How can voltage flow in a open circuit

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Discussion Overview

The discussion revolves around the concept of voltage in an open circuit, particularly addressing the apparent contradiction of having voltage present while current is zero. Participants explore the definitions and implications of voltage and current in various circuit conditions, including capacitors and ideal voltage sources.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses confusion about how voltage can exist in an open circuit, noting that according to Ohm's law (V = IR), if current (I) is zero, then voltage (V) should also be zero.
  • Another participant clarifies that voltage does not flow; rather, current flows when there is a potential difference and a conductive path. They mention that a charged capacitor can maintain a voltage without current flowing.
  • A different participant questions the notion of "voltage flow," suggesting that while a voltage can exist, it does not imply that it is flowing anywhere, especially in the case of a charged capacitor.
  • One participant introduces the idea of a traveling voltage wave along a wire, suggesting that voltage can change with time and position, even in an open circuit.
  • Another participant states that in an open circuit, voltage is not zero due to infinite resistance, leading to the conclusion that voltage can take on any finite value despite zero current.
  • A participant emphasizes the definitions of open and closed circuits, explaining that an open circuit lacks a complete path for current to flow, while a closed circuit allows for current flow.
  • One participant argues that in the case of an ideal voltage source, the voltage is dictated by the source, while Ohm's law applies to determine current, reinforcing the distinction between voltage and current in open circuits.

Areas of Agreement / Disagreement

Participants express differing views on the nature of voltage in open circuits, with no consensus reached on whether voltage can be said to "flow." The discussion remains unresolved regarding the implications of voltage presence without current.

Contextual Notes

Participants highlight the limitations of applying Ohm's law in certain scenarios, such as open circuits and ideal voltage sources, and the need for careful definitions when discussing voltage and current.

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Homework Statement


Hi Guys,

I am wondering how voltage can flow in an open circuit as I = 0 so surely V=IR; V = 0*R so V = 0

I know it does as when a capacitor is fully charged no current flows yet there is a voltage.

I'm about confused thanks!

Homework Equations


V = IR

The Attempt at a Solution

 
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Voltage doesn't flow. Current flows.

Current flows when there is a potential difference between two points and a conductive path between them. If the potentials at the two points are equal then no current flows.

A capacitor will accept charge (current will flow) so long as its potential difference is different than the potential difference across where it connects in the circuit if the capacitor happened to be removed (the "open terminal" potential difference).

If you think about it, a battery that's not connected to anything also maintains a potential difference between its terminals, yet no current flows.
 
I think you need to be clear about what you mean by "voltage flow".
In the case of a charged capacitor, would you really say that a voltage is flowing? Where is it going?
You would usually talk about a current flowing.

In the capacitor example, while it is charging, a current does flow - even though there is literally a break in the circuit. Can you see how this can be?

It is technically possible to have a signal represented as a voltage changing with time and position along a wire.
In this way it is possible to set up a traveling voltage wave in the wire - so, in this sense a voltage can be said to flow.
It is possible to send such a wave down a wire that is not connected to anything just like you can send pressure waves down a pipe.

When you start out learning about electric circuits, you are usually learning about the special case of DC steady-state circuits.
The current and voltage you are no doubt used to are defined with that situation in mind, and, in that situation, no electricity flows when there is an open circuit.
 
V = 0 Volts is a short circuit, and I = 0 Amps is an open circuit.

In an open circuit, the voltage is not zero because the resistance is infinite. All you know is that voltage = V = IR = 0*infinity. This is a meaningless value, and the equation essentially means the voltage can be any finite number. This is why you can have some voltage at an open circuit and have zero current due to the open circuit being represented by an infinite (or very large) resistance.

Hope this helped to clear things up!
 
V = 0 Volts is a short circuit, and I = 0 Amps is an open circuit.
... those are usually considered to be the DC consequences of an open or a short circuit - the labels are usually used to describe the physical condition of the circuit.

i.e.
An electric circuit is an "open circuit" if it lacks a complete path between the terminals of its power source.
An electric circuit is a "closed circuit" if it contains a complete path between the positive and negative terminals of its power source.
A short circuit is a type of malfunction of an electrical circuit.
... Wikipedia.
 
If you have an ideal voltage source connected to a resistor it's a mistake to think that the voltage drop across the resistor is determined by Ohms law. It's better to see it as the ideal voltage source dictating the voltage and then Ohms law dictates the current.

Same applies to an open circuit. The voltage is determined by the voltage source. The current is determined by Ohms law I = V/R = 0
 

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