# Combining series and parallel resistors

Discussion in 'Homework Help' started by WayneDegu, Feb 7, 2014.

1. ### WayneDegu Thread Starter New Member

Feb 6, 2014
7
1
Dear Forum...

I am working on electronic circuits and really struggling to determine when resistors are in series or parallel in a mixed circuit.

Here is a question from an "All About Circuits" worksheet.

Which resistors do I combine together as parallel or series? I'm o.k. with all the calculations i.e. Ohms law, but it is just deciding how to pair off resistors that is causing problems.

It is question 40 on this sheet:

Wayne

John Ramelb likes this.

Apr 5, 2008
15,539
2,307
Hello,

Here is the original drawing:

Would it help if we "transform" as shown below:

Bertus

• ###### Question_40.png
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WayneDegu likes this.
3. ### WayneDegu Thread Starter New Member

Feb 6, 2014
7
1
Hello Bertus...

That's what I thought of doing. So, if R1 and R2 are in parallel, their combined resistance is 333.33 ohms. Then, combining in series with R3 and R4 we get:

333.33 + 150 + 450 = 933.33 ohms....which is not the 875 ohms quoted in the answer.

Am I missing something?

Thanks again,

Wayne

Apr 5, 2008
15,539
2,307
Hello,

Have a close look at the schematic.

R3 and R4 are in series.
This combination is parallel with R1.
This combination of R1, R3 and R4 is in series with R2.

Bertus

WayneDegu likes this.
5. ### WayneDegu Thread Starter New Member

Feb 6, 2014
7
1
Dear Bertus...

Many thanks...that seems to work out o.k.

How did you get the schematic from the original? Is it anything to do with the position of the battery?

Thanks again,

Wayne

Apr 5, 2008
15,539
2,307
Hello,

Nothing will change as long as the nodes stay the same.
I only moved the battery and a resistor outside the loop to make it more clear.

Bertus

• ###### Question_40_with remarks.png
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7. ### WayneDegu Thread Starter New Member

Feb 6, 2014
7
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Thanks Bertus, much clearer now.

Wayne