# Parallel/Series questions

Discussion in 'General Electronics Chat' started by MusicTech, Apr 8, 2008.

1. ### MusicTech Thread Starter Active Member

Apr 4, 2008
144
0
NEW QUESTION:

this page has the mesh law, I don't quite get why there is 2(I1+I2). I understand both I's, but given their explanation do not quite see why the 2 is there as the coefficient.

old question: I didn't want to start a new thread, I always feel like I am posting just for the sake of posting when I do that.

On this link, I have a question on one of last figures it has the parallel resisors and it shows the battery with both voltage source and Rinternal, (the one that they call the parallel-series combo. The say that all the voltage will be supplied right back to Rinternal leaving none leftover for R1, 2 and 3. I read over the explanation a couple times, and don't really get why there is none left over for 1,2 and 3, but there is all for internal. Logically I am thinking, shouldn't the voltage at very least have to pass over at least one of those resistors to get to Rinternal.

So I don't get why this is, if someone could explain this phenonema to me differently, or more simply, that would be greatly appreciated, thanks

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
The short applied across one of the parallel resistors ends up effectively short circuiting all of the resistor at the same time. The parallel combination of the three resistors and the short circuit is pretty much zero. That means that there is not voltage drop across the parallel resistors. This forces all of the voltage from the battery to be dropped across the internal resistance.

hgmjr

3. ### MusicTech Thread Starter Active Member

Apr 4, 2008
144
0
ohhhh, I see, so basically, electricity wwants to go from the negative end of the battery to positive as quickly as possible, and since the resistors on parallel are shorted and can't carry electricity, the only way the electrons can get to the negative end is through the resistor in the battery.

4. ### hgmjr Moderator

Jan 28, 2005
9,030
214
That is basically what is happening.

hgmjr

5. ### MusicTech Thread Starter Active Member

Apr 4, 2008
144
0
ok I get it now, thanks

6. ### David Bridgen Senior Member

Feb 10, 2005
278
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With a short across any of the three resistors, the circuit simplifies to:

7. ### MusicTech Thread Starter Active Member

Apr 4, 2008
144
0
sure, ok I see.

If I may pose a new question:

this page has the mesh law, I don't quite get why there is 2(I1+I2). I ge both eyes, but given their explanation do not quite see why the 2 is there as the coefficient.

8. ### sixstringartist Member

Apr 8, 2008
18
0
when you are doing loop analysis you sum the voltages around a loop. To do this you take the resistance (impedance) times the current going through the component. For R2 on that link, the current flowing through it is due to I1 and I2 and the coefficient comes from the resistance of R2. Multiplying these together gives you a voltage which is a piece of the total voltage loop.