Resistors and voltage

[john12ax7]

I see nothing wrong with wanting to understand the underlying physics,  it's actually required stuff for many EE degrees.

Yes,  you can design circuits without it.  But you will most likely design better circuits if you understand it.

 

[PRR]

There's a hole in the bucket.

BIG hole, bucket drains fast, large "current".

Little hole, bucket drains slow, small "current".

Instead of a hole we may use a hose. For the same diameter, a 1-foot hose will drain faster than a 1000-foot hose.

I'm not sure there is a fully satisfactory explanation in Classical Physics. Electrons bounce in conductors so not a direct path. "Friction"? Not exactly. Quantum Electrodynamics goes deeper, much deeper than I could follow.

For ALL my audio and similar problem, I figure conductors/resistors are just pipes with more or less stuffing in them. (The difference conductor or resistor is just whether it is sold to conduct or sold to resist. A length of "wire" can be a fine low-R resistor. A 100r resistor makes a fine jumper in a low-I circuit if you can stuff a resistor cheaper than cut and strip and stuff a wire.)

 

[JohnRoberts]

There's a hole in the bucket.

BIG hole, bucket drains fast, large "current".

Little hole, bucket drains slow, small "current".

Instead of a hole we may use a hose. For the same diameter, a 1-foot hose will drain faster than a 1000-foot hose.

I'm not sure there is a fully satisfactory explanation in Classical Physics. Electrons bounce in conductors so not a direct path. "Friction"? Not exactly. Quantum Electrodynamics goes deeper, much deeper than I could follow.

For ALL my audio and similar problem, I figure conductors/resistors are just pipes with more or less stuffing in them. (The difference conductor or resistor is just whether it is sold to conduct or sold to resist. A length of "wire" can be a fine low-R resistor. A 100r resistor makes a fine jumper in a low-I circuit if you can stuff a resistor cheaper than cut and strip and stuff a wire.)

gotta love the water analogy...

JR

 

[buildafriend]

A really basic thing that people don't all seem to pick up on is that voltage is the POTENTIAL DIFFERENCE BETWEEN TWO POINTS while current is the AMOUNT OF ELECTRONS MOVING THROUGH something. When you measure a voltage drop in a resistor you measure the difference from in to out, then ohms law works for DC. If you measure to ground you're accounting for a lot more things usually.

Voltage is a reference between two points, a potential difference
Current is the amount of electrons going through something

This is why you have to change probe inserts on a DMM.
Quiz question - which of each has a large resistance and a tiny resistance in an ammeter and in a volt meter? Why?

Resistance is what you explained..

Impedance is - in an under simplified way AC resistance which is non linear. Impedance has to deal with frequency and impedance changes at different frequencies. You would see this if you used an LCR meter to test at different frequencies

 

[Newmarket]

I see nothing wrong with wanting to understand the underlying physics,  it's actually required stuff for many EE degrees.

Yes,  you can design circuits without it.  But you will most likely design better circuits if you understand it.

+1 What he said 

It's good to have an understanding.
I assume that most people here have some degree of thirst for knowledge in general.
It'll also give some understanding of 1/f and 'Popcorn noise' and why a noise plot often goes up at very low frequencies.
Also why temperature and temperature stability can be important etc etc etc...

 

[JMFahey]

yes-I'm trying to understand the physical difference that happen with and without a resistor.

Define "without a resistor".
Are you talking an open circuit or a short circuit?
Both quite OPPOSITE situations can be described as "without a resistor".

There IS less current flowing with a resistor vs without a resistor. Right?

See above.

This is because the resistor is slowing down the speed that the electrons are able to get through the wire. Right?

WRONG.
And we already answered that.

To keep things simple, I am just thinking of a battery with a resistor between + and -

Ok, then current will flow from positive terminal to negative.
Actual electrons will frlow from negative terminaltopositive.
No speed slowing is involved, at all.  <-- remember this.

There IS less current flowing with a resistor vs without a resistor. Right?

If by "without a resistor" you mean a dead short, just a piece of wire, yes, through a short current will be infinite, so any other current will be less than infinite.

This is because

the resistor is slowing down the speed that the electrons are able to get through the wire.

Right?

No, No, No, read the answers, please.

You won´t make wrong Physics right just by insisting, it does not work that way.

From the negative terminal, the electrons can "see" that there are physical things (atoms and molecules?) that are in the resistor that is up ahead and so because of that resistance, only a certain number of electrons per second will be able to pass through that physical limitation and you can only have one electron leave the negative terminal for every electron that returns to the positive terminal, so that is the reason that there is less current when there is a resistor vs without.

Painting with a very wide brush: "yes" , "sort of" , "wouldn´t use those words", etc.

It can be and is explained way simpler, without delving into sub-atomic Physics and such:

* you have a battery which supplies "X" Volts.

* you connect a resistor across those terminals.
What is a resistor? : a device, a "thingie"  if you wish, which shows a measurable and very real property called "resistance".
Why/how/when/who/what? 
Well, you don´t *really*  need to know that to happily design Electronic circuits.
IF so inclined, fine with me, your local Library is chock full of Physics books to help you, not something which can (satisfactorily) explained and even less understood with a couple Forum questions.
Start reading and go as deep as you wish, you are welcome.

* when you connect that resistor as stated above, current will flow through it.
How much? :  I=V/R  ... just do the Math.

What if I vary V or R ?
Result will change.

You can even calculate current if R is infinite (open circuit) or zero (short circuit).
Go ahead, do it.

And of course use various V and R values.

Why are you wasting your time trying to tell someone what they shouldn't spend their time learning? 

HEY!!! WHO SAID THAT !!!!! 
You are being told to STUDY, and do it the RIGHT WAY.

How many times do I need to say that I'm interested in learning about this REGARDLESS of whether it applies to circuit design.

Then you are in the wrong Forum.
Try a Physics dedicated one instead.

Why do you care so much about trying to tell me what I SHOULDN'T learn?

Why are you asking then?

Please don't tell me what I should and shouldn't be concerned with learning, and then maybe the next guy won't waste his time trying to tell you what you should be spending your time doing.

Why are you asking then?

If my questions are irrelevant enough to this board, then I assume that John or another mod will tell me to stop.

That´s not the Moderator function.

Until that happens, if what I'm trying to learn about doesn't interest you or seems irrelevant, then why discourage someone else who is interested in it? 

You are encouraged to do it the right way.
If you insist on doing it wrong, it´s your problem and it will lead you nowhere.

In a nutshell: you have been *politely*  answered by knowledgeable Members, *all*  answers were relevant and to the point ... hope someday you can get something useful out of them.

And the Library visit invitation is still standing 

 

[john12ax7]

No speed slowing is involved, at all.  <-- remember this.

This is also incorrect. An electric field will impart a drift velocity. More resistance means less drift velocity, so in that direction there is indeed slowing. You might be thinking of propagation velocity which is more affected by permittivity.

It can be and is explained way simpler, without delving into sub-atomic Physics and such:
Then you are in the wrong Forum.
Try a Physics dedicated one instead.Why are you asking then?Why are you asking then?

He was asking because he specifically wants to learn what's going on at a deeper level. While it leans towards physics, solid state devices and quantum mechanics are generally required courses in electronics. So I see no issue with discussing it here.

In a nutshell: you have been *politely*  answered by knowledgeable Members, *all*  answers were relevant and to the point ... hope someday you can get something useful out of them.

I don't think telling someone they are WRONG is all that polite. It's a chill vibe around here, I wouldn't want to discourage people from wanting to learn.

 

[merlin]

OK, so it doesn't slow down, but is rather the actual physical number of electrons that pass through the point.  Speed doesn't change. 

Well, sometimes it does...
In metal wire you have billions of free electrons, in a very resistive material you don't have so many. The current in the metal lead wires is exactly the same as the current inside the resistor itself, of course, so in the metal leads you have many electrons moving very slowly (snail's pace), and in the resistive material you have fewer electrons moving more quickly (walking pace maybe). The electrons move faster in the resistor; they have to, in order to transfer the same amount of charge per second as in the metal. You can imagine it is the speed which is causing all the 'friction' inside the resistive material (energy dissipation), since the electrons don't have as much time to navigate the road and steer around the obstacles!

A more extreme example is a vacuum tube, where you have very few electrons but they reach thousands of kilometers per second before crashing into the metal anode, at which point it goes back to billions of electrons moving at snail's pace!

When you increase the resistance in your battery circuit, to reduce the current,  you are slowing down all the electrons in the circuit. They still move more quickly in the resistive material than in the metal wires, but everything has slowed (assuming all free electrons are taking part in the race, which is possibly not always true even at DC, so the physicists tell me).

 

[JohnRoberts]

If my questions are irrelevant enough to this board, then I assume that John or another mod will tell me to stop.

That´s not the Moderator function.

We can only point you toward the water, not make you drink it (and if PRR peed in the reservoir maybe don't drink that water).

There is nothing wrong with inspecting electronics at the atomic level, but IMO it is not the obvious, direct path to gain a usable  understanding of electronics in any reasonable time frame. 

People on the WWW are glad to answer any question (or try to), telling you what they think they know. This can be an interesting journey but not a direct path to functional ability.

==========

Decades ago I wanted to write this book, because I couldn't find it to buy. My ideal electronics book would start at the simplest entry level. The chapter on resistance would begin with the basic functional description. Reading deeper into the chapter would get progressively more detailed and harder to follow.  Beginners could read from the beginning, only as deep as they can handle at first pass then jump ahead to the next chapter on capacitors.. Experienced readers could skip the introductory early parts and dig into the meat of each chapter. If they bog down they only need to backup a few pages.  The book is intended to give people a good general knowledge from a light read, and as much as they can handle from a more rigorous read.

Of course I could never write this book, each chapter end would have to draw on experts from that given field to delve into the SOTA. The resistor chapter would be finished by some resistor industry expert. The introductory parts of each chapter should be written by one person for consistency and accessibility.  One problem I experienced trying to learn esoteric technology decades ago was that some texts/papers begin in the deep end of the pool.

JR 

 

[totoxraymond]

Hi,

I know this subject has been answered already but if someone's interested, electroboom made a very good video about resistance, speed of electricity, etc.

https://www.youtube.com/watch?v=IOb3-JZPY0Y

Thomas