Why Is I Negative? A Closer Look at the Norton Method

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In summary, the reason why I is considered negative is because it is based on the passive sign convention, where the sum of currents entering a node is equal to the sum of currents leaving the node. This means that if you choose to sum the currents leaving the node, then any current entering the node will have a negative value.
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  • #2
I is negative because you consider it from - to + (as you show in your paper).
 
  • #3
i know that KCL says that the sum of the currents that goes in
equals the sum of the currents that goes out

here i don't know what current goes into the node
and what current goes out??
 
  • #4
transgalactic said:
here i don't know what current goes into the node
and what current goes out??

And you don't need to. The sum of currents entering a node is equal to zero, the sum of currents leaving the node is also zero. Pick one and stay consistent.

If you choose to sum the currents leaving the node, then by the passive sign convention you have (e-v)/R1 + e/R2 - I = 0. If you choose to sum the currents entering the node you have (v-e)/R1 + (0-e)/R2 + I = 0, which is exactly the same as the previous equation once you sort out the signs.

So, to answer your question, you are summing the currents leaving the node. Since I is entering the node it follows that -I is leaving it.
 

1. Why is I negative in the Norton method?

The I in the Norton method refers to the current flowing through a circuit. In this method, the direction of the current is assumed to be opposite of what is conventionally considered as positive. This is done to simplify the calculations and make the results more consistent with practical observations.

2. How does the Norton method work?

The Norton method is a technique used to simplify complex electrical circuits. It involves finding the equivalent current source and resistance of a circuit, which can then be used to solve for other parameters such as voltage and power. This method is based on the principle of superposition, where the total current in a circuit is equal to the sum of individual currents caused by each source.

3. What are the advantages of using the Norton method?

The Norton method simplifies complex circuits, making it easier to analyze and solve for important parameters. It also allows for the use of simpler mathematical equations, reducing the chances of errors in calculations. Additionally, this method is useful in understanding the behavior of circuits with multiple current sources.

4. Can the Norton method be used for all types of circuits?

The Norton method is applicable to both linear and nonlinear circuits, making it a versatile technique. However, it is most commonly used for circuits with multiple current sources, as it simplifies the calculations and provides a more accurate representation of the circuit's behavior.

5. Are there any limitations to the Norton method?

The Norton method assumes that the circuit is only composed of current sources and resistors, and does not account for other components such as capacitors and inductors. It also requires a good understanding of circuit theory and Ohm's law to be applied effectively. Furthermore, this method may not be suitable for circuits with high frequency AC signals or those with complex topologies.

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