anode is it positive or negetive

[Clifton Arnold]

Help sombody fast is the anode positive or negitive I stuck
I can't remember.

[was_jlh]

positive

joe

[Clifton Arnold]

Thanks very much I just could'nt remember it. I must be getting very old. Whats that you say the first thing to go
is. Well I forgot it allready

[Ginseng]

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]

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

Joe

[Ginseng]

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

[was_jlh]

Not at all, Ginseng, you're right, I was in a hurry.

Joe

[PaulW]

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). [img]/ubbthreads/images/graemlins/blush.gif[/img]

Paul

[Ginseng]

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]

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

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

Daniel

[RussH]

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]

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]

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

[march.brown]

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 !

[VidPro]

yup there are just some words best left off the instruction sheets for connections :-)

[Ny0ng1]

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

[Mr Happy]

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 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.

[Databyter]

Heh, and I thought this thread was going to be about electro-plating!

[Petersen]

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]

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?

[SilverFox]

Hello Rjspeers,

Welcome to CPF.

When measuring a cell the anode is the + end. Your assumption is correct.

Tom

[Mr Happy]

Hello Rjspeers,

Welcome to CPF.

When measuring a cell the anode is the + end. Your assumption is correct.

Tom

Hi Tom,

I was going to answer this earlier, but then the forum stopped responding and I couldn't post.

However, I rather thought the anode of a battery is by convention the negative electrode and the cathode is the positive. All the references I find say this.

(And if in doubt it is best to avoid the anode and cathode labels altogether and just refer to the positive and negative electrodes. This will avoid any confusion with electrical engineers, chemical engineers, physicists, chemists, or anyone else... )

[samgab]

Yes, MH is right...

Confirmed by the source of all correct and indisputable info - Wikipedia: ( )

• In a discharging battery or galvanic cell (diagram at right) the anode is the negative terminal since that is where the current flows into the device (see drawing). This inward current is carried externally by electrons moving outwards, negative charge moving one way constituting positive current flowing the other way. It is continued internally by positive ions flowing into the electrolyte from the anode, i.e., away (surprisingly) from the more negative electrode and towards the more positive one (chemical energy is responsible for this "uphill" motion).
• In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receives current from an external generator. The current through a recharging battery is opposite to the direction of current during discharge; In other words, the electrode which was the cathode during battery discharge becomes the anode while the battery is recharging.

So as per the question, if you touch the probes of a DMM to an open circuit cell, the "+" terminal will be the cathode and the "-" will be the anode, right?

[sxl168]

Technically this is correct as a tiny amount of current is needed to be drawn from the cell in order for the DMM to read the voltage, however I would refer to SilverFox's post as the consensus opinion on labeling. The way I was always taught for this is that the electrode that generates anions (+ ions) is the anode and the electrode that generates cations (- ions) is the cathode in an electrochemical cell. The electrode designation obviously reverses depending on if you are charging or discharging a cell, but the polarity (+ and - terminal designations) of a cell does not change with charge or discharge, even though readings may go negative with cell over-discharge. The + and - terminal designations are reference points and are unvarying, the same fashion that a grounding point is designated as 0 Volts.

[Mr Happy]

The way I was always taught for this is that the electrode that generates anions (+ ions) is the anode and the electrode that generates cations (- ions) is the cathode in an electrochemical cell.

Let us apply this statement to a battery. When you connect a load like a voltmeter to a battery then electrons flow out of the negative electrode, through the voltmeter, and into the positive electrode. After the electrons flow into the positive electrode they combine with molecules in the electrolyte and cause negative ions to leave the electrode in solution. The positive electrode in a battery is therefore generating cations, and is consequently the cathode. It follows that in a battery the positive electrode is the cathode and the negative electrode is the anode.

[MagPap]

The way I was always taught for this is that the electrode that generates anions (+ ions) is the anode and the electrode that generates cations (- ions) is the cathode in an electrochemical cell. The electrode designation obviously reverses depending on if you are charging or discharging a cell, but the polarity (+ and - terminal designations) of a cell does not change with charge or discharge, even though readings may go negative with cell over-discharge. The + and - terminal designations are reference points and are unvarying, the same fashion that a grounding point is designated as 0 Volts.

Just a little correction for better undestanding. The positive +ions are the cations, and the negative -ions are the anions.

[sxl168]

After looking that up, I can't believe I had that backwards all these years. You are right about that and also you need to modify "the electrode that generates" to "the electrode that receives" in the post also.

[SilverFox]

In my defense, I read this question

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?

as trying to figure out which way to put batteries into a device and determining that by using a voltmeter. When you put the red + lead of the voltmeter on the + end of the battery and the black - lead of the voltmeter on the - end of the battery, you will read a positive voltage.

The question of which way the current flows is not important if you put the battery in backward and blow the device up...

Tom

[MagPap]

After looking that up, I can't believe I had that backwards all these years. You are right about that and also you need to modify "the electrode that generates" to "the electrode that receives" in the post also.

We can rewrite it: the electrode that receives anions (- ions) is the anode. Then, in an electrolytic cell, the anode is the positive terminal. ( the positive attract the anions' negative charge).

It has been explained better before:

or 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.

[45/70]

Once again, I find myself wondering how so much discussion can erupt over such a simple question LOL.

As far as a battery cell is concerned, the positive (+) and negative (-) poles are just that, and do not ever change, as has already been explained. As for anode and cathode, this is dependent on the direction of the flow of current. Is the battery, or cell being charged, or is it being discharged? Between these two conditions, the anode and cathode are reversed, again as has already been explained.

Dave