# Resistance and current flow

I'm a programmer, but I have zero experience with electronics. I'm trying to figure why the following thing is true: why doesn't the location of the resistor matter? I know that "it's because they're connected in a row", but that's not the answer I'm looking for.

If we look at the following diagram:

http://www.robertstrains.net/simple%20LED%20circuit.jpg

A lot of things are unclear to me:

1. Why is the resister between the + terminal and the LED? doesn't the electricity flow from the - terminal to the + terminal?
2. If eletricity flows from the negative terminal to the positive, wouldn't the LED be 'first in the line' to get the larger current?even if it's for a milisecond, why doesn't this burn out the LED?

The reason this is so confusing to me, is because I use this anology:

I have a bucket of water, a box and a ball like this:

[Water(current)] [Box(resistor)] [Ball (led)]

If I pour the water out on the box, the box is gonna block out most of the water and the ball will only receive a little bit of water, but if I replace box with ball and pour the water directly to the ball, the ball is getting more liquid than the box, why doesn't the ball (LED) suffer? it seems like direction should make a difference and I'm trying to understand WHY it isn't?

Thank you!

kcoke: The reason this is so confusing to me, is because I use this anology:

So, don't.

Any analogy fails when strained or applied incorrectly.

To use the water analogy, you must picture it as a series of sealed pipes that always complete a circle back to a pump. The pump is the power supply. For water/current to flow out either end, water/current equal to it must flow into the other end.

So if I put a flow restrictor/resistor anywhere in a circuit, water flow/current is reduced in the entire series circuit. And water flow/current is the same anywhere in a series circuit.

The analog of voltage is water pressure.

So if I have a pump that is connected in a complete circle to a turbine, the turbine spins. But if I connect a valve in series/inline and adjust it to restrict water flow, it doesn't matter if I put it "before" or "after" the turbine, it has some pressure dropped across it that no longer appears across the turbine. So less water flow, the turbine spins more slowly.

If you add up the pressure drops across all of the turbines, valves, and pipes (pipes resist water flow a bit just as wires resist current just a bit), it must equal the pressure across the pump.

JimboZA: So, don't.

Why even post such a useless comment?

@Polymorph - thank you very much, Sir, It finally makes sense!!

kcoke: Why even post such a useless comment?

Oh the painful irony. On two levels.

kcoke: Why even post such a useless comment?

It wasn't useless at all: you said your confusion was in the fact that you were using a particular analogy. That means either the analogy was flawed or that you could not relate the analogy to the facts. In either case, stop using the analogy.

If eletricity flows from the negative terminal to the positive, wouldn't the LED be 'first in the line' to get the larger current

That is your fallacy, the same current flows instantly through all the components, it does not flow to one part and then on to another.

[quote author=Coding Badly date=1460566643 link=msg=2710183] Oh the painful irony. On two levels. [/quote]

1 If you refer to my original question as useless, this is question I didn't find the answer anywhere else, all the answers were "cuz they're not connected in parallel" which is not an answer for my question. If a complete beginner like me will have the same question, my "useless" comment would save them at least some time.

1. If you refer to my previous comment as useless, I was thanking the person who actually helped me, if that's useless, there's something wrong with you.

2. If you refer to my quoted "text" as useless, check point #2 + I only added additional comment, that was not my full message, maybe I want to know the answer? is asking someone why they bothered to respond, but not give an useful answer useless?

So what's the irony, Sir?

@jimboZA - i'm sorry if I seemed rude, I just wanted to know the answer to my question that has been bothering me and nobody really answered it, but by replaying then "don't", helps me absolutely in no way, just adds to the confusion and electronics can be very confusing for someone who started out 5 days ago.

Thank you Polymorph and Grumpy_Mike for clearing this up. such a simple detail added soooo much confusing for me, now it's finally clear! :)

kcoke: @jimboZA - i'm sorry if I seemed rude, I just wanted to know the answer to my question that has been bothering me and nobody really answered it, but by replaying then "don't", helps me absolutely in no way, just adds to the confusion and electronics can be very confusing for someone who started out 5 days ago.

Well I was also being a little tongue-in-cheek and perhaps should have used a precautionary smiley :) . I was also 110% sure that someone would be along in a few minutes to correct the analogy.

That said, I personally found over the years- and I'm no expert- that analogies are generally crap and are more trouble than they're worth.

You may find my photos from reply #7 onwards in this thread to be of use.

ahh man, if you added the smiley that would have changed everything!I wouldn't even get pissed and wouldn't respond haha crazy how much two bytes can change :D Thank you very much for the link!

kcoke:
1 If you refer to my original question as useless…

The material in question was referenced in my post as a quote. Which is why I quoted it.

So what’s the irony…

The first irony is that you spent time, energy, and money for the sole purpose of claiming a post was useless.

The second irony is that you wasted that time, energy, and money claiming a useful post was useless.

In other words…

kcoke:
Why even post such a useless comment?

Why would you post such a useless comment?

And, with this reply, the circle is complete. I have now posted this useless post explaining a useless post in which I mentioned the irony of a useless post.

The plumbing to electricity analogy is useful for teaching the novice the concepts of voltage = pressure, current = flowrate, resistance = valves, etc. But as soon as those concepts are solidly grasped, that analogy should be quickly and thoroughly forgotten.

outsider: Agreed.

kcoke:
A lot of things are unclear to me:

1. Why is the resister between the + terminal and the LED? doesn’t the electricity flow from the - terminal to the + terminal?

Firstly lets get a bit more precise here - electricity is a vague concept. It is electric charge that flows
and its net charge flow that matters (actually electrons in the wires are zipping around at vast speeds
all the time whether the wire is carry a current or not, but its the net macroscopic movement of charge
that we call a current.) Electrons carry a negative charge by convention, so they flow in the opposite
direction to charge. This is just a convention, but it is universally used.

You can talk about electron flow, or conventional current flow, but the physics is the same.

1. If eletricity flows from the negative terminal to the positive, wouldn’t the LED be ‘first in the line’ to get the larger current?even if it’s for a milisecond, why doesn’t this burn out the LED?

The net charge in any part of the circuit is very close to zero - everywhere the -ve on the electrons flowing in
the wires and components balance out the +ve charges on the atoms in the metal lattice. There is no
net charge anywhere (a very very good approximation for low voltage circuits). So if electrons flow in
one part of the wire they must flow at the same rate in every part of the wire. Otherwise net charge would
pile up and massive massive voltages would appear (millions of volts).

If there is an imbalance it will be cancelled out at the speed of light, so replace your millisecond by a
nanosecond and you are closer to the mark.

If it helps the relevant speeds are something like:

speed at which electric field reacts to balance out charge: 300,000,000 m/s
approx speed at which electrons random-walk in copper: 1,000,000 m/s
net speed for electron flow in copper at reasonable current densities: < 0.001 m/s
speed the current responds to changes in field is upto 300,000,000 m/s (stray inductance affects this)

The current in a conductor is responding to the field, the field is due to the distribution
of charges, the current acts to restore charge balance. Ohms law, V = IR reflects the
fact energy is expended moving electrons en-masse through a conductor.
[/quote]

You have to be very careful with the plumbing to electricity analogy - many years ago there was a humor piece in Readers Digest or something like that where they were using that analogy and then proceeded to expand on that into why doesn't the electricity come out of the outlets in the wall and run onto the floor? Don't you need to put those child plugs in the outlets to keep it from running out on the floor? By the time they got done I almost believed it :o

Every analogy breaks if strained too far. They are, after all, just analogies.