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I Temperature fluctuations in helium

  1. Jan 24, 2017 #1
    I'm about to do an experiment on second sound in superfluid helium. Reading the lab manual it says we will generate it by putting a heater into the fluid and then passed an AC current through it. What we are going to measure is apparently the 'normal fluid fraction', which I guess under the two fluids model is the non-superfluid part. Weird thing: there's a casual mention that it should propagate away at twice the frequency of our current! Why would that happen?? I was trying to find some equations that would describe this behaviour but I can't, or at least those on the internet are way beyond me.

    Thanks for any help! :)
    Last edited: Jan 24, 2017
  2. jcsd
  3. Jan 24, 2017 #2


    Staff: Mentor

    See the PF Insights article, AC Power Analysis: Part 1, Basics

    From the article, V(t)*I(t) is the instantaneous power. When V and I are in-phase, V*I is double the fundamental frequency.


    Your experiment sounds like fun.
  4. Jan 24, 2017 #3
    I see, thank you! Yeah, it'll be a good experiment I think. In particular looking forward to using lots of liquid nitrogen, the safety briefing was just packed with interesting ways to go wrong!
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