Does Ohm's Law Apply to a Circuit with Current but No Voltage?

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Discussion Overview

The discussion revolves around the application of Ohm's Law in a circuit where current is present but the voltage between two points is claimed to be zero. Participants explore the implications of this scenario and the mathematical concepts related to indeterminate forms.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the applicability of Ohm's Law in a circuit where there is current but no measurable voltage between two resistors.
  • Another participant suggests that in an idealized scenario, connecting wires have zero resistance, leading to no voltage drop, but acknowledges that real wires have some resistance and thus a small voltage drop.
  • A participant notes that applying Ohm's Law to an ideal wire leads to an indeterminate form of 0=I*0, which raises questions about the nature of such expressions.
  • Several participants discuss the concept of 0/0 being indeterminate, with one explaining its context in limits and the need for further analysis to determine if a limit exists.
  • Another participant clarifies the distinction between indeterminate and undefined, providing examples of each and discussing their implications in mathematical contexts.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of Ohm's Law in this scenario, with some asserting it still applies under certain conditions while others highlight the confusion arising from ideal versus real components. The discussion on the mathematical concepts of indeterminate forms and undefined expressions also shows varying levels of understanding and interpretation.

Contextual Notes

The discussion includes assumptions about ideal versus real circuit components, the nature of voltage and current in specific configurations, and the mathematical treatment of indeterminate forms, which may not be fully resolved.

FS98
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in a circuit like the one in the attached picture, the voltage between two points in between two resistors should be 0.

But there is current flowing through the circuit.

So what’s going on here? Does ohms law not apply in this situation for some reason?
 

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Add the two points where you are taking measurements to the schematic.
 
Ohm's law still applies. In the idealized case, the connecting wires between the resistors have zero resistance thus essentially zero voltage drop is required to produce a current. In reality, there is some resistance and thus some small voltage drop between two adjacent points on the conducting wires.

(Assuming I understand your question.)
 
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One does not normally apply Ohms Law to an ideal wire because you get what I assume is confusing you which is V=IR leading to 0 = I*0 or I = 0/0 and the problem w/ that is that 0/0 is undefined.
 
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0/0 is indeterminate.
 
cabraham said:
0/0 is indeterminate.
In the context of a limit, 0/0 is an "indeterminate form". That is if one has two functions, f() and g() and if ##\lim_{x \to c}f(x) = 0## and ##\lim_{x \to c}g(x) = 0## then one cannot determine from that information alone whether ##\lim_{x \to c} \frac{f(x)}{g(x)}## exists or, if it does, what value it takes.

As a standalone formula, ##\frac{0}{0}## is simply undefined.
 
cabraham said:
0/0 is indeterminate.
What's the difference between indeterminate and undefined?
 
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phinds said:
What's the difference between indeterminate and undefined?
"Indeterminate" is used in the context of limits, as @jbriggs444 already said, and means that some work is required to determine whether they represent numbers. Some indeterminate forms are ##[\frac 0 0]##, ##[\frac \infty \infty]##, ##[\infty - \infty]##, and ##[1^\infty]##. Most textbooks write these forms in brackets to emphasize that they are "forms" rather than actual numbers.
The following limits are examples of the first three types I listed:
##\lim_{x \to 1}\frac{x^2 - 1}{x - 1}##
##\lim_{t \to \infty}\frac{t^2 + 2}{t^3 - 1}##
##\lim_{y \to \infty}y^2 - y^3##
These are called indeterminate forms because it's not obvious at first glance that they represent a number. By taking a limit and subsequent algebraic or other operations, one can determine that a limit actually exists or not.

As for undefined -- the division of any number by zero is undefined, as is taking the square root (or fourth root or any even root) of a negative number is undefined (if we're dealing with the real-valued square root function). In general, attempting to evaluate a function at a number not in its domain is undefined.
 
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