11-04-2021, 05:28 AM
(This post was last modified: 11-04-2021, 05:53 AM by Erik Josefsson.)
(11-03-2021, 04:46 PM)solid Wrote: Two more things..
1) If you will replace the permanent magnet by a ferrite which is remagnetized at high frequencies you will not need the diodes. The ferrite is attracted by a coil with both current polarity.
2) The spring is itself a coil which should shrink when current of any polarity pass through it. I tried it just now, but the current is too low. A powerful signal generator can be used. The frequency can be determined by the smartphone from acceleration signal... An advantage of this technique is that the driving force should not depend on the oscillation amplitude.
....
Wow! You mean by 1) that I can replace the neodyme magnet with a ferrite rod antenna and use, for example, a 10.000 Hz + 10.002 Hz beat from an amplified phyphoxphone signal? But how would you know at what frequencies of the envelope's constituent sines would start to contribute to building of the "beat magnetic field" that is supposed to attract the hanging rod?
Btw, small ferrite rods are cheap, large are expensive:
https://se.rs-online.com/web/c/passive-c...rite-rods/
http://www.amateur-radio-antenna.com/fer...a-hfa3.php
Regarding 2) on the disadvantage of the force being 1/r2-dependent(?), you'd still get a forced oscillation, no? Resonance-peaks in the amplitude-frequency-graph (phyphox "Spring experiment") would perhaps be narrower compared to a graph when the resonance comes from a rotating device, but still show?
I think I have one of those ferrite rods hiding in grandpas old radio that I have saved for "maybe I'll fix it some day"-reasons.
Oh no, I have no time for this...
//Erik
PS. A resonance experiment (or any experiment) that students make on their own or in small groups has to be fast to assemble and take down, require almost no maintenance, and be made from either "standard physics course" components" or cheap components. The ferrite rod idea sounds promising in all respects!