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### Topic: Does it matter if Resistor is connected to LED Anode or Cathode? (Read 13942 times)previous topic - next topic

#### TheVinivine

##### May 27, 2013, 06:13 pm
Hi!

I'm confused, some people saying that electricity flows from Negative to Positive, and some the other way.
I recently watch some beginner videos on YouTube about creating basic circuits with Arduino UNO, and regular circuits in general.
Some people on those videos were attaching Resistor to Cathode Leg of the LED and some to the Anode leg.

I don't know who is right, and I would be grateful is somebody could explain me:
- The difference?
- Does it matter if I attach Resistor to Positive (Anode) leg or to the Negative (Cathode) leg?

Thank you!

#### johnwasser

#1
##### May 27, 2013, 06:17 pm
Doesn't matter. The current flow (electrons per time) is the same in all parts of a series circuit. The LED and resistor can be swapped and the circuit still works the same.
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#### retrolefty

#2
##### May 27, 2013, 06:29 pm
A fundamental subject taught in formal electronics theory includes the various Kirchhoff's circuit laws. In your case with a simple series circuit it is taught that the current flow is identical at any point in the circuit, so swapping the order of the components has no effect on the current flow.

http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws

Lefty

#### fungus

#3
##### May 27, 2013, 07:01 pm
No.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### cjdelphi

#4
##### May 28, 2013, 04:26 pm
conventional current (+ to -)

in reality current flows from neg to pos.

#### retrolefty

#5
##### May 28, 2013, 07:03 pm

conventional current (+ to -)

in reality current flows from neg to pos.

Well electrons flow from neg to pos, but 'conventional current flow' definition is pos to neg. Really doesn't matter, use the definition that you are most comfortable with. The Air Force tech training used neg to post so that is what I use.

Lefty

#### pito

#6
##### May 28, 2013, 09:56 pm
Quote
The Air Force tech training used neg to post

That is because the lightning strikes from ground up to sky?

#7
##### May 28, 2013, 10:17 pm
http://www.srh.noaa.gov/jetstream/lightning/lightning.htm

All those electrons gotta go somewhere,

http://www.srh.noaa.gov/jetstream/lightning/positive.htm

or get backfilled from somewhere.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### ex-Gooserider

#8
##### May 29, 2013, 07:11 am
The direction of electric flow is yet another case of it being great to have so many different "standards" to choose from  ]

Some of it dates back to historical times before we knew as much about electrical stuff as we do today, some of it is the result of us humans applying random labels to natural phenomena that happen regardless of what we call them.

At any rate, for various reasons, Electrical Engineers tend to be taught that electricity flows from positive to negative, while Electronics Technicians are taught that it flows from negative to positive...  As stated earlier, both models work about equally well, take your pick as to which you use, however it can bite you to MIX the two...

About the only advantage to one over the other is that the symbols we use for schematics are based on the positive -> negative flow model, so all the directional component symbols for stuff like LED's, regular diodes, transistors, and such have the arrows pointing in that direction - current flows with the arrows, not against them...  If you use the negative -> positive model the flow is against the arrows which seems kind of counter-intuitive....

ex-Gooserider

#### kjkrum

#9
##### May 29, 2013, 09:16 am

The Air Force tech training used neg to post so that is what I use.

Navy/Marine avionics school taught the same.  The symbol for a diode certainly makes more sense if you think of "conventional" current instead of electron flow!  The mnemonic they taught us for current flow through a diode was that electrons can go up the ramp on one side, but they crash into the wall on the other side.  Now I get confused when I try to think about schematics in terms of conventional current.  Or think about conventional current at all, for that matter.

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