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Re: Jumping Ring Demo



I have a problem with all the explanations given for the phenomenon except that given by Doug Craigen:

The apparatus that I have in lab is asymmetrical. The the coil is not inside the ring but below it. There is a soft iron core which couples the coil and the jumping ring. The ring jumps when an AC source is connected to the coil.

Suppose the coil were oriented with a horizontal axis, and the ring were placed around the center of the coil. When AC current is applied to the coil, which way would the ring jump, left or right?

It would appear to me that due to (perfect?) symmetry it wouldn't jump either way. This implies to me that the phenomenon has something to do with the gradient of the field created by the coil.

In Martha Trakat's original question she mentioned trying to analyze the effect of the gradient. The requirement of a gradient was mentioned by Doug Craigen in his response.

I would appreciate if someone would tell me where my thoughts are wrong or if someone would expand on Doug's explanation. I don't know if the references given by Karl Trappe deal with this; I don't have easy access to old issues of AJP.

Rick Morra
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Rick Morra
Technology Coordinator / Physics Teacher
Pascack Hills High School
Pascack Valley Regional High School District
225 W Grand Ave
Montvale NJ 07645

Tel: 201-358-7052
Fax: 201-358-7019
E-mail: rmorra@pascack.k12.nj.us
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