EM attraction between a solenoid and interstellar hydrogen

AI Thread Summary
The discussion revolves around the interaction between a solenoid acting as an electromagnet and stationary protons. It clarifies that a magnetic field (B field) alone does not exert a force on stationary protons; they require an electric field to induce motion. The participants suggest using an electric field, possibly generated by a Van de Graaff generator, to move the protons and then apply a magnetic field for deflection. There is also a query about the relationship between the distance of protons from the solenoid and the strength of attraction, with references to Coulomb's law and the need for a net charge. The conversation highlights the complexities of electromagnetic interactions and the importance of understanding electric and magnetic fields in this context.
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Okay I have a really odd question that might be difficult to answer. I have searched for an answer in several physics books and websites and don't think I have come across a specific answer for this question.
Suppose I were to send a negative electromagnetic charge through a solenoid and want to attract protons lying along a straight line through the axis of the solenoid. What is the relationship between the charge of the electromagnet and the distance from it to these protons?

This question is not part of any homework or coursework assignments, but rather a component of independent research concerning the feasibility of a time machine.

Any help is greatly appreciated. So far the only candidate I've seen is Coulomb's law but I'm not sure if that's what I need here.

Thanks anyway,
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Are you sending current through the solenoid, turning it into an electromagnet? Or are you just applying a negative voltage to the wires?
 
Well if those protons are at rest they won't feel a force from the B field of the solenoid, they need to be moving. If you want to move those protons you need an electric field and then you could deflect them with a B field. You could make an E field with a parallel plate capacitor setup or a Van de Graaff generator. The only way they would get attracted by the wire of the solenoid is if it had a net charge.
 
Drakkith said:
Are you sending current through the solenoid, turning it into an electromagnet? Or are you just applying a negative voltage to the wires?

Yes, I am sending current through the solenoid and making it an electromagnet.
 
Is it DC current?
 
{?} said:
Yes, I am sending current through the solenoid and making it an electromagnet.

Alright. Just wondering, as I was confused by the term "negative electromagnetic charge" in this context. I think you can just say current. But anyways, I don't think I can help you other than just saying hit up the electromagnet page on wikipedia and have a look around. I know I saw some equations for finding force exerted by the magnet and others there.
 
cragar said:
Is it DC current?
Yeah, I think DC is the only way I would be able to make it function properly.

Drakkith said:
Alright. Just wondering, as I was confused by the term "negative electromagnetic charge" in this context. I think you can just say current. But anyways, I don't think I can help you other than just saying hit up the electromagnet page on wikipedia and have a look around. I know I saw some equations for finding force exerted by the magnet and others there.
Yeah...sorry about my vagueness. I haven't actually taken a formal Physics class ever--just a couple of independent studies with my middle and high-school teachers. So I'm a fair bit behind on my electromagnetic vernacular.
Thanks for your help anyways, guys!

QM
 
there won't be an attraction from the B field of the solenoid to the protons, the protons would have to be moving.
 
The non-uniform magnetic field outside the solenoid will exert a force on the magnetic dipole of the protons even if they don't move.
 
  • #10
ok , are you talking about the Stern–Gerlach experiment.
oh I see F=\nabla (m \cdot B)
 
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  • #11
cragar said:
ok , are you talking about the Stern–Gerlach experiment.
oh I see F=\nabla (m \cdot B)

It's not about the Stern-Gerlach Experiment, I don't think. If I recall correctly, that experiment involved launching particles/atoms through a magnetic field, which led to a deflection in their trajectory. What I'm considering are static protons located at a set distance along the axis of the solenoid. They are not moving through a magnetic field to be deflected; they are static and put into motion (I think) as a result of the EM field.
I have not officially started my vector calculus course, but are you saying that F is a scalar function of B and m? And what exactly do B and m represent? (I've heard a lot of talk about the B field and am highly curious as to what it is)

Like I said--whether or not it makes a difference in the complexity of these replies--I have virtually no quantitative understanding of electromagnetism. I had hoped that this would be a straightforward question, probably as a result of that: If I have a proton twice as far away from the solenoid along its axis as another proton, is the attraction between this further proton and the solenoid four times weaker than the attraction between the solenoid and the nearer proton?

Other, less important questions:
What is the equation relating the attractive force and the distance between the two objects, as well as other quantities/constants which must also be specified?
Do I need a net positive charge on the particles/atoms in order for the EM field to have an effect, or can there exist an attraction between the solenoid and neutral atoms of hydrogen given the correct location?
Is the distance measured from the "center of charge" of the proton and of the solenoid, or is this irrelevant to the calculation? Or is the distance measured from different locations?

I really appreciate anything that you guys can offer in terms of help, but I won't feel insulted if you tell me I'm hosed if I haven't taken a physics E&M course.

QM
 
  • #12
If I were you, I would use an electric field to move the protons, magnetic fields or also called B fields can't do work. Maybe use a van de graaff generator to create an E field.
You can actually calculate some useful stuff using Gauss's law and amperes law, and it just involves algebra for the symmetric cases, solenoid, toroid , sheet current .
http://teacher.pas.rochester.edu/phy122/Lecture_Notes/Chapter31/chapter31.html
this link talks about using amperes law a little bit , And you can use Gauss's law to calculate E fields. At the particle accelerators they use E fields to start the particles moving then deflect them with B fields.
 
  • #13
Okay, I have a different question now concerning the electromagnetic nature of the solenoid: where would the poles be located on a solenoid of length 100km? My guess is that it is at the center of the endpoint of the solenoid but I have a suspicion that this is not exactly true. Any help is greatly appreciated!
QM
 
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