Charged particles under perpendicular magnetic field

Ask questions about projects relating to: aerodynamics or hydrodynamics, astronomy, chemistry, electricity, electronics, physics, or engineering

Moderators: MelissaB, kgudger, Ray Trent, Moderators

Charged particles under perpendicular magnetic field

Postby as005 » Fri Nov 09, 2012 9:34 am

AIM: To observe charged particles under perpendicular magnetic field.

Fellows,

I tried to do an experiment on observing motion of charged particle under influence of perpendicular magnetic field [It should be circular motion due to centrepetal force.] Here is what I did:
1. Dissolved NaCl in Water.
2. Put Zinc Electrodes in the solution dish.
3. Ions started to move in direction of opposite electrodes. Na+ to Anode | Cl- to Cathode. [I only saw creation of ZnCl]
4. I tried to put perpendicular Magnetic field by Bar Magnet.

But All this didn't lead to any amount of circular motion. I am a newbie. Can anyone tell what should I do?

Thanks! :D
as005
 
Posts: 4
Joined: Fri Nov 09, 2012 9:30 am
Occupation: Student: XIIth Grade
Project Question: To observe charged particles under perpendicular magnetic field.
Project Due Date: 20/11/2012
Project Status: I am conducting my experiment

Re: Charged particles under perpendicular magnetic field

Postby John Dreher » Sat Nov 10, 2012 5:35 am

Sorry to be the bearer of bad news, but your idea won't work for numerous reasons. One is that the ions move in the solutions undergoing very frequent collisions that act to randomize their paths. The overall drift is calculated as a biased random walk. Another is that motions of the ions don't produce bulk motion in the fluid, since the mass of the ions is a tiny part of the total mass of the fluid. Yet another is that the radius of curvature of something as massive (more precisely with as high a mass to charge ratio) and slow (compared to the speed of light) as an ion in the kinds of magnetic fields readily available to you is much larger than the size of your test region. And many more. I wouldn't expect any of these effects to be obvious at this point in your studies. I congratulate you on trying an experiment (of any kind) even if it had a null result (that's still a result).

If you want to see the effect of magnetic fields directly, your best bet would be a vacuum tube, in particular something like the CRT (Cathode Ray Tube) that used to be used for the displays in computers and TV sets. If you do try this BE SURE TO GET EXPERT HELP since the high voltages used in these tubes are quite dangerous and the tubes themselves pose an implosion hazard when exposed outside their enclosures. You might be able to see a qualitative effect by bringing a strong permanent magnet near the enclosure of such a tube without disassembling the device (clunky old computer or TV set).
John Dreher
Expert
 
Posts: 294
Joined: Sun Dec 25, 2011 8:33 am
Occupation: Astronomer, Professor of Physics, SETI Researcher (retired)
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable

Re: Charged particles under perpendicular magnetic field

Postby as005 » Sat Nov 10, 2012 6:27 am

I searched for this experiment yesterday, and I came to know that I was trying to use the concept of MHD Propulsion. I came across this video, https://www.youtube.com/watch?v=ciLz_8hDpyw. I am trying to do something like this. As you can see in the video, the fluid moves. But with my experiment, it doesn't. I can't understand what I am doing wrong. Any help would be appreciated! :D
as005
 
Posts: 4
Joined: Fri Nov 09, 2012 9:30 am
Occupation: Student: XIIth Grade
Project Question: To observe charged particles under perpendicular magnetic field.
Project Due Date: 20/11/2012
Project Status: I am conducting my experiment

Re: Charged particles under perpendicular magnetic field

Postby John Dreher » Sat Nov 10, 2012 7:52 am

I'll take a look.
John Dreher
Expert
 
Posts: 294
Joined: Sun Dec 25, 2011 8:33 am
Occupation: Astronomer, Professor of Physics, SETI Researcher (retired)
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable

Re: Charged particles under perpendicular magnetic field

Postby John Dreher » Sat Nov 10, 2012 9:56 am

electromagnet.pdf
Now _that's_ a _magnet_!
(82.88 KiB) Downloaded 86 times
Looks like mud on my face! I seem to be way out of date on what kind of magnetic fields these neodymium magnets produce. When I studied EM theory, an 0.6 tesla magnet, as used in one of the videos that actually gave numbers for the relevant magnetic fields and currents, needed a magnet as big as a room!! (I've attached a picture.) With this kind of field you can indeed get a little movement.

What is going on is not a direct spiral motion of the ions, but a statistical bias in the collective motions induced by the current and by the magnetic field acting in tandem. In free space the voltage applied along one axis would exert a force on a charged particle which would cause it to accelerate in the direction of the electric field (if it is a positively charged ion). The magnetic field, however, would deflect the motion into a circular motion around the magnetic field line. For an ion in solution, however, the ion will be jiggling around due to thermal motions; when exposed to an electric field it will pick up an extra velocity component adding to its motion along the direction of the field, but it will smash into a solute molecule in about 0.01 nanoseconds and bounce off in a random direction. The extra component of velocity is very small compared to the thermal motions, but it creates a bias in the collisions that will add up into a small drift of the fluid in the direction of the field. Calculating how much drift looks to me to be fairly complicated. (If you are interested I can point out some of the considerations needed to make this calculation.)

You say you are using a bar magnet. I don't think that will be optimal to produce a uniform magnetic field that points in one direction over an appreciable test volume. Also, you must use one of these (relatively) new neodymium magnets in order to get a magnetic field large enough to see anything. The demo probably had a small, 1 inch neodymium disc magnet under the cup. The ideal configuration for very high fields would, I think, be two axially polarized ring magnets with a central bore of about 1 inch placed one above the other with a separation of about 2 inches to give you a small (~1 cubic inch) working area and a VERY large field. Here is a reference to the kind of magnets I am thinking of

http://www.kjmagnetics.com/proddetail.asp?prod=RY0X04

I'd guess you'd get a field of ~2 T [my eyes pop out in amazement]. You will need a very sturdy frame to hold the magnets, made of wood or aluminum or some other strong, non-ferrous material. Be sure to epoxy the magnets into place so they can't escape their supports.

The fluid used should be as conductive as possible. For salt water, be sure to get as much salt as possible into, perhaps by boiling the water and a pile of salt briefly, then filtering out the remaining salt in the cooled solution.

********If you start to work with powerful neodymium magnets be extremely careful of your fingers, they can literally be cut off or smashed to pulp by magnets like these snapping together (the magnet rig mentioned above would exert a force of a hundred pounds or so between the magnets and much more as the distance between the magnets decreases). Also, wear eye protection, since these magnets are brittle and if something snaps onto one chips could fly at high velocity. Adult supervision IS MANDATORY.***********
Last edited by John Dreher on Sat Nov 10, 2012 1:06 pm, edited 1 time in total.
John Dreher
Expert
 
Posts: 294
Joined: Sun Dec 25, 2011 8:33 am
Occupation: Astronomer, Professor of Physics, SETI Researcher (retired)
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable

Re: Charged particles under perpendicular magnetic field

Postby as005 » Sat Nov 10, 2012 11:33 am

Haha, Technology is changing kind of fast now-a-days. Someone rightly said, Chaos will reign.

BTW I just wanted to ask one more question. Is there anyway to do the experiment without neodymium magnets? Can I do it with some sort of electro-magnet? Or will a horse-shoe magnet work?

And when you said that fluid should be conductive, what did you exactly mean? I thought normal salt-water solution was fairly conductive. :/

Thanks for all the help!!! :D
as005
 
Posts: 4
Joined: Fri Nov 09, 2012 9:30 am
Occupation: Student: XIIth Grade
Project Question: To observe charged particles under perpendicular magnetic field.
Project Due Date: 20/11/2012
Project Status: I am conducting my experiment

Re: Charged particles under perpendicular magnetic field

Postby John Dreher » Sat Nov 10, 2012 1:17 pm

Re: magnet. Yes you need a neodymium magnet. The small ones, e.g. 1" disc, are fairly cheap (i.e. < shipping). The picture I just now attached to my previous post shows what a 1T class electromagnet looks like. Toy horseshoe magnets are 1000 times weaker than neodymium magnets.

Re: conducting fluid. Yes, salt water is conductive. The saltier, the better -- hence my comment about ensuring a saturated solution of salt. Just stirring in salt to cold water does not usually result in a fully saturated solution. Sulfuric acid or HCl is even better, but nasty to work with and corrodes the electrodes rapidly. Makes poison gas too. Yummy :(
John Dreher
Expert
 
Posts: 294
Joined: Sun Dec 25, 2011 8:33 am
Occupation: Astronomer, Professor of Physics, SETI Researcher (retired)
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable

Re: Charged particles under perpendicular magnetic field

Postby as005 » Sun Nov 11, 2012 7:04 am

Thanks for all the help Sir. Really appreciate it. :)
as005
 
Posts: 4
Joined: Fri Nov 09, 2012 9:30 am
Occupation: Student: XIIth Grade
Project Question: To observe charged particles under perpendicular magnetic field.
Project Due Date: 20/11/2012
Project Status: I am conducting my experiment


Return to Grades 9-12: Physical Science

Who is online

Users browsing this forum: Bing [Bot] and 2 guests