Capacitor connected to battery at one end

  • #1
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Main Question or Discussion Point

I was recently solving a problem that involved a circuit with a capacitor that was connected to a battery at one end(the second plate just had a wire which didnt lead anywhere).

In the solutions it said that this capacitor cannot have any charge since there is no path for the current to flow, which makes sense. But on the other hand one end is connected to the battery which has some unknown(maybe very high) potential. Wouldnt some charge have to flow onto the capacitor to ensure that it is equipotential?
 

Answers and Replies

  • #2
davenn
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Wouldnt some charge have to flow onto the capacitor to ensure that it is equipotential?

no, for the same reason you have already stated.

Potential, or more correctly, potential difference is measured between two places

So, if you put the negative of your voltmeter on the battery negative and the positive probe any where from the
positive of the battery terminal, along the wire to the capacitor plate, you will measure the battery voltage

No current needs to flow to achieve that situation

Dave
 
  • #3
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But on the other hand one end is connected to the battery which has some unknown(maybe very high) potential. Wouldnt some charge have to flow onto the capacitor to ensure that it is equipotential?
What you are actually thinking of here would be a different circuit. This would be a small stray capacitance with ground. The value of this capacitance would be largely independent of the capacitor, and more related to how close it is to the ground. So it would be a different circuit where there is a path for current to flow.

Based on the question it seems that they wanted you to ignore that small stray capacitance.
 
  • #4
sophiecentaur
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Based on the question it seems that they wanted you to ignore that small stray capacitance.
This situation is in the twighlight zone between basic circuit theory and real circuits and it causes difficulties for many students. Problems that deal with this region of Physics should always be stated in full and the question that was set hasn't been specified tightly enough.

Hopefully the PF response will have put the OP at ease.
 

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