Dear colleagues,
We are conducting experiments on battery-magnet systems running in copper tube (also known as World's Simplest Electric Train). Our equipments includes:
-A pin size AAA or AA buy from duracell or engyzer company, voltage 1.5 V.
-Two Neodymium magnets are larger than batteries.
- An uncoated copper coil, 54 rounds / 1.5 dm, larger diameter than the battery, straight.
Attach two magnets to both ends of the battery and push it into the copper tube. The copper tube vibrates but the battery moves only a few millimeters and stops.
I hope the experts help me to make the battery move in the coil like video:
https://www.youtube.com/watch?v=aTnK1gl_yag
I look forward to hearing from you soon.
Thank you very much.
Dear Nguyen, please pay attention to three points:
- The inner diameter of the coil has to be larger (about 1 mm is o.k.) than the outer diameter of the magnets in order to let the battery-magnets-assembly move freely.
- The battery should not be electrically shorted by the magnet at the positive pole, and the coil must not be shorted by the battery (e. g. if the paint layer on the battery is defect). If you are not sure you could cover the battery (except their contacts, of course) by a piece of shrinking tube.
- The polarization of the magnets should point in opposite directions. So, one magnet is drawn into the field caused by the current around the battery, the other is pushed out. (While only one magnet is attached to the battery the second one will be slightly repelled by the battery but with both magnets attached, the battery in the neighborhood of the magnets should be magnetically polarized in such a way that both magnets are attracted.) As a side effect, the magnetic field between the contrariwise polarized magnets will have a strong radial component which induces a voltage in the coil when moved parallel to the axis of the coil. This voltage compensates partly the voltage of the battery so that the current through the coil decreases when the speed of the assembly increases.
If you would just like to amaze your students by a simple setup which produces (rotary) movement you can avoid the tedious task of winding a long coil: Just take an AA-battery, one magnet, a short chipboard screw (made from steel) and a short piece of flex wire. Put the magnet on the head of the screw, connect the upward pointing tip of the screw to the negative pol at the bottom of the vertical battery. Due to magnetic attraction, the screw and the magnet will hang from the bottom of the battery. Connect the wire to the positive battery pole, and touch the side of the magnet with the other end of the wire. Magnet and screw will start to rotate fast. BTW, this is the principle of the homopolar (unipolar) motor first demonstrated by Faraday 1821.
Hope this helps.
Thank you very much for your help, Prof. Joerg Fricke . We did the experiment successfully, but the battery-magnet moved slowly and the motion distance was short. I see that the force causes the motion is proportional to the number of turns, the voltage of battery and the number of magnets. However, as the battery voltage increases, the size and mass of the battery increases. At the same time, as the number of magnets increases, the mass of the system increases, resulting in a large inertia that makes it difficult to move. I can not solve this problem.
The two magnets are conductors and they are coonected in the two opposite poles o the Li Battery. In addition; the two magnets are in direct contact with the cooper wire. So, these elements are equivalent to an electric circuit and gernerates an additional magnetic field that exerrts a Lorentz type force on the magnets which are integrally linked to the bloc system. Consequently, the system driven in motion.
The geometric shape and the spires regularity of the copper wire influence the nature of the movement: therefore for a rectilinear ring it is a decelerated movement; whereas for a perfectly circular wire, the movement would be circular uniform.
Spiral deformations cause friction that can seriously slow the movement.
Dear Dr. Nguyễn Thanh Lâm, given the usual (amazingly good) batteries and permanent magnets, the only means (besides of moistening all parts with low viscous oil which would cause a mess on your table) I can think of to make the effect stronger is:
In your video, the coil seems already to be covered by insulating material. If you have a pipe made of a ferromagnetic, electrically non-conductive material with virtually no hysteresis (I guess some kind of ferrite would be best), and with an inner diameter not much larger than the diameter of your electrically isolated coil, you could cover the coil by such a pipe. If no such pipe is available, you could nevertheless try by placing ferrite rods outside the coil.
While I'm curious myself whether this would improve the effect considerably, I feel that a demonstration with an open coil as in the youtube video might be more interesting looking even if the speed is low. (And with the ferrite cover, the setup would no longer deserve the adjective "simplest".)
Thank you very much for your help, Prof.Joerg Fricke and Prof.Mohamed El Hafidi!
- Badges
- Science topic
- Similar topics
- Physics