Can current flow in an open circuit?

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SUMMARY

In an open circuit connected to an alkaline battery, a brief current flows when the battery is connected to a wire due to the accumulation of free electrons at the negative terminal. This phenomenon is similar to how a capacitor charges in a DC circuit, where the wire acts as one plate of a capacitor with a very small capacitance. Additionally, in a time-varying electric field, a wire with a resistor will experience alternating current, measurable across the resistor, as it interacts with the electric field. The system described in the GIF represents a dipole receiving antenna, which can indeed measure AC voltage across the resistor.

PREREQUISITES
  • Understanding of basic electrical circuits and components, including batteries and resistors.
  • Knowledge of capacitor behavior in DC circuits.
  • Familiarity with measuring instruments like multimeters and their configurations.
  • Concept of parasitic capacitance and its effects in electrical circuits.
NEXT STEPS
  • Study the principles of capacitor charging in DC circuits, focusing on time constants and transient responses.
  • Learn about dipole antennas and their operation in receiving alternating current signals.
  • Explore the concept of parasitic capacitance in electrical circuits and its implications on circuit behavior.
  • Investigate the use of oscilloscopes for measuring transient voltages and currents in circuits.
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Electrical engineers, physics students, hobbyists in electronics, and anyone interested in understanding transient behaviors in electrical circuits.

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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