Understanding the Junction Rule for Circuit Analysis

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In summary, the junction rule for finding the current equation at node a in the given circuit is to list all currents flowing into the junction and out of the junction, and then set the sum of the incoming currents equal to the sum of the outgoing currents. In this case, the equation would be I(3)+I(2)=I(1).
  • #1
abcdmichelle
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Homework Statement


I need to find the current equation for the junction in node a in the following circuit:
http://i749.photobucket.com/albums/xx137/abcdmichelle/gjgjhg.jpg


Homework Equations



Current in = Current out so I(in)=I(out)

The Attempt at a Solution


The arrows in the diagram represent the direction of the current.
At node a I thought the junction rule would be

I(3)=I(2)+I(1)

Is this wrong?
I think it is but I don't understand why!?
Please help!
 
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  • #2
Yes, that is wrong... how did you come up with that?

Anyway, here's how you do the junction rule:
1. List all currents flowing in to the junction. This means, for each piece of wire connected to that junction for which the current arrow points into the junction, write down the associated current.
2. List all currents flowing out of the junction. This means, for each piece of wire connected to that junction for which the current arrow points away from junction, write down the associated current.
3. Write the junction equation, which is
(sum of list #1) = (sum of list #2)
 
  • #3
Thank you so much!

oh ok, so it would just be
I(3)+I(2)=I(1)

right?
 
  • #4
Yep, that's it.
 
  • #5
Thanks again! :) :) :)
 

What is the Simple Junction Rule?

The Simple Junction Rule, also known as Kirchhoff's Junction Rule, is a fundamental principle in electrical circuit analysis. It states that the sum of currents entering a junction in a circuit is equal to the sum of currents leaving the junction.

How is the Simple Junction Rule applied in practical circuits?

In practical circuits, the Simple Junction Rule is used to determine the direction and magnitude of currents at different points in the circuit. By applying this rule at each junction, we can solve for unknown currents and analyze the behavior of the circuit.

What are the limitations of the Simple Junction Rule?

The Simple Junction Rule assumes that the circuit is in a steady state, meaning that currents and voltage values do not change over time. It also assumes that there are no external sources of energy in the circuit. These limitations make it less applicable in circuits with changing currents or external power sources.

Can the Simple Junction Rule be used in circuits with multiple loops?

Yes, the Simple Junction Rule can be applied in circuits with multiple loops. However, in addition to using the rule at each junction, we also need to use Kirchhoff's Loop Rule to account for the voltage drops and gains around each loop in the circuit.

How does the Simple Junction Rule relate to the conservation of charge?

The Simple Junction Rule is based on the principle of conservation of charge, which states that charge cannot be created or destroyed in a closed electrical circuit. By applying this rule, we can ensure that the total amount of charge entering a junction is equal to the total amount leaving the junction, thus satisfying the law of conservation of charge.

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