Can current flow in an open circuit?

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Discussion Overview

The discussion revolves around the behavior of current in an open circuit connected to a battery, specifically whether a current can flow momentarily and the implications of parasitic capacitance. Participants also explore the effects of a time-varying electric field on a wire with a resistor, questioning if this setup can produce measurable current.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that connecting a battery to an open circuit will result in a brief current flow due to the charging of parasitic capacitance, similar to how a capacitor charges.
  • Others argue that the setup described in the GIF represents a dipole receiving antenna, suggesting that it would measure alternating current (AC) voltage across a resistor.
  • A participant questions whether a multimeter connected in parallel to a resistor can accurately measure current, clarifying that it would measure voltage instead and infer current using Ohm's law.
  • One participant notes that the short piece of wire acts as one plate of a capacitor, with the rest of the universe serving as the other plate, leading to a very small capacitance value.
  • There is a mention of additional capacitance between the wire and the battery terminal, which could also influence current flow.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of current flow in the described scenarios, with multiple competing views regarding the behavior of current in open circuits and the effects of electric fields on wires.

Contextual Notes

Limitations include the assumptions about the behavior of parasitic capacitance and the definitions of current flow in open circuits. The discussion also relies on interpretations of the GIF without a clear consensus on its implications.

Salmone
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I have two related but separated questions:

1. If I have an open circuit connected to a battery, let's say an alkaline battery connected to a straight wire and nothing more, once I connect the battery to this wire there will be for a short time a current in the wire? Since in the battery due to redox a certain number of free electrons are "produced" and accumulated on the negative terminal, when I connect the battery to the wire, does the force excercised by these electrons push the free electrons on the wire toward the end of the wire until an equilibrium is reached and then the current will be zero? I have this doubt since I know that a capacitor in DC current will charge for a little amount of time with a certain current I flowing in the circuit, is this the same? I think that even a capacitor with only one plate connected to a battery will charge;

2. Is the system represented in this GIF physically realizable? Let's imagine that the "white tube" in the image is a wire with a resistor R and it is immersed in a variable electric field like the one in the image, will there be a current in the circuit with an accumulation of alternating positive and negative charges at the ends of the wire? Like if we put a multimeter on the resistance, will we always measure a passage of current?

https://upload.wikimedia.org/wikipe...eceiving_antenna_animation_2_800x403x15ms.gif
 
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-1- You are indeed charging the parasitic capacitance, so that circuit is a closed circuit just like it would be with an explicit capacitor that you were charging up.

-2- is just a receiving dipole antenna, no? So yes you measure the RX AC voltage across the resistor.
 
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berkeman said:
-1- You are indeed charging the parasitic capacitance, so that circuit is a closed circuit just like it would be with an explicit capacitor that you were charging up.

-2- is just a receiving dipole antenna, no? So yes you measure the RX AC voltage across the resistor.
Sorry, as always I don't understand answers at first sight:

1. I'm changing the question a bit: if we connect the battery to a wire with a resistor and a multimeter to the resistor, in the moment we connect the battery do we see current with the multimeter (current that will disappear after a certain time)? Like in the image below I've made with a highly refined graphic program(Paint).

2. I don't know what object is, I've used the GIF because I needed an example like that, a wire with a resistor in that kind of time-varying electric field will feel that movement of electrons, like in the GIF, and that current?

circuit.png
 
-1- You've labeled your meter with "A", but an ammeter would be in series with the resistor to measure the series current. As drawn in parallel, you would be using a voltmeter to measure the voltage drop across the resistor to infer the current via V = I*R. And yes, if you used a fast and sensitive enough measurement of the voltage across the resistor, you would see some current flow briefly as the parasitic capacitance from the piece of wire to the right of the resistor back to the battery + end was charged up.

-2- Well, what you have shown is just a dipole receiving antenna. In fact, you didn't say where you got the GIF (you should always provide a link for attribution), but it appears to be on the Wikipedia page for Dipole Antenna:

https://en.wikipedia.org/wiki/Dipole_antenna
 
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Salmone said:
If I have an open circuit connected to a battery, let's say an alkaline battery connected to a straight wire and nothing more, once I connect the battery to this wire there will be for a short time a current in the wire?
Yes.
Salmone said:
I have this doubt since I know that a capacitor in DC current will charge for a little amount of time with a certain current I flowing in the circuit, is this the same? I think that even a capacitor with only one plate connected to a battery will charge;
That short piece of wire is actually one plate of a capacitor, but of a very tiny value.

The other plate is everything else in the Universe, and the value of a capacitor is proportional to the size of its smallest plate and inversely to their separation (Area/Distance).

The "very tiny value" arises because the surface area of the wire is small and most of the Universe is so far away.

Hope this helps!

Cheers,
Tom

[edit:]
p.s. Strictly speaking, there is also some capacitance between the wire and the other battery terminal too.
 
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