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Q & A: magnetic spring experiment

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Most recent answer: 03/07/2009
Q:
So I created a variable electromagnet by connecting a copper spring to a circuit. I chose to investigate if the extension of a spring has any correlation to its electromagnetic strength at the end of the solenoid. I kept the following constant. -Direction from earth's poles -Current/Voltage -type of spring -Circumference of the turns -And a couple of other things which I thought would make this investigation a fair test. So I got that the spring's extension is inversely proportional to the magnetic field as my hypothesis said, but I had an anomaly All my readings, except the first; were increasingly lesser than 20 mT lower than the previous reading. The difference between the first and the second reading was over 100 mT and I haven't been able to figure out why. I thought it had something to do with the fact that when the spring isn't extended, current can pass through the turns. But that hasn't led me to any conclusions. If you do have the answer, mail me at (deleted)
- Samay Kapadia (age 15)
Mumbai, Maharashtra, India.
A:
That sounds like a very nice experiment. Probably the slight shift over time was due to some rearrangement of the defects in the copper as it was stretched. If you take a similar spring and stretch it or compress it repeatedly mechanically, I bet you'll also find a little change in its unstretched extension. Getting a big change at first and smaller changes later is typical for this sort of effect.

Mike W.



(published on 03/07/2009)

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