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Homework Help: Gold Electrodes and Capacitance

  1. Apr 23, 2015 #1
    1. The problem statement, all variables and given/known data
    Well its 2 questions:
    1. Immersing a pair of gold electrodes in a saline solution in the presence of a fixed voltage causes the capacitance to:
      1. Increase

      2. Decrease

      3. Remain unaltered

      4. Increase briefly and then return to its original value
    2. Immersing a pair of gold electrodes in a saline solution in the presence of a fixed voltage causes the Current to: (same answers as above)

    2. Relevant equations

    3. The attempt at a solution
    I have been racking my brain over this for the last several hours. It was supposed to be made clear in a practical class that ended up having faulty equipment, but i digress...

    I basically began with the idea that the parallel plates would act as capacitors and when they were submerged in saline, it would act as the dielectric (higher relative dielectric than air). Given the fixed voltage, this would increase the charge that would be able to be stored by polarising the dielectric and reducing the electric field? (Am I at least on the right track here?) So i concluded that the capacitance would increase.

    The second question is the one that is giving me real trouble. I can't find any association between capacitance and current and I definitely don't understand how immersing gold electrodes in saline would change the current. The only thing I could come up with is the fact that the voltage is again fixed and given that voltage is proportional to current, would it be correct to say that the current shouldn't change? Or does the saline affect this?

    I was reading about how one electrode is - and the other is + and how the electrons are both being attracted by the protons and repelled by the potential voltage and so in a capacitor there is a point where there is no net charge movement because the forces are equal?? Again this was just something that kind of made sense.

    At this point I'm thinking that current would remain unaltered.

    Help would be much appreciated, Thanks
  2. jcsd
  3. Apr 24, 2015 #2


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    Homework Helper

    Inserting electrodes with a voltage into a saline solution changes it into an electrolysis setup.
    Since the voltage is kept fixed the question then becomes what happens to the charge at the electrodes.
    Last edited: Apr 24, 2015
  4. Apr 24, 2015 #3
    Ahh okay that makes much more sense now. Thanks for the help.
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