our seeing of light can be explained simply by oscillating charges causing electrons in our eyes to oscillate which sends electric signals to our brains which we perceive as light. No electromagnetic fields/waves need come into the picture.

I disagree. Just because no one has yet come up with an answer that a layman could understand doesn't mean that a concept isn't well understood.

Did you watch the Feynman video? It was directly related to the questions you're asking.

Yes I watched the Feynman video. He was saying that It's difficult to communicate difficult concepts to laymen because they lack background knowledge required right? I was under the impression that the background knowledge he was referring to was purely mathematical.

 

[Nugatory]

Electromagnetic waves do not exist because electromagnetic waves are electromagnetic fields, which do not exist. Our seeing of light can be explained simply by oscillating charges causing electrons in our eyes to oscillate which sends electric signals to our brains which we perceive as light. No electromagnetic fields/waves need come into the picture.

And how does an oscillating charge in the location where the light is emitted affect the oscillation of an electron in your eye? Something exists that allows the the one oscillation to cause the other, and we call that something an electromagnetic field.

 

[Evo]

Closed pending moderation.

 

[Nugatory]

Time to lock this thread. The original question has been answered, and the subsequent discussion has veered far away from mainstream science.