anode is it positive or negetive

Ginseng

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For goodness sakes man, that answer is incomplete.

Anode: The electrode where oxidation occurs in an electrochemical cell. It is the positive electrode in an electrolytic cell, while it is the negative electrode in a galvanic cell. The current on the anode is considered a positive current according to international convention; however, in electroanalytical chemistry the anodic current is often considered negative. Contrast with cathode.

For rechargeables: It operates as a galvanic cell during discharge and as an electrolytic cell during charge. As a consequence, the anode is the negative electrode during discharge, while it is the positive electrode during charge; at the same time, the cathode is the positive electrode during discharge, while it is the negative electrode during charge. This can create a confusing situation, and it is preferable to refer to the electrodes of a rechargeable battery as "positive" and "negative," because this designation is independent of the operational mode. Unfortunately, this nomenclature is not always followed. Often the "negative" electrode is designated as anode and the "positive" electrode is designated as cathode. This naming convention is a carry-over from the convention of the non-rechargeable battery.

For non-rechargeables: A battery in which the chemical reaction system providing the electrical current is not easily "chemically" reversible. It provides current until all the chemicals placed in it during manufacture are used up. It is discarded after a single discharge. Also called "primary" battery or cell. This battery always operates as a galvanic cell. Consequently, the anode is the negative electrode, while the cathode is the positive electrode.

Excerpted from Electrochemistry Dictionary

Wilkey
 

was_jlh

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Clifton, after reading Ginseng's post, I hope my answer did not mislead you, was going from my own experience.

Joe
 

Ginseng

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I hope I didn't come across as a bit intense. Just the thought of some guy hooking up a device to power and blowing it up because of polarity scares me.

Wilkey
 

PaulW

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Wilkey,

Wow! I've been studying electricity for over five decades, and I never knew that. So, if I'm getting it right, the positive terminal on a rechargeable being discharged is the cathode. But when being charged, current flows the other way and comes out of the anode, and now the anode is called positive -- even though the anode voltage is negative with respect to the cathode.

The part of all this that's new is calling the anode positive because the current exits here. In electrical engineering circles it is refered to as the negative terminal and retains that definition regardless of which way the current is flowing. The emphasis is on voltage, whereas in chemical engineering circles the emphasis appears to be on current. Upon thinking about it, I guess that makes sense. Chemists are concerned with the inner world of the battery and talk in terms of anode and electrode, while electricals are concerned with the world external to the battery and talk in terms of positive and negative.

Wilkey, when I first saw your post, I was in violent disagreement and started to get out my rarely used flame thrower. But I remembered that you usually know what you're talking about, so thought it would be good to make sure I did too by doing a bit of research. It was then that I discovered our differences were not in fact, but in perspective. One of the sources that I found contained this statement:

[ QUOTE ]
To help remember which electrode does what use the chemist's mneumonic term "REDCAT" ie. Reduction(RED) occurs at the cathode(CAT), and oxidation occurs at the anode. This is the chemical way of looking at it.

Physics people will tell you the cathode is positive(+ve) and the anode is negative (-ve) and electrons flow from the anode to the cathode through an external circuit.

Do you see the inherent conflict between these two statements.

[/ QUOTE ]

It's interesting how my background and consequent worldview so severely limits the way I can view things. Thanks for a different view (although I'm not at all comfortable with it). /ubbthreads/images/graemlins/blush.gif

Paul
 

Ginseng

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Exactly. And I am chemical engineer/chemist so you understand that my first instinct is for reduction-oxidation reactions (which flip flop in rechargeables) but as a flashaholic, I want the negative terminal to always be the anode, which it is not.

Wilkey
 

gadget_lover

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Now, on to power using devices as opposed to power producing devcies. /ubbthreads/images/graemlins/wink.gif

If I recall correctly, The anode of an LED is connected to the positive voltage source to allow current to flow.

Daniel
 

RussH

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Daniel, that works for me. But knowing that doesn't keep me from testing on my variable power supply, gradually bringing the voltage up. I fry enough LEDs without hooking 'em up backwards. Watch the Vr specs as well as Vf.
 

MrAl

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Hello,

This is an interesting question because the anode is
made positive for some devices and negative for other
devices.

A good example of this is the standard rectifier diode
vs the zener diode. To get the rectifier diode to
conduct the anode is made more positive then the cathode,
but for the zener diode it's the other way around...when
the zener conducts it's trying to maintain its breakdown
voltage.

An LED is basically the same as a diode: its anode is
made more positive then its cathode to get it to
conduct and light up.


Take care,
Al
 

MicN

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Hi - Mic here, newbie in Cairns Australia.

Aviation Engineering (EASA & CASA) is teaching 'electron flow' as opposed to 'conventional current flow'.

Electron flow from -ve to +ve around the circuit, and from +ve to -ve inside the battery.

Reverse of this for 'conventional current' flow.

Anode negative, Cathode positive during discharge

Hey have any of you guys got a formula for calculating the 'repelling force' (and units of expression for this) between like polaraties given in Coulombs?

I got as far as F = 'constant' x (Q1 x Q2 divided by the distance squared), however not clear on what the constant is all about. Also I think the unit is Newtons - is that correct?

Exam tomorrow, will check in later tonight - thanks in advance!! Mic
 
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march.brown

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I don't want to upset anyone , but - - - -

My batteries all have a little plus printed at the pointy end and a little minus printed at the blunt end ... I'm gonna stick with that ... All my torches need the batteries to go in with the pointy end (+) towards the LED and the blunt end (-) towards the other end where the spring lives.

Most people seem to stick with this method.

You don't really need to know your "A's and K's" in too much detail to take the dog out in the dark.

No offence was meant or implied by this post !
 

Ny0ng1

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6 years thread ressurection :lol:

very good info though I prefer the simplified version.

This thread also reminds me of people always asking on where to connect the car batteries during a jumper cable charging or starting a car with dead battery :D
 

Mr Happy

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Oh, interesting to come across this thread after it got bumped!

One thing just caught my eye though:

Wow! I've been studying electricity for over five decades, and I never knew that. So, if I'm getting it right, the positive terminal on a rechargeable being discharged is the cathode. But when being charged, current flows the other way and comes out of the anode, and now the anode is called positive -- even though the anode voltage is negative with respect to the cathode.
No, no, no, you have this backwards! :)

The positive end always remains the positive end, and the negative end always remains the negative end. It's the anode and cathode that switch ends during charging and discharging, not the positive and negative polarities.

While discharging the anode is at the negative end of the cell, while during charging the anode is at the positive end -- and the negative end then switches from anode to cathode.

The part of all this that's new is calling the anode positive because the current exits here. In electrical engineering circles it is refered to as the negative terminal and retains that definition regardless of which way the current is flowing.
Electrical engineering tends to define things according to the expected normal direction of current flow. For instance, consider a diode. When this is forward biased the current flows in the direction of the potential difference from positive to negative, and the electrons flow the other way, entering at the negative and and leaving at the positive end. The anode is where the electrons leave: the positive terminal! Just the same as a cell under charge.

The emphasis is on voltage, whereas in chemical engineering circles the emphasis appears to be on current. Upon thinking about it, I guess that makes sense. Chemists are concerned with the inner world of the battery and talk in terms of anode and electrode, while electricals are concerned with the world external to the battery and talk in terms of positive and negative.
There is no conflict between electrical engineering and chemical engineering, fortunately :D Unless polarity reversal has occurred, the positive electrode of the cell is always more positive than the negative electrode. Chemists and physicists do certainly agree about what is positive and what is negative, because regardless of which way the current is flowing the potential gradient between the electrodes does not change direction. When chemists are doing electrochemistry the actual voltage potentials at electrodes have everything to do with what reactions might be happening.
 
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Petersen

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k = 1/ (4 *pi *€)

(used the EURO sign as i "little Epsilon")

Where € is the permittivity of the medium in which the charges are situated.

This is taken from my old Engineering book " Electromagnetics"

PM me, if you want me to scan the page for you.

Good luck with the exam.


Hi - Mic here, newbie in Cairns Australia.

Aviation Engineering (EASA & CASA) is teaching 'electron flow' as opposed to 'conventional current flow'.

Electron flow from -ve to +ve around the circuit, and from +ve to -ve inside the battery.

Reverse of this for 'conventional current' flow.

Anode negative, Cathode positive during discharge

Hey have any of you guys got a formula for calculating the 'repelling force' (and units of expression for this) between like polaraties given in Coulombs?

I got as far as F = 'constant' x (Q1 x Q2 divided by the distance squared), however not clear on what the constant is all about. Also I think the unit is Newtons - is that correct?

Exam tomorrow, will check in later tonight - thanks in advance!! Mic
 

rjspeers

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Nov 26, 2011
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If you hook up a DC voltmeter with the red lead plugged into the meters positive socket and the black lead plugged into the negative socket then put the test leads across the terminals of a battery if the voltage reads positive am I to assume that the red lead is on the anode? I realize that current direction is the determining factor but would this not be reflected in the voltmeter reading?
 
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