Challenge Questions Blog

Challenge Questions

Stop in and exercise your brain. Talk about this month's Challenge from Specs & Techs or similar puzzles.

So do you have a Challenge Question that could stump the community? Then submit the question with the "correct" answer and we'll post it. If it's really good, we may even roll it up to Specs & Techs. You'll be famous!

Answers to Challenge Questions appear by the last Tuesday of the month.

Previous in Blog: Accelerating Spaceship: Newsletter Challenge (07/01/11)   Next in Blog: The Floating Superconductor: Newsletter Challenge (September 2011)
Close
Close
Close
36 comments

Magnetic Monopole: Newsletter Challenge (August 2011)

Posted July 31, 2011 5:01 PM

This month's Challenge Question:

Americium-241 is a good alpha emitter. If you isolate a gram of Americium-241, it emits alpha particles in all directions. An alpha particle is a positive charge because it consists of two protons and two neutrons bound together. The emission of alpha particles by the gram of Americium-241 produces lines of current radiating from the center of the source. Each line of current generates a magnetic field. The source, then, is a magnetic monopole. How can this be?

And the Answer is:

Magnetic monopoles do not exist (today). The each current line radiating outward from the center of the source (Americium-241) produces a magnetic field; However, the field from each current line is canceled by the fields from the other rays. (Use the right-hand rule to convince yourself)

Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
2
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#1

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

07/31/2011 8:09 PM

Loosely put, the alpha particle is not a magnetic monopole, just a charged particle with a +2e charge.

The Americium-241 is also not a magnetic particle. However, the decay causes charged particles to be emitted from an central source (Americium-241 atom). It may give the illusion that the atom is a monopole, but it isn't.

Reply Good Answer (Score 2)
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#2

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/01/2011 5:16 AM

When the alpha particle takes the +2e charge away from the nucleus, there are 2 too many electrons in the resulting atom. I'd guess that these have to go somewhere, and when they do, they'll generate a magnetic field opposing that caused by the alphas.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#3
In reply to #2

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/01/2011 6:23 AM

I think that is the Beta decay portion when the electrons scoot off.

Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#4
In reply to #3

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/01/2011 6:40 AM

No - beta decay is a nuclear event. A neutron changes into a proton and electron (beta particle) and an electron antineutrino.

I'm thinking of the superfluous 'atomic' electrons.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply Score 1 for Good Answer
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#5
In reply to #4

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/01/2011 7:57 AM

Ah, you are right.

Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Hearts of Oak Popular Science - Paleontology - New Member Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2005
Location: In the Garden
Posts: 3390
Good Answers: 75
#6

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/01/2011 8:08 AM

Well.... if the 2 "surplus" electrons are pootling off away from the small heap of Americum-241 (suspended magically in mid air I assume if the alpha particles are truely pottering off in all directions), then the electrical current is flowing into the pile of A-241...since current direction is opposed to electron movement.

Moving charges...doesn't movement+charge+flux = magic triangle where if you have two, the third appears? Motors produce motion when you add current to magnetic field, dynamos produce current when you add motion to magnetic field...here we have movement and current -> magnetic field?

All this subject to JDG and AH's pertinent observations. I'm going for the published answer....

Further thought: does the movement of +2e alpha particles produce a negative current???

__________________
Chaos always wins because it's better organised.
Reply
Guru

Join Date: Aug 2007
Location: London England.
Posts: 583
Good Answers: 10
#21
In reply to #6

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 2:51 PM

Damn,I was going to say that!

__________________
When I die I'd like to go peacefully in my sleep like my dad,not shouting and screaming like his passengers.
Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#7

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/01/2011 9:58 AM

Another thought (ER's post made me think dammit!) - any mag. field produced by the moving charges will be perpendicular to the direction of travel - so they can't 'leave a monopole behind' at the Np-237 nucleus.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply
Guru
United Kingdom - Member - Hearts of Oak Popular Science - Paleontology - New Member Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2005
Location: In the Garden
Posts: 3390
Good Answers: 75
#8
In reply to #7

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 3:40 AM

<smug smile> My day is complete

I meant to mention about the magnetic lines being perpendicular...now: can someone explain what a magnetic monopole is, please?

If the current lines are radial, doesn't that make the mag. field lines concentric to the pile of A-241/NP-237, giving the impression of a point source for the mag. field?

I am but a simple clanky...

__________________
Chaos always wins because it's better organised.
Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#9
In reply to #8

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 5:26 AM

The magnetic filed lines due to each alpha would be like this:

... so the combined field would be some kind of spherical thing (IMHO it would cancel itself out).

A magnetic monopole (if it existed) would have the field lines radiating from the pole.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#10
In reply to #9

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 7:21 AM

Not exactly, more like a cylinder. Imagine an infinitely long wire carrying DC current in a vertical direction. Using the right hand rule, with your thumb pointing up, the magnetic lines of force vector in concentric circles in the direction of your curled fingers. Much like your drawing.

If you move a mechanical compass next to the wire the compass will orient itself parallel with the lines of force. The polarity in the example I cited is such that the north pole of the compass points in the same direction that your curled fingers point.

This page illustrates the point.

Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#11
In reply to #10

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 7:48 AM

The field for each alpha would be cylindrical - I'm referring to the combined field from all the radiating alphas. Kinda like a lot of cylinders with their axes meeting at a point.

As the field from two adjacent alphas (cf two adjacent current-carrying conductors) combine to form a larger (elliptical) cylinder, the combined fields from all the radiating alphas would be like spherical shells. Ish .

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Hearts of Oak Popular Science - Paleontology - New Member Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2005
Location: In the Garden
Posts: 3390
Good Answers: 75
#12
In reply to #11

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 7:57 AM

Thank you both...that's clearer...I thunk...

__________________
Chaos always wins because it's better organised.
Reply
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#13
In reply to #11

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 8:28 AM

The alpha particles are not coming from a point source, but a mass of atoms, therefor they are just a colony of atoms.

This is one reason the idea of spontaneous alpha emission is not a true monopole, because americium-241 decays only once, then become neptunium-237 and it is done for quite a while.

The half-life for 237np is something like 200,000 years compared to 241am, which is about 400 years.

So, the effect is temporary and spontaneous as far as a true point source goes. However, pack enough radioactive material together and it will appear to be a point source to our eyes, so to speak, but it really is not.

Much like a galaxy looks like a point-source star to the naked eye, but when resolved in a high power telescope you begin to see the individual members and it is clear it is not a point.

Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#14
In reply to #13

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 9:43 AM

Agreed, but in practical terms (where we check 'lines of magnetic field' with a compass needle, or by iron filings scattered on a sheet of paper) a 'blob' of Am-241 could be considered a point source of alphas.

For instance, the amount of Am-241 in a smoke detector (if Wikipedia is to be believed and if my sums are correct) could be contained in a sphere of radius 0.027mm. Pretty much a point source on the macro scale.

This blob would be squirting out about 37,000 alphas per second.

Edit - and how much of a "point" does it need to be? Even an atomic nucleus is not a point in the mathematical sense.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply
Guru

Join Date: Mar 2009
Posts: 507
#28
In reply to #9

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/03/2011 12:14 AM

each alpha emission changes the direction of the magnetic field

Reply Score 1 for Off Topic
Guru
Popular Science - Cosmology - Let's keep knowledge expanding Engineering Fields - Retired Engineers / Mentors -

Join Date: Dec 2006
Location: North America, Earth
Posts: 4384
Good Answers: 104
#26
In reply to #8

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 7:27 PM

Magnetic monopoles are hypothetical particles proposed by Paul Dirac that carry a single magnetic pole, either a magnetic north pole or south pole.
They have now been observed. here too

__________________
“I would rather have questions that can't be answered than answers that can't be questioned.” - Richard Feynman
Reply
Guru
Popular Science - Cosmology - New Member Engineering Fields - Civil Engineering - New Member Engineering Fields - Nuclear Engineering - New Member United States - Member - New Member

Join Date: Aug 2010
Posts: 714
Good Answers: 37
#31
In reply to #26

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/03/2011 10:08 AM

Great links!

It's been some time since I took physics so I might be wrong or I might be asking the wrong questions here. As I recall, the foundation for most of our electrical theory (Maxwell's stuff) is based on that monopoles do not exist but only dipoles. I realize that for practical purposes and problems that are in electrical in natural those equations work great.

Doesn't the existence of monopoles have far reaching implications with regard to these fundamental equations? i.e. won't a new set of equations be formulated? Or is this just another case of what works at one scale doesn't apply in another?

__________________
Sometimes my thoughts are in a degree of order so high even I don't get it...
Reply
Participant

Join Date: Aug 2011
Posts: 1
#15

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 10:28 AM

There would be a little magnetic loop for each particle as it emits, traveling with it. If there were a lot of particles emitted simultaneously (all at the same radius), the loops would just cancel each other out. A steady, close-set stream of particles on each radian would also have cancelling loops (or magnetic cylinders). However, with a 400(?) year half-life and only a gram, and the speed at which the particles radiate, I suspect that most of the space and time even "near" the lump is only sparsely populated with alphas. (By "near", I mean just far enough away for it to appear a point in relation to the field of observation, as opposed to "immediately adjacent", where the lump appears a sphere or even a plane). In this sparse case, the magnetic field is only temporally ephemeral sparks and streaks in random directions, each so feeble it is not sensible beyond the immediate vicinity of its generating particle.

Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#16
In reply to #15

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 10:38 AM

"... only a gram..." !

Am-241 has a specific activity of over 3Ci/g, so one gram of the pure substance would produce over 1 x 1011 alphas per second (reducing to 5 x 1010 after 400 years).

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply
Member

Join Date: May 2011
Location: River Falls, WI
Posts: 7
#17

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 10:45 AM

The magnetic monopole illusion of Americium-241 is by a by-product from alpha decay. The lines of current that are formed in electromagnetic pulses/waves when the ejected alpha particles become ionized. The alpha particles that are ejected, extend from the the isolated gram of Americium-241 only a short distance in all directions until they are also balanced by the nuclear force present. The electromagnetic force of the protons will continue to work over time to pull the neutrons further away into higher orbits from the unstable nucleus. With help of the next wave/emission of alpha particles from Americium-241 these electromagnetic forces will continue to expand outward during alpha decay until the supporting atomic structure can no longer hold them in orbit or lost completely once the resulting nucleus decays to its next stable state.

__________________
Viva la Theorem X!
Reply
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#18
In reply to #17

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 12:12 PM

Welcome to CR4!

I think any alpha particles that are emitted are not necessarily recaptured by the parent atom.

I can see other neighboring atoms absorbing the alpha particle, but once it leaves the mass of 241am it will keep going at about 15,000 km/s until it strikes something else.

Also, if I understand it correctly, 241am decays to 237np once the alpha particle is ejected. 237np will further decay with an alpha particle to something like 209bi, but 237np is pretty stable and it takes much longer (statistically) before that happens.

Reply
Member

Join Date: May 2011
Location: River Falls, WI
Posts: 7
#19
In reply to #18

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 1:03 PM

If that was the case... How would the illusion be apparent? I would imagine that since it takes so long to decay to being with the outer shell of the parent atom would be expanding in an organized magnetic-geodesic configuration based upon the structure of the parent and extend until that outer layer/shell is semi stable until it is further pushed out forcing the release of the alpha particles from orbit. Its new the layers in orbit bumping into one another (in a pulsing fashion) as they grow outward that creates the wave pulse. If they are ejected and never slow we could never observe this illusion.

__________________
Viva la Theorem X!
Reply
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#20
In reply to #19

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 2:10 PM

You wrote, "If that was the case... How would the illusion be apparent?"

Because the challenge question is purposely nebulous. There is a difference between one atom emitting an alpha particle and a mass of 241am where a significant number of atoms make up that mass.

On average, one atom of 241am has a 50% probability of decaying in about 400 years! That is only one alpha emission.

When it does the resulting atom is now neptunium-237. That atom has a 50% probability of decaying to bismuth in about 200,000 years.

My understanding of nuclear physics is that when an alpha particle is emitted it doesn't stop and shop around in or near the electron shells, it pops out from the nucleus and keeps going.

Remember, the nuclear force is a strong force (that which holds a nucleus together or binding force), but it has a very, very limited distance it operates on.

The force that holds electrons in their shells is from the charge attraction between protons and electrons.

Reply
Member

Join Date: May 2011
Location: River Falls, WI
Posts: 7
#22
In reply to #20

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 2:53 PM

My bad, I thought we were talking about 1 gram of 241am. One atom decaying alone like you describe will be different of course than the observed decay of a 1 gram chunk of the element. Then wouldn't the resulting mass of the element have a greater nuclear force? Thus allowing the shopping effect. Just trying to think big here... I'm running off instinct, there's no denying that

__________________
Viva la Theorem X!
Reply
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#23
In reply to #22

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 4:04 PM

Not to my knowledge of nuclear physics. The alpha particle shoots off at about 5% the speed of light, so it not Sunday driving, but it's no gamma ray, either. ;-)

I do know that it doesn't take much to stop an alpha particle. Just a few layers of epithelia skin cells will do it. Any emission inside the chunk would have a harder time surfacing.

Reply
Member

Join Date: May 2011
Location: River Falls, WI
Posts: 7
#25
In reply to #23

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 4:07 PM

Emissions within are present in this case, I would assume...

__________________
Viva la Theorem X!
Reply
Power-User
Popular Science - Weaponology - New Member

Join Date: Jun 2011
Location: Berkeley, CA USA
Posts: 128
Good Answers: 4
#24
In reply to #22

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 4:07 PM

If you are curious about energies involved you may look here

http://atom.kaeri.re.kr/ton/nuc6.html

where you will find

  • Spin: 5/2-
  • Half life: 432.2 years
  • Mode of decay: Alpha to Np-237
    • Decay energy: 5.638 MeV

So the Alpha exits with ~5.6MeV. That is a LOT of energy. MeV and it only takes 54.4eV to fully ionize He to an Alpha particle. So until the Alpha dissipates it's energy from >5MeV down to < 54eV it will remain fully ionized. I have not calculated the 1st ionization energy for He.

__________________
Working to end the use of carbon for energy
Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 20983
Good Answers: 781
#27

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/02/2011 11:47 PM

What occurs at the other end of the spaghetti: an opposite monopole? If so, how does this really differ from declaring that an ordinary bar magnet consists of a north monopole at one end and a south at the other?

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
Good Answers: 467
#29
In reply to #27

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/03/2011 4:42 AM

I was wondering the same thing.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply
Power-User

Join Date: Jun 2007
Location: Madras, India
Posts: 174
Good Answers: 8
#30

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/03/2011 5:01 AM

My impression of a magnetic monopole is one from which magnetic "lines of force" (whatever that may mean) emanate radially outward from the pole, presumably represented by a point, and presumably having the same concentration or intensity in all possible directions, without ever terminating on another opposite pole.

Others have already pointed out that an alpha particle emitted from a nucleus in the source is equivalent to a current flowing in a radially oriented conductor, and the magnetic lines of force for a single such current are concentric circles in a "plane" perpendicular to the radius. As far as I can see (which may not be very far*) there should be no net magnetic field in any radial direction.

If we consider two alpha particles emitted simultaneously with equal speed at some acute angle to each other, then along the bisector the magnetic field should cancel out completely. At any other point I would expect a transitory resultant which may have net outward or inward components (?). With a regular stream of alpha particles, any point in the surrounding space lies potentially on such a bisector, and there should be no net magnetic force when averaged over space and time, though there will surely be temporary local fluctuations. I doubt whether that would qualify for the label of monopole.

I think JohnDG has said essentially the same thing (#9) in response to ER (#8). People who are conversant with vector calculus and statistical procedures can judge whether my purely qualitative observations have any merit.

* I readily admit to having left nearly all my physics behind at college over forty years ago, but I stumbled on this challenge, and ventured to put in my tuppence worth. I'd appreciate any critique of faults in my reasoning. Thanks. =TeeSquare=

Reply
Guru
United Kingdom - Member - Hearts of Oak Popular Science - Paleontology - New Member Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2005
Location: In the Garden
Posts: 3390
Good Answers: 75
#32
In reply to #30

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/03/2011 6:24 PM

Clear explanation - and nice to see you and StandardsGuy are still around

__________________
Chaos always wins because it's better organised.
Reply
Power-User

Join Date: Jun 2007
Location: Madras, India
Posts: 174
Good Answers: 8
#33
In reply to #32

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/03/2011 9:13 PM

Thanks for your comments. I was actually hoping someone knowledgeable would make critical remarks. I had indeed dropped out of the CR4 circuit over a year back when I noticed some changes in the way it was being administered, and also that FYZ and Kris (who had persuaded me to upgrade from guest status) seemed to have moved on perhaps to greener pastures. Anyway I continue to be terrified of the internet and all things related to computers, though I did manage to keep up some exchanges in this forum for a while. My grouse was that many of my carefully thought-out posts elicited little or no comment. Perhaps that is to be expected in public forums and blogs -- unfamiliar and confusing territory for me really. It could be that my responses were too slow as I use internet only briefly, and prefer to read and edit while off-line. The few GAs I earned were more for silly verses and limericks or off-topic stuff! But I must admit that there were a lot of interesting challenges and discussions, and I learnt a great deal from many of them, and quite honestly I did get quite a few very positive responses to the technical content in my posts.

I have seen some of your posts before, and recall enjoying some of the exchanges and related banter! Thanks again, =TeeSquare=

Reply Off Topic (Score 5)
Guru
United Kingdom - Member - Hearts of Oak Popular Science - Paleontology - New Member Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2005
Location: In the Garden
Posts: 3390
Good Answers: 75
#34
In reply to #33

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/04/2011 3:48 AM

My input to the boards decreased whilst I was playing in the Bath...then I got out of there and often only read my PMs. Kris is still around, but I think he probably spends less time on the boards. PM list has gone quiet, so I've sneaked out to play!

__________________
Chaos always wins because it's better organised.
Reply Off Topic (Score 5)
Power-User

Join Date: May 2011
Location: Chapel Hill, NC (sometimes Otago NZ)
Posts: 120
Good Answers: 1
#35

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/09/2011 11:24 AM

I agree with the geometric intuition that says all the radially circulating B-fields should net cancel but there is a deeper problem here. One has to remember that one can get into trouble when converting granular things into continuum descriptions and idealizing a body as a point object but let us just accept that for the moment. For argument we assume a uniform constant outwards positive current flux from a point source.

One of the self consistency conditions of Maxwell's equations is that divJ=0. This follows from Ampere's law and div(curl B)=0. The very assumption leads to inconsistency unless you are careful to reduce the central charge appropriately. This is easy to miss if we are treating the whole blob of material as the "pointlike" source. You may be able to massage magnetic monopole from it but I think it is in the same class as the "1=0" proofs that rely on hidden division by zero. (A single inconsistency makes everything true.)

As a last ditch attempt to give meaning to this problem, assume that the spins of the emitted particles are parallel to the direction of motion. In the continuum picture this gives a north end traveling outwards with the alpha particle front and a south end bound at the nucleus. This is still inconsistent. Imagine an annulus with its outside surface north and inside south. The flux lines can't reconnect so it is still inconsistent with Maxwell's equations (even the ones that allow magnetic charges). Granularity saves us. The north and south pole of the dipole's travel outwards with the particles as localized dipoles.

Reply
Active Contributor

Join Date: Aug 2011
Posts: 13
#36

Re: Magnetic Monopole: Newsletter Challenge (August 2011)

08/10/2011 6:57 PM

There is no magnetic monopole created.

Here is a quick mental check: which pole do you suppose would be created in such a situation north or south? How could there be a preference for either one; the magnetic field about a single alpha particle is completely rotationally symmetric about the line of travel?

If one now supposes a whole lot of alpha particles (enough to integrate over the spherical space) coming off with spherical symmetry, then everywhere that one particle causes a north pole another will cause an equal strength south, so there will be no net magnetic field at all.

What is being created is a negative electric monopole -- until the electrons have a chance to neutralize it.

Reply Score 1 for Good Answer
Reply to Blog Entry 36 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

ALogicalSenseOfReason (4); Anonymous Hero (8); Bazzer Englander (1); cchaf (1); ChaoticIntellect (1); English Rose (5); JohnDG (8); regsoft (1); StandardsGuy (1); TeeSquare (2); Tornado (1); tsaravich (1); vauko (1); WilhelmHKoen (1)

Previous in Blog: Accelerating Spaceship: Newsletter Challenge (07/01/11)   Next in Blog: The Floating Superconductor: Newsletter Challenge (September 2011)

Advertisement