# Parallel/series circuit

Discussion in 'Homework Help' started by Niles, Jan 18, 2009.

1. ### Niles Thread Starter Active Member

Nov 23, 2008
56
0
Hi all.

Please take a look at the attached circuit.

Am I correct when I say that resistor 1 and 2 are in parallel, and these are in series with resistor 5, which are in series with the parallel resistors 3 and 4?

I hope you understand me. Thanks in advance.

Sincerely,
Niles.

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2. ### mik3 Senior Member

Feb 4, 2008
4,846
69
No you are not correct. Two resistors to be in parallel must have the same voltage across them. Do these resistors have the same voltage? No!

3. ### Niles Thread Starter Active Member

Nov 23, 2008
56
0
So when using Kirchhoffs law on each resistor, the same terms must appear on both sides for the resistors to be in parallel?

Thanks for responding quickly.

4. ### Niles Thread Starter Active Member

Nov 23, 2008
56
0
Is this a very good definition to use?

"A parallel circuit is one where the electrical components are connected between two points with one of the two ends of each component connected to each point."

5. ### mik3 Senior Member

Feb 4, 2008
4,846
69
I am sorry I didn't understand your question. Which Kirchhoff's rules?

6. ### mik3 Senior Member

Feb 4, 2008
4,846
69
Yes you can say it but have a look here too:

7. ### Niles Thread Starter Active Member

Nov 23, 2008
56
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Don't be sorry, I asked it in a very confusing way. Perhaps I should have asked: "How did you see that the voltage across resistor 1 and 2 are not the same?"

Thanks for the link. I'll check it out.

8. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
Here is an ebook link to the section on wheatstone bridge. This solution shows the application of mesh analysis rather than Kirchhoff's Voltage or Current Law. It may still prove helpful.

hgmjr

9. ### mik3 Senior Member

Feb 4, 2008
4,846
69
Because R5 has a voltage drop across it or because the bottom terminals of resistor 1 and 2 are not connected together with a wire but with a resistor.

10. ### Niles Thread Starter Active Member

Nov 23, 2008
56
0
Ahh, so you used Kirchhoffs loop rule on the loop containing resistor 1, 2 and 5. Very clever.

So when I am in doubt, I should use this strategy, and when the voltage across the two components are equal (i.e. there is no 3. contribution like in this case), I can conclude they are in parallel?

11. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
I believe that is a safe assumption.

hgmjr

12. ### Niles Thread Starter Active Member

Nov 23, 2008
56
0
I was more worried if my method of finding out when the voltage drop across the two components is equal is correct; can I just use Kirchhoffs loop rule for the loop containing the two components?

Thanks to both of you for participating.

13. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
When dealing with a loop, you must take into account all resistors that exist in the loop.

hgmjr

14. ### Niles Thread Starter Active Member

Nov 23, 2008
56
0
Thanks to both of you.