How to Correctly Solve a Circuit Analysis Homework Problem?

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SUMMARY

The forum discussion focuses on solving a circuit analysis homework problem involving resistors and node connections. The user initially calculated the equivalent resistance (Req) as 10.56 ohms but was informed that the approach to redrawing the circuit was incorrect. A key mistake was identified in the handling of node connections, particularly with the 20k and 30k resistors, leading to a corrected equivalent resistance of 16 kilo-ohms. Properly following the current flow from the negative terminal was emphasized as crucial for accurate circuit analysis.

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  • Study the principles of node voltage analysis in circuit theory
  • Learn how to correctly redraw circuits for clarity and accuracy
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Students studying electrical engineering, particularly those tackling circuit analysis problems, as well as educators looking for examples of common pitfalls in circuit interpretation.

planauts
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Homework Statement


http://puu.sh/1faG5

Homework Equations


The Attempt at a Solution


http://puu.sh/1faFD

I labelled the nodes ^^.

I redrew the circuit based on the nodes, I ignored the 10 ohm resistor because it short circuits. (Note: I drew the series resistors in reverse order, 80 ohms should be between Node A and Node B, instead, I drew it between B&C. However, the result should be the same.)

http://puu.sh/1faFh
Based on this, the resistance is:
20 || 30 || (80+8)

Req = 10.56 ohms.

But that is not the answer, I'm not sure where I am going wrong, could someone please help me out please. Thanks a lot! Exam tomorrow :(
 
Last edited by a moderator:
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In your second drawing you have NODE C directly connected to terminal B. This is not how it is in the original drawing. I think you need to think a little more about how to redraw the circuit so that all the nodes and connections are preserved.

Eliminating the 10k resistor is fine; as you say, it's shorted out. The same short puts the top of the 20k resistor in contact with the bottom of the 30k resistor...
 
I got 16 kilo-Ohms, I think I understand what mistake I made now. I didn't follow the current from the negative terminal, I was just trying to make them connect. Makes sense now. :) THanks
 

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