Positive and negative - only words used to convey opposites?

[studiot]

Right or wrong, the choice of negative for the electron is quite independent of the choice of direction of conventional current, which is another different convention.

[Sorcerer]

Thanks guys, so for my second question. Since a simple switch between negative and positve don't commute, ie A * B = AB and -A * -B = AB (as well, not -AB)

Then what would be required to change the equations that have been developed around this, is it as simple as just inverting all the positive and negative signs or would the whole thing need to be re-written.

What implications would this have for other equations based off Maxwells, such as Einsteins special relativity. How far does the knock on effect go. Or does it not even begin?

 

I found John Cuthbers post interesting as when I asked my dad the same question he said the convention came about because of the elements used in the first batteries, one was higher on the periodic table so it was assumed that what was moving to it was negative (or something like that didn't really make sense to me).

Edited October 9, 2014 by Sorcerer

[Carrock]

Right or wrong, the choice of negative for the electron is quite independent of the choice of direction of conventional current, which is another different convention.

 

from http://www.mi.mun.ca/users/cchaulk/eltk1100/ivse/ivse.htm etc

Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source.

Where the charge carriers are electrons, this is only true if the electrons are defined as having negative charge ie the conventions aren't independent.

[studiot]

 

Where the charge carriers are electrons, this is only true if the electrons are defined as having negative charge ie the conventions aren't independent.

 

That's a fair question so perhaps you would like to tell me which way the conventional current flows through the capacitor in fig1, ie which direction is the direction of conventional current around loopABCD?

Is it flowing from positive to negative or negative to positive?

 

Now reverse the power supply to the resistor chain, as in fig2 and answer the same question.

 

 

 

[ajb]

Then what would be required to change the equations that have been developed around this, is it as simple as just inverting all the positive and negative signs or would the whole thing need to be re-written.

 

What implications would this have for other equations based off Maxwells, such as Einsteins special relativity. How far does the knock on effect go. Or does it not even begin?

There is the notion of charge conjugation, and importantly electromagnetism, gravity and the strong force are all symmetric under this operation. However the weak force is not.

 

Basically, if each charge q were to be replaced with a charge −q, which would have the effect of reversing the direction of the electric and magnetic fields the dynamics are of the same form for EM theory.

 

But this is slightly different to the opening post where the conventions for + and - are questioned.

Edited October 9, 2014 by ajb

[Carrock]

That's a fair question so perhaps you would like to tell me which way the conventional current flows through the capacitor in fig1, ie which direction is the direction of conventional current around loopABCD?

Is it flowing from positive to negative or negative to positive?

 

Now reverse the power supply to the resistor chain, as in fig2 and answer the same question.

'which way the conventional current flows through the capacitor'

As (ideal) capacitors don't pass direct direct current the answer is ( at different times ) left to right, right to left and there is no current at all.

 

'ie which direction is the direction of conventional current around loopABCD'

 

As current (and its direction and phase) varies around the loop (it may or may not change direction through CD) I can't answer this question or understand how it is the same as asking 'which way the conventional current flows through the capacitor'

 

 

'Now reverse the power supply to the resistor chain, as in fig2 and answer the same question.'

 

After transients have become negligible the answer is as above.

 

Was this a trick question?

[studiot]

It wasn't a trick question, but I said nothing about direct current.

 

I asked about conventional current and showed (part of) a circuit with two sources.

 

The AC source 'sees' a capacitor in series with two resistors in parallel with each other and circulates an (alternating) current through that circuit.

 

Which way does convention state that current to flow?

[Carrock]

It wasn't a trick question, but I said nothing about direct current.

 

I asked about conventional current and showed (part of) a circuit with two sources.

 

The AC source 'sees' a capacitor in series with two resistors in parallel with each other and circulates an (alternating) current through that circuit.

 

Which way does convention state that current to flow?

I can't give any better answer than in my previous post.

[Sensei]

Studiot, do you realize that AC on the 1st circuit won't be equal to 2nd circuit?

They will be shifted 180 degrees in phase (like sin(t) and -sin(t)).

[studiot]

 

Then what would be required to change the equations that have been developed around this, is it as simple as just inverting all the positive and negative signs or would the whole thing need to be re-written.

 

What implications would this have for other equations based off Maxwells, such as Einsteins special relativity. How far does the knock on effect go. Or does it not even begin?

 

The short answer is that some equations would change and some would not.

 

But you would not get rid of the inconsistencies by declaring electrons positive or by making conventional current flow from negative to positive.

[MigL]

Why has no one commented on the fact that Sorcerer, in post #27, gave the wrong definition for non-commutation ?

It should be...

A*B==B*A commuting

A*B=/=B*A non-commuting

[studiot]

Hello MigL

 

Actually I think the Sorcerer gave an appropriate view of his proposition by reversing all signs. He just was not using the correct term.

 

Communtation, which you have correctly stated, is a different process.

 

Also the Sorcerer was wrong in only considering multiplication.

 

Consider addition and subtraction of A and B versus -A and -B

 

7 - 5 = 2

 

but

 

(-7) - (-5) = -2

 

ie a sign change

 

So if are using signs to denote direction and polarity and then we swop all signs and subtract, we have a sign change.

[studiot]

In further consideration of my last post consider a battery connected to a circuit as in fig1.

 

Conventional current flows from the positive terminal of the battery (Q) to the negative terminal through the circuit.

Electrons flow from the negative terminal (P) to the positive through the circuit.

Circuit Voltage is reckoned as shown so that V = (Vq-Vp) and has the sign convention that increasing voltage get more positive.

 

Now reverse the signs on the charge so that electrons are now positive.

 

Note that we cannot physically reverse the battery so Q now becomes the battery negative and P the battery positive, and that electrons still exit the P terminal, regardless of its sign.

 

There are choices of adjusting the other conventions.

 

We can leave everything else the same as in Fig3

 

But hey,

 

Say we have a 10 volt battery and the circuit is a simple 10 ohm resistor so I is 1 amp, what happens.

 

Well Taking Vp as zero and using our definition V = (Vq-Vp) = ((-10) - (o)) = -10

 

What minus 10?

What happens now?

 

Well that means that we are putting in (-10) * (1) watts to our resistor = negative 10 watts.

so the sign convention is now at odds with most thermodynamic conventions that energy in is positive.

 

and what about good old ohms law?

 

Well we have to add a minus sign so that V = -(IR)

 

OK let's abandon this and revers our definition of votlage as in Fig2.

Note it is now again opposite to the direction of current.

 

We will now recover positive signs in our power and ohmic calculations.

 

But we have had to change two conventions to achieve this.