Resistors in series

timmeh87 · Post by **timmeh87** » Fri Jan 09, 2009 8:39 pm

Ok now lets do inductors, current sources, diodes, and crystal oscillators...

If you put ten 5A current sources in series across ten 100-ohm resistors in parallel, what voltage would you get across them?

If you put thirty 10V sources in parallel across 590 silicon diodes in series, can you figure out the current?

Bonus: If you put an ideal 5mA current source in parallel with a 10uF capacitor what voltage develops on the capacitor?

Post by **marshallh** » Fri Jan 09, 2009 11:09 pm

Mario wrote:Mmkay, here's the breakdown. When you put resistors in series, their values add. Put them in parallel, and the wattages add.
Put capacitors in series, and the voltages add. Put them in parallel, and the capacitance adds.

Nope, when you put resistors in parallel, the combined resistance is lower than the smallest resistor. Wattages are the same.
Capacitors in series are the same way - they essentially merge together to form one capacitors and the resulting capacitance is lower then the smallest capacitor.
The rest is right though

Kyo · Post by **Kyo** » Sat Jan 10, 2009 2:59 am

The calculation is
Resistors
parallel:
1/R = 1/R1 + 1/R2 + 1/R3 ...
therefore
R = 1/(1/R1 + 1/R2 + 1/R3...)
The new resistance is lower than the one of the lowest resistor. Think about it this way, they (as in the electrons) can go through that one, so they won't have more resistance, but some can also go through the oner ones at the same time, making the resistance even lower.
In series
R = R1 + R2 + R3...

for capacitors it's the same:
Capacitors
(I don't know which letter this is, so I just used an F)
parallel:
F = F1 + F2 + F3...
In series
1/F = 1/F1 + 1/F2 + 1/F3 ...
therefore
F = 1/(1/F1 + 1/F2 + 1/F3...)

Mario, I'm disappointed at you! You're so good with circuits usually

Rekarp · Post by **Rekarp** » Sat Jan 10, 2009 3:09 am

Anyone know what Inductors are? AND NO CHEATING (ie using the web and textbooks!)

Kyo · Post by **Kyo** » Sat Jan 10, 2009 3:11 am

Is translating cheating? Because otherwise I know

timmeh87 · Post by **timmeh87** » Sat Jan 10, 2009 2:23 pm

marshallh wrote:
Nope, when you put resistors in parallel, the combined resistance is lower than the smallest resistor. Wattages are the same.

Hes not entirely wrong... I mean the total wattage of your resistor network will increase.

Youd need about 4 resistors to get back to your original resistance though.
Or you could start with two of twice the intended value...

So if you need a 5W 10ohm resistor, you could use two 3W 20ohm resistors in parallel to make a 6W 10ohm resistor.
I know you know that marshall but yeah. Its for the rest of them.

Any answers to my questions yet

eurddrue · Post by **eurddrue** » Sun Jan 11, 2009 5:56 pm

Rekarp wrote:Anyone know what Inductors are? AND NO CHEATING (ie using the web and textbooks!)

actually I do, the are these little thingys that store energy in a magnetic field I believe

I know quite a bit about electronics. this 67-year-old dude lives about 8 hours away from me and is friends with my grandpa. He has been doing electronics since he was 12. I simply just called him

(the unfortunate part is he hates video games)

deviouskoopa · Post by **deviouskoopa** » Sun Jan 11, 2009 10:15 pm

Off the top of my head, I'd say inductors are the opposite of capacitors (so similar to resistors) because capacitors are 1/(jwC) in frequency domain but resistors and inductors are R and jwL respectively. Is that a good enough reasoning?

Haha I'm sure there's an easier distinction to make, like capacitors store voltage and inductors store current.

How about memristors?

deviouskoopa · Post by **deviouskoopa** » Sun Jan 11, 2009 10:17 pm

Well I had to look it up just to be sure, and memristors are similar to resistors, which makes the most sense I guess. Not that anyone cares/uses them.

timmeh87 · Post by **timmeh87** » Mon Jan 12, 2009 12:50 am

deviouskoopa wrote:Off the top of my head, I'd say inductors are the opposite of capacitors (so similar to resistors) because capacitors are 1/(jwC) in frequency domain but resistors and inductors are R and jwL respectively. Is that a good enough reasoning?

They are actually 'duals'. The duality of circuits is an interesting topic to study... It gives rise to some thing saying that if you replace every component with its dual and change all the parallel connections to series ones (and vice versa, and dont quote me on that), then it will still behave in the same way.

http://en.wikipedia.org/wiki/Duality_%2 ... ircuits%29

Also a good slipknot song

deviouskoopa · Post by **deviouskoopa** » Mon Jan 12, 2009 2:10 am

I wouldn't say they behave in exactly the same way... maybe in terms of impedance/admittance. You could be right though, but I have this gut feeling that I've learned something that says otherwise. I'm not knowledgeable enough to put my foot down basically

Rekarp · Post by **Rekarp** » Mon Jan 12, 2009 2:17 am

deviouskoopa wrote:Off the top of my head, I'd say inductors are the opposite of capacitors (so similar to resistors) because capacitors are 1/(jwC) in frequency domain but resistors and inductors are R and jwL respectively. Is that a good enough reasoning?

Thats how inductors act in Alternating Currents. In strict DC environments inductors are shorts

. Of course strict DC circuits only exist on paper and most circuits have slight fluctuations in there current.

timmeh87 wrote: replace every component with its dual and change all the parallel connections to series ones (and vice versa, and dont quote me on that), then it will still behave in the same way.

Correct Timmeh, thats what is called substitution.

timmeh87 · Post by **timmeh87** » Mon Jan 12, 2009 8:35 am

Sure that sounds right. I only remember the vague details of the infinity pile of crap Ive learned.

deviouskoopa: Im not trying to make this up, I learned it in school. Check the link

.