# Difference between RC and CR circuits

1. Jan 6, 2016

### esder

What would be the difference in measuring voltage across the resistor in this position and when resistor and capacitors positions are in different order? And why?
http://people.sinclair.edu/nickreeder/eet1150/PageArt/RCcircuitSimple.gif

2. Jan 6, 2016

### phinds

What do YOU think, and why?

3. Jan 6, 2016

### esder

I don't see the reason why it should be different unfortunately :/

4. Jan 6, 2016

### phinds

Why "unfortunately"

5. Jan 6, 2016

### esder

Because I would like to present you somehow that I was thinking hard before bothering you with this question but I didn't even know which way to go. Completely blank.

6. Jan 6, 2016

### phinds

Well, let me ask it differently. Why do you think there should BE any difference?

7. Jan 6, 2016

### esder

I came upon this somewhere on the dark side of the internet a long time ago, but it wasn't explained.

8. Jan 6, 2016

### phinds

I'll ask again, why do you think there should BE any difference?

9. Jan 6, 2016

### esder

Well, I have no idea why

10. Jan 6, 2016

### phinds

@esder, it is against the forum rules to spoon feed answers, and I would not do so even if it were not against the rules. Spoon feeding answers is boring for me and useless for you. I am trying to get you to THINK. What is your level of knowledge of electronics?

11. Jan 6, 2016

### esder

I am first year student and I am doing Mechanical, so it's very basic. I know what you meant, but as I said, I tried to come up with anything I failed.

12. Jan 6, 2016

### phinds

OK, but if you have such a tiny amount of knowledge of electrical circuits (and believe me, this problem is about as basic as they come), why spend you time worrying about a specific problem? You would be much better off spending a little time studying basic circuits. Once you have any kind of grasp of serial circuits you will see how trivial this particular problem is and more to the point you will have learned enough to solve similar problems.

13. Jan 6, 2016

### esder

Well, I think it's not that tiny. I know basic circuits, but I don't understand this at all.

14. Jan 6, 2016

### phinds

How does the current act in a series circuit?

15. Jan 6, 2016

### esder

It's the same through all the components.

16. Jan 6, 2016

### phinds

Bingo. So how could the voltage across the resistor be any different if you swap the R and the C? You see now how trivial this is?

17. Jan 6, 2016

For a basic understanding there are some valid analogies ( although PF-EE seems to hate them) - but have you seen anything like THIS and THIS ... do not get hung up on not understanding - it usually just means you need to take one (or two) steps back and look at the fundamental elements.

18. Jan 6, 2016

### jim hardy

Mechanical, you say ?

If you were asked to write equation of motion for a spring-mass-damper system
where would you start?

That was an exercise we had to do in freshman EE

Your question is analogous to force on a spring vs force due to friction

From the first link by windadct (he beat me to it !)
http://lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.html

force-voltage analog was more intuitive for me
though force-current works equally well

19. Jan 7, 2016

### meBigGuy

The voltage waveform across the resistor will be the same regardless of the order of the components. You are showing a dc supply, so there will be no current flowing in the steady state. If you add a switch, you can cause changes and the waveforms become more interesting. (and the answer will be the same)

But, on the other hand, there is a difference between a differentiator (C-R, output across the R) and an integrator (R-C, output across the C) which is not exactly what you asked, but might be what you were getting at.

Personally I dislike the approach taken when people try to get you to think by withholding information rather than just answering the simple question and moving forward.

20. Jan 7, 2016

### sophiecentaur

If the questioner is just trying to 'get something to work' then I would agree with you. Otoh, 'Education' usually involves getting students to think and work as much out for themselves as possible. A straight answer to a particular question can often not lead to any increase in understanding and, when a tutor is trying to assess a student's progress, it can give the wrong impression.
That's the reason for directing 'obvious' college type questions to the appropriate forum. If OPs always made it clear as to the context of their questions, there would be no problem, I think.

Last edited: Jan 7, 2016
21. Jan 7, 2016

### jim hardy

Ahhh i mis-read the question , thought he was asking about difference between voltage across two different components

i think OP already knows the answer maybe we just need to reassure him

It comes down to definition of voltage: potential difference
you've got to have at least two of anything to have a difference between them
a voltmeter has two leads for that reason

imagine yourself inside that voltmeter with its leads across the resistor
voltage across the resistor is I X R irrespective of the rest of the circuit
from inside the voltmeter you have no way of knowing where in the circuit that resistor is, or how many other elements are in the circuit

another way to think of it
it's a series circuit and voltages in series add
and addition we know from arithmetic is insensitive to sequence : A + B + C = A + C + B

any help?

Most of learning is discovering what we already know...

old jim