Solving Kirchoff's Law Questions: Finding Current Direction

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Discussion Overview

The discussion revolves around determining the direction of current in circuit problems related to Kirchhoff's laws. Participants explore methods for identifying current paths and the implications of their choices in the context of circuit analysis, particularly in preparation for exams.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant inquires about how to determine the direction of current in Kirchhoff's law questions when it is not provided in the circuit diagram.
  • Another participant suggests making an initial guess about the current direction and setting up equations accordingly, noting that if the guess is incorrect, the current will be negative, which can be adjusted later.
  • A follow-up question asks how to identify the starting and ending points of different currents (I1, I2, I3) in the circuit.
  • It is mentioned that currents typically start and end at junction points, and participants are encouraged to assume different currents between junctions or along different paths.
  • One participant shares a method used by their professor, which involves assuming all current flows away from each node, resulting in the sum of currents at a node equaling zero, although they personally find this method confusing.
  • A link to an external resource is provided to explain the professor's method further.

Areas of Agreement / Disagreement

Participants express differing views on the best approach to determining current direction, with some preferring to guess and adjust, while others follow a specific method taught by a professor. No consensus is reached on a singular approach.

Contextual Notes

Participants do not clarify the assumptions behind their methods, and there may be dependencies on specific definitions of current direction and junction points that are not fully explored.

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kirchoff's law??

Hi

Sometimes in kirchhoffs law questions it gives the circuit without showing the direction of the current so how do I determine the direction of the current (not the direction that I choose to solve the question)?

please help!
I have exam tomorrow
 
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If you don't know the direction of the current in a certain section of the circuit, simply make a guess, and set up your equations accordingly. If you guessed the wrong direction, the current in that section will come out negative, but the magnitude will still be OK, so remove the minus sign and flip the current-direction arrow around on your diagram.
 


thank you very much
I have another question if you don't mind
how do I know from where does I1 start and end? also for I2 and I3
 


Generally, the different currents start and end at junction points. You should always start out by assuming different currents between different junction points, or along different paths between the same two junction points.
 


My circuits professor always assumes that all current is going away from each node; so the sum of all the currents at a node equal 0. I personally haven't adopted this method because I find it confusing but and professor and some of my friends live by it. Here's a link that explains this method. The good thing about is you don't have to worry about signs until the end.

http://www.mathonweb.com/help/backgd5.htm
 


the different currents start and end at junction points.http://www.hergoods.info/avatar1.jpg
 
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