Electrical circuit general question

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Discussion Overview

The discussion revolves around a homework question related to electrical circuits, specifically focusing on current flow, resistance, and the implications of short circuits. Participants explore concepts such as Ohm's law and the behavior of electricity in series and parallel circuits.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant recalls that current is constant throughout a circuit and calculates it based on total resistance, suggesting a value of 6/5 Amperes.
  • Another participant corrects this by stating that current is the same through series elements, while voltage is the same across parallel elements.
  • A later reply introduces a consideration about lightning strikes and conductivity, but another participant advises against this line of reasoning and suggests using Ohm's law instead.
  • Some participants note that the question may be a trick question, while others argue it is straightforward based on the voltage across the series resistor.
  • One participant explains that a 3 ohm resistor in a short circuit would not have current flowing through it, leading to a current of zero.
  • Another participant questions the reasoning behind the path of least resistance and whether it applies in this scenario, prompting a clarification about how electricity behaves in parallel paths.
  • There is a discussion about the definition of a short circuit and the implications of zero voltage across a resistor in such a case.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of current flow in circuits, the implications of short circuits, and the validity of certain reasoning approaches. No consensus is reached on the best way to understand these concepts.

Contextual Notes

Some statements rely on specific assumptions about circuit behavior, such as the ideal conditions of zero resistance in wires and the implications of voltage across components. The discussion includes corrections and refinements of earlier claims without resolving the underlying disagreements.

chrisy2012
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Homework Statement


see thumbnail
second part

Homework Equations


V=IR


The Attempt at a Solution


I remember the professor saying that current throughout a circuit is constant no matter where it is. So adding all of the resistance together it should be 12/10 or 6/5 Ampere's. Is this correct?
 

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I cannot see a thumbnail :confused:
 
oops i swear i had it when i posted it. anyways it should be there now
 
Yeah, I'd say so...
 
chrisy2012 said:

Homework Statement


see thumbnail
second part

Homework Equations


V=IR

The Attempt at a Solution


I remember the professor saying that current throughout a circuit is constant no matter where it is. So adding all of the resistance together it should be 12/10 or 6/5 Ampere's. Is this correct?
No. He probably said the current through series elements is the same whereas the voltage across parallel elements is the same.
miniradman said:
Yeah, I'd say so...

No.
 
Last edited:
ahaha... how could I be so silly.

Sorry for the false infomation chrisy
but consider the reason why a lightning strike would rather move through nice conductive human liquids rather than a solid block of concretre. Then apply it to this circuit...
 
Don't do that consideration. Instead, use ohm's law. What is the voltage across the equivalent series resistance of 7 ohms? Simply take the voltage at one terminal and subtract it by the voltage at another terminal. Once you have this voltage,
I = v/R_eq
 
Note: this is a trick question.[/size]
N3OrO.gif



Just thought I'd better post that in case someone hadn't noticed it underneath the diagram. :wink:
 
NascentOxygen said:
Note: this is a trick question.[/size]
N3OrO.gif



Just thought I'd better post that in case someone hadn't noticed it underneath the diagram. :wink:

It's not a trick question. It's just a really easy question, considering what the voltage across that series resistor is.
 
  • #10
Oh I got it, the professor explained that the 3 ohm resistor is on the side of a short, so the current would not reach there. Therefore it's 0.
 
  • #11
chrisy2012 said:
Oh I got it, the professor explained that the 3 ohm resistor is on the side of a short, so the current would not reach there. Therefore it's 0.

Yeah, that's right. The equivalent series resistor of 7 ohms has the same voltage applied on both its ends.
I = 0/r = 0.
 
  • #12
Ohh what :smile:... why would my consideration be wrong then?

Can't you just say that electricity takes the path of least resistance which is in this case is the short circuit in the middle :-p

therefore there would be no current running through the 3 ohm resistor. Or is that scientifically incorrect (sorry for my ignorance, I'm only a laid back tween that goes to a public school)
 
  • #13
miniradman said:
Can't you just say that electricity takes the path of least resistance which is
Which is wrong. Electricity generally goes through all parallel paths, not just one of the many.

Only in the special case of a short circuit does no current go through other parallel paths. :smile:
 
  • #14
So if there was a parallel path with no added resistance, can it be called a short circuit?
 
  • #15
miniradman said:
So if there was a parallel path with no added resistance, can it be called a short circuit?

It's important to think about voltages since it tells the entire story. In ideal circuit theory, we say the little wires we draw have zero resistance. We also say everywhere on that wire has the same voltage since there is no resistance for there to be a drop in voltage as the voltage traverses the wire. So if you hook a resistor up at two points on this wire, known as a short circuit, you have some voltage V_a applied on both ends of it.

So the voltage across the resistor is the voltage at the first terminal minus the voltage at the second terminal:
V_a - V_a = 0.

If there is zero voltage, there must be zero current.
 

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