How Do You Calculate Total Resistance?

AI Thread Summary
Total resistance (RT) in a circuit can be calculated by analyzing the configuration of resistors, whether they are in series or parallel. A common mistake is misidentifying resistors as being in parallel when they are not, which can lead to incorrect calculations. The discussion highlights the importance of verifying calculations by checking voltages and currents in the circuit. A specific example mentioned involved a transformation from a delta (∇) to a wye (Y) configuration, which clarified the circuit's structure. Accurate identification of resistor arrangements is crucial for determining the correct total resistance.
Fatima Hasan
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Homework Statement



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Homework Equations


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R_b%3D%5Cfrac%7BR_a*R_b%7D%7BR_a+R_b%7D.gif


The Attempt at a Solution



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Could anyone check my answer please ?
 

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What is RT? What is the total resistance?

Usually an answer is easier to check than to get - calculate voltages and currents and see if they work out.
 
Why are you taking ##R_1## and ##R_2## to be in parallel? Here's what your circuit looks like after your ∇ to Y transformation:

upload_2018-10-26_9-55-37.png
 

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Just to be clear, your 6.22 Ohm answer is clearly wrong for the reason outlines by gneill.
 
gneill said:
Why are you taking ##R_1## and ##R_2## to be in parallel? Here's what your circuit looks like after your ∇ to Y transformation:

View attachment 232843
26%7D%5C%5C%5C%5C%3D6+%5Cfrac%7B15%7D%7B26%7D+%5Cfrac%7B609%7D%7B26%7D%3D30%20%5COmega.gif
 

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    26%7D%5C%5C%5C%5C%3D6+%5Cfrac%7B15%7D%7B26%7D+%5Cfrac%7B609%7D%7B26%7D%3D30%20%5COmega.gif
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Much better!
 
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