1
$\begingroup$

Long time reader, first time poster :)

I'm a first year physics teacher in a high school, and I'm running a science fair where students research their own topics and create demonstrations. One group has chosen electric motors, and they are making a motor out of a battery, paperclips, coil of wire, and a neodymium magnet. They have shaved off the top half of the wire's insulation. However, once we put the coil in the paperclips and try to spin it, though, it spins just a few times before being attracted to the magnet.

I've done this project before for my degree, but for the life of me I can't figure out what's going on here. The wire is definitely conducting electricity (quite hot to the touch), and I've double and triple checked that only the top half of the wire touching the paperclips is sanded. We have also tried magnets of varying strength, all to no avail.

Any advice?

Thanks ahead of time for your time and help!!

Example

$\endgroup$
  • $\begingroup$ I don't think your setup is correct. The direction of current through the ring is supposed to change every half-rotation so that the magnet keeps flipping it over and not attracting it. $\endgroup$ – Abhijeet Melkani Feb 8 '18 at 17:55
  • $\begingroup$ See this for example: elprocus.com/wp-content/uploads/2013/10/… $\endgroup$ – Abhijeet Melkani Feb 8 '18 at 17:56
  • $\begingroup$ @AbhijeetMelkani - With this set-up you will never achieve a change in direction of current. You can only get a rotation dependent break in the current flow. This suffices for it to work. $\endgroup$ – freecharly Feb 8 '18 at 18:18
  • $\begingroup$ Abhijeet, that link doesn't work for some reason. Might be my school wifi, though. $\endgroup$ – Henry Grumet Feb 8 '18 at 19:05
  • $\begingroup$ Unclear about precisely what's going on here. So a DC voltage is being fed to the motor? Also unclear about he meaning of "shaved off the top half of the wire's insulation". Does that mean that the insulation is not fully stripped off of the ends of the coil wire as shown in the diagram? $\endgroup$ – Samuel Weir Feb 8 '18 at 19:57
2
$\begingroup$

You have to check on the supporting ends of the wire how the shaved-off (blank) side of the wire is oriented with respect to the coil plane. If this is not done right, you will not get any sustained rotation.

It might perhaps be better do shave off the insulation completely and put on a new half insulation with a marker. As shown here where also possible reasons for a failure to work are given.

$\endgroup$
  • $\begingroup$ Very useful info! I'll send it to the student and see if that changes things. Thank you!! $\endgroup$ – Henry Grumet Feb 8 '18 at 19:04

protected by Community Feb 14 '18 at 12:25

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.