Really really basic electricity - Formulas

[Hoosier Mann]

Howdy,

I just started working through Floyd's 'Principles of Electric
Circuits'. Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Of course, I really appreciate V for voltage in V (volts).

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules, and whenever you want to use one of the formulas, you
think in the units, so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

Right? Or is this "indirection" needed in the future?

 

[Tom Biasi]

"Hoosier Mann" <hoosiermann@returnto.sender> wrote in message
news:0j7qp5hve62g9qcfdu1him7pst097e8fl0@4ax.com...

Howdy,

I just started working through Floyd's 'Principles of Electric
Circuits'. Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Of course, I really appreciate V for voltage in V (volts).

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules, and whenever you want to use one of the formulas, you
think in the units, so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

Right? Or is this "indirection" needed in the future?

Perhaps you should concentrate on the concept of quantities vs. units of
measure.

 

[Jon Kirwan]

On Sun, 14 Mar 2010 11:04:33 -0700, Hoosier Mann
<hoosiermann@returnto.sender> wrote:

I just started working through Floyd's 'Principles of Electric
Circuits'. Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that

I am unfamiliar with Floyd's.

I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

But it sounds good, so far. Understanding the physical units
and some simple designators is fine.

You realize the following, but I'll write it anyway:

There can be some confusion, at times, between W for energy
("work" -- often, but not necessarily expressed in Joules)
and W for Watts (power, work per unit time, which also does
imply Joules per second and so is more specific than "work"
which does not necessarily imply any specific unit and may as
well be in ergs as in Joules.) Using either W or using J is
not universally applied. Often, the same author will use W
when talking physics and something else entirely when talking
electronics because of the possible confusion of W with
watts, which is a whole different thing.

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Then I need to mess you up a little. An ohm is a
Joule-second per Coulomb^2. Can you imagine a helpful
concept to put in mind for such units?

Of course, I really appreciate V for voltage in V (volts).

Well, don't get too complacent. But as I said earlier, you
already realize all this:

The term 'E' is far more frequently chosen when expressing
Ohm's law, E=I*R. (Which is picked as E for "electromotive
force." V would mean the specific unit of volts, while E is
general enough to possibly include weird units of
ergs/micro-Coulomb, even. Not that it would, but it is a
physical concept and not a specific unit, just as work is a
physical concept and not a specific unit; while ergs or
Joules are specific units, just as volts is a specific ratio
of specific units.

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules,

I guess I've settled more on J/Q, as C looks like capacitance
in Farads and I'd like to avoid that possible connotation.

and whenever you want to use one of the formulas, you
think in the units,

Yes.

so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

I'd use Q because it avoids the misunderstanding of C as
capacitance, which is expressed in Farads (usually.) And a
Farad is a Coulomb^2/Joule, not a Coulomb.

Right? Or is this "indirection" needed in the future?

I'm just a hobbyist in this area, so I'm going to be very
interested in what the professionals say they have picked out
for themselves.

For me? When writing electronics, I want specific units
implied, so I will use V for volts, R for Ohms (unit implied
by convention), C for Farads (unit implied by convention), I
for amps (unit implied by convention), Q for Coulombs (to
void C which, by convention, implies both capacitance and
Farads), J for Joules (to avoid W for work which might imply
Watts), and P for watts (power, with Watts specifically
implied by convention.)

If I write P=I^2*R, there is little immediate confusion
because almost everyone knows P is power and from I and R on
the other side they know the units are Watts. If I wrote
W=I^2*R, instead, I might get some momentary confusion while
someone takes stock of the right side and then realizes that
W is power, not work. And if I wrote W=1/2*V^2*C, someone
might complain that this equation isn't how one computes
power and that ideal capacitors don't exhibit power
dissipation, anyway. (When I really meant that the equation
was the energy stored on a cap, in Joules.)

Here's some fun. Provide a physics thought-model explanation
for each of:

Volts = Joules/Coulomb
Amps = Coulombs/second
Watts = Joules/second
Ohms = Joule-seconds/Coulomb^2
Farads = Coulomb^2/Joule
Henries = Joule-second^2/Coulomb^2

What does Joule-second "mean?" Why does Coulomb^2 appear so
frequently and what is it, really? How are all these ratios
"meaningful" from a physics standpoint and not an electronics
one? Or are they just ad-hoc, meaningless except that their
arbitrary combination is requried to make dimensional
analysis work out in the end?

Do you notice that Henries*Farads results in seconds^2? Does
this suggest that the square root will give you time? What
other ways can you combine the above units to get time?

Jon

 

[Dave]

Hey, just posted a copy of Ohm's Law and related formulas in pdf format to
alt.binaries.schematics.electronic, with your user name in the title. Check
it out. Might come in handy...

Dave

"Hoosier Mann" <hoosiermann@returnto.sender> wrote in message
news:0j7qp5hve62g9qcfdu1him7pst097e8fl0@4ax.com...

Howdy,

I just started working through Floyd's 'Principles of Electric
Circuits'. Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Of course, I really appreciate V for voltage in V (volts).

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules, and whenever you want to use one of the formulas, you
think in the units, so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

Right? Or is this "indirection" needed in the future?

 

[Hoosier Mann]

Tom,

At first I thought you had meant to write 'qualities' vs units,
because in my mind, a quantity is expressed in the units, so they are
the same.

Your post sent me to a search where I found the 'Dimensional analysis'
page on Wikipedia, which cleared things up a lot for me, and made me
realize why one should learn the quantities as well as the units.

Thanks!

On Sun, 14 Mar 2010 14:47:58 -0400, "Tom Biasi"
<tombiasi@optonline.net> wrote:

"Hoosier Mann" <hoosiermann@returnto.sender> wrote in message
news:0j7qp5hve62g9qcfdu1him7pst097e8fl0@4ax.com...
Howdy,

I just started working through Floyd's 'Principles of Electric
Circuits'. Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Of course, I really appreciate V for voltage in V (volts).

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules, and whenever you want to use one of the formulas, you
think in the units, so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

Right? Or is this "indirection" needed in the future?

Perhaps you should concentrate on the concept of quantities vs. units of
measure.

 

[Hoosier Mann]

Jon,

There sure is a lot to think about in that reply!

I did notice that you gave a meaning to 'E' as Electomotive force, and
I had seen that in Floyd's digital book before realizing I needed to
switch to the basic electronics book first. Before that, I had never
seen anyone explain why 'E' was chosen for the quantity, and it helps
me to remember it. Can you tell me why 'Q' is used for charge?

Thanks,
Hoosier Mann

On Sun, 14 Mar 2010 13:00:30 -0700, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Sun, 14 Mar 2010 11:04:33 -0700, Hoosier Mann
hoosiermann@returnto.sender> wrote:

I just started working through Floyd's 'Principles of Electric
Circuits'. Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that

I am unfamiliar with Floyd's.

I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

But it sounds good, so far. Understanding the physical units
and some simple designators is fine.

You realize the following, but I'll write it anyway:

There can be some confusion, at times, between W for energy
("work" -- often, but not necessarily expressed in Joules)
and W for Watts (power, work per unit time, which also does
imply Joules per second and so is more specific than "work"
which does not necessarily imply any specific unit and may as
well be in ergs as in Joules.) Using either W or using J is
not universally applied. Often, the same author will use W
when talking physics and something else entirely when talking
electronics because of the possible confusion of W with
watts, which is a whole different thing.

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Then I need to mess you up a little. An ohm is a
Joule-second per Coulomb^2. Can you imagine a helpful
concept to put in mind for such units?

Of course, I really appreciate V for voltage in V (volts).

Well, don't get too complacent. But as I said earlier, you
already realize all this:

The term 'E' is far more frequently chosen when expressing
Ohm's law, E=I*R. (Which is picked as E for "electromotive
force." V would mean the specific unit of volts, while E is
general enough to possibly include weird units of
ergs/micro-Coulomb, even. Not that it would, but it is a
physical concept and not a specific unit, just as work is a
physical concept and not a specific unit; while ergs or
Joules are specific units, just as volts is a specific ratio
of specific units.

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules,

I guess I've settled more on J/Q, as C looks like capacitance
in Farads and I'd like to avoid that possible connotation.

and whenever you want to use one of the formulas, you
think in the units,

Yes.

so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

I'd use Q because it avoids the misunderstanding of C as
capacitance, which is expressed in Farads (usually.) And a
Farad is a Coulomb^2/Joule, not a Coulomb.

Right? Or is this "indirection" needed in the future?

I'm just a hobbyist in this area, so I'm going to be very
interested in what the professionals say they have picked out
for themselves.

For me? When writing electronics, I want specific units
implied, so I will use V for volts, R for Ohms (unit implied
by convention), C for Farads (unit implied by convention), I
for amps (unit implied by convention), Q for Coulombs (to
void C which, by convention, implies both capacitance and
Farads), J for Joules (to avoid W for work which might imply
Watts), and P for watts (power, with Watts specifically
implied by convention.)

If I write P=I^2*R, there is little immediate confusion
because almost everyone knows P is power and from I and R on
the other side they know the units are Watts. If I wrote
W=I^2*R, instead, I might get some momentary confusion while
someone takes stock of the right side and then realizes that
W is power, not work. And if I wrote W=1/2*V^2*C, someone
might complain that this equation isn't how one computes
power and that ideal capacitors don't exhibit power
dissipation, anyway. (When I really meant that the equation
was the energy stored on a cap, in Joules.)

Here's some fun. Provide a physics thought-model explanation
for each of:

Volts = Joules/Coulomb
Amps = Coulombs/second
Watts = Joules/second
Ohms = Joule-seconds/Coulomb^2
Farads = Coulomb^2/Joule
Henries = Joule-second^2/Coulomb^2

What does Joule-second "mean?" Why does Coulomb^2 appear so
frequently and what is it, really? How are all these ratios
"meaningful" from a physics standpoint and not an electronics
one? Or are they just ad-hoc, meaningless except that their
arbitrary combination is requried to make dimensional
analysis work out in the end?

Do you notice that Henries*Farads results in seconds^2? Does
this suggest that the square root will give you time? What
other ways can you combine the above units to get time?

Jon

 

[Hoosier Mann]

Thanks! Got it and will print it to look at while driving to and from
work to learn this stuff. (I can do that and drive, but don't even
give me a phone while I'm driving!)

On Wed, 17 Mar 2010 08:30:03 -0500, "Dave" <db5151@hotmail.com> wrote:

Hey, just posted a copy of Ohm's Law and related formulas in pdf format to
alt.binaries.schematics.electronic, with your user name in the title. Check
it out. Might come in handy...

Dave

"Hoosier Mann" <hoosiermann@returnto.sender> wrote in message
news:0j7qp5hve62g9qcfdu1him7pst097e8fl0@4ax.com...
Howdy,

I just started working through Floyd's 'Principles of Electric
Circuits'. Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Of course, I really appreciate V for voltage in V (volts).

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules, and whenever you want to use one of the formulas, you
think in the units, so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

Right? Or is this "indirection" needed in the future?

 

[Jon Kirwan]

On Wed, 17 Mar 2010 17:19:56 -0700, Hoosier Mann
<hoosiermann@returnto.sender> wrote:

There sure is a lot to think about in that reply!

I did notice that you gave a meaning to 'E' as Electomotive force, and
I had seen that in Floyd's digital book before realizing I needed to
switch to the basic electronics book first. Before that, I had never
seen anyone explain why 'E' was chosen for the quantity, and it helps
me to remember it. Can you tell me why 'Q' is used for charge?

I don't really know. I have always imagined it as a name
meant as a reminder that the charge on electrons and protons
is countable, in _quantum_ units, and cannot be 1.6721, for
example. But I really have no idea.

Jon

 

[Jasen Betts]

On 2010-03-18, Hoosier Mann <hoosiermann@returnto.sender> wrote:

Jon,

There sure is a lot to think about in that reply!

I did notice that you gave a meaning to 'E' as Electomotive force, and
I had seen that in Floyd's digital book before realizing I needed to
switch to the basic electronics book first. Before that, I had never
seen anyone explain why 'E' was chosen for the quantity, and it helps
me to remember it. Can you tell me why 'Q' is used for charge?

Q for quantity, I think.

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

[John Fields]

On Wed, 17 Mar 2010 17:19:56 -0700, Hoosier Mann
<hoosiermann@returnto.sender> wrote:

Jon,

There sure is a lot to think about in that reply!

I did notice that you gave a meaning to 'E' as Electomotive force, and
I had seen that in Floyd's digital book before realizing I needed to
switch to the basic electronics book first. Before that, I had never
seen anyone explain why 'E' was chosen for the quantity, and it helps
me to remember it. Can you tell me why 'Q' is used for charge?

---
Please bottom post or inline post where appropriate.

"Q" is used for charge because the magnitude of the charge depends on
the _Quantity_ of electrons in the charge.

1 coulomb of charge, for example, contains 6.2e18 electrons.

JF

 

[Fred Abse]

On Wed, 17 Mar 2010 17:19:56 -0700, Hoosier Mann wrote:

Can you tell me why 'Q' is used for charge?

Quantity (of electricity).

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)

 

[Fred Abse]

On Wed, 17 Mar 2010 17:21:48 -0700, Hoosier Mann wrote:

Thanks! Got it and will print it to look at while driving to and from
work to learn this stuff. (I can do that and drive, but don't even
give me a phone while I'm driving!)

"Hey, you guys, watch this!"

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)

 

[George Herold]

On Mar 14, 4:00 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

On Sun, 14 Mar 2010 11:04:33 -0700, Hoosier Mann

hoosierm...@returnto.sender> wrote:
I just started working through Floyd's 'Principles of Electric
Circuits'.  Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that

I am unfamiliar with Floyd's.

I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

But it sounds good, so far.  Understanding the physical units
and some simple designators is fine.

You realize the following, but I'll write it anyway:

There can be some confusion, at times, between W for energy
("work" -- often, but not necessarily expressed in Joules)
and W for Watts (power, work per unit time, which also does
imply Joules per second and so is more specific than "work"
which does not necessarily imply any specific unit and may as
well be in ergs as in Joules.)  Using either W or using J is
not universally applied.  Often, the same author will use W
when talking physics and something else entirely when talking
electronics because of the possible confusion of W with
watts, which is a whole different thing.

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Then I need to mess you up a little.    An ohm is a
Joule-second per Coulomb^2.  Can you imagine a helpful
concept to put in mind for such units?

Of course, I really appreciate V for voltage in V (volts).

Well, don't get too complacent.  But as I said earlier, you
already realize all this:

The term 'E' is far more frequently chosen when expressing
Ohm's law, E=I*R.  (Which is picked as E for "electromotive
force."  V would mean the specific unit of volts, while E is
general enough to possibly include weird units of
ergs/micro-Coulomb, even.  Not that it would, but it is a
physical concept and not a specific unit, just as work is a
physical concept and not a specific unit; while ergs or
Joules are specific units, just as volts is a specific ratio
of specific units.

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules,

I guess I've settled more on J/Q, as C looks like capacitance
in Farads and I'd like to avoid that possible connotation.

and whenever you want to use one of the formulas, you
think in the units,

Yes.

so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

I'd use Q because it avoids the misunderstanding of C as
capacitance, which is expressed in Farads (usually.)  And a
Farad is a Coulomb^2/Joule, not a Coulomb.

Right? Or is this "indirection" needed in the future?

I'm just a hobbyist in this area, so I'm going to be very
interested in what the professionals say they have picked out
for themselves.

For me?  When writing electronics, I want specific units
implied, so I will use V for volts, R for Ohms (unit implied
by convention), C for Farads (unit implied by convention), I
for amps (unit implied by convention), Q for Coulombs (to
void C which, by convention, implies both capacitance and
Farads), J for Joules (to avoid W for work which might imply
Watts), and P for watts (power, with Watts specifically
implied by convention.)

If I write P=I^2*R, there is little immediate confusion
because almost everyone knows P is power and from I and R on
the other side they know the units are Watts.  If I wrote
W=I^2*R, instead, I might get some momentary confusion while
someone takes stock of the right side and then realizes that
W is power, not work.  And if I wrote W=1/2*V^2*C, someone
might complain that this equation isn't how one computes
power and that ideal capacitors don't exhibit power
dissipation, anyway.  (When I really meant that the equation
was the energy stored on a cap, in Joules.)

Here's some fun.  Provide a physics thought-model explanation
for each of:

 Volts = Joules/Coulomb
 Amps = Coulombs/second
 Watts = Joules/second
 Ohms = Joule-seconds/Coulomb^2
 Farads = Coulomb^2/Joule
 Henries = Joule-second^2/Coulomb^2

What does Joule-second "mean?"  Why does Coulomb^2 appear so
frequently and what is it, really?  How are all these ratios
"meaningful" from a physics standpoint and not an electronics
one?  Or are they just ad-hoc, meaningless except that their
arbitrary combination is requried to make dimensional
analysis work out in the end?

Do you notice that Henries*Farads results in seconds^2?  Does
this suggest that the square root will give you time?  What
other ways can you combine the above units to get time?

Jon

Yeah That's Great! (Except physicists use E for energy)

"> Ohms = Joule-seconds/Coulomb^2"

Here's my favorite for the above. In a quantum point contact there is
room for only one electron. (you can make these by bouncing two
really thin gold wires together) If you apply a voltage V, then the
uncertainty principle tells you that Delta(E) (the uncertainty in the
energy) times Delta(t) is h. (Planks constant)

Delta(E) is V*e, the uncertainty in the energy as the electron crosses
the contact.
Delta(t) is e/I, the time it takes.
so (V*e)*(e/I)=h or the resistance of the contact, R=(V/I) R=h/e^2.
(the quantum unit of resistance.) and h has units of angular
momentum... Joule-seconds.

George H.

 

[Jon Kirwan]

On Fri, 19 Mar 2010 00:21:18 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Mar 14, 4:00 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
On Sun, 14 Mar 2010 11:04:33 -0700, Hoosier Mann

hoosierm...@returnto.sender> wrote:
I just started working through Floyd's 'Principles of Electric
Circuits'.  Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that

I am unfamiliar with Floyd's.

I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

But it sounds good, so far.  Understanding the physical units
and some simple designators is fine.

You realize the following, but I'll write it anyway:

There can be some confusion, at times, between W for energy
("work" -- often, but not necessarily expressed in Joules)
and W for Watts (power, work per unit time, which also does
imply Joules per second and so is more specific than "work"
which does not necessarily imply any specific unit and may as
well be in ergs as in Joules.)  Using either W or using J is
not universally applied.  Often, the same author will use W
when talking physics and something else entirely when talking
electronics because of the possible confusion of W with
watts, which is a whole different thing.

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Then I need to mess you up a little.    An ohm is a
Joule-second per Coulomb^2.  Can you imagine a helpful
concept to put in mind for such units?

Of course, I really appreciate V for voltage in V (volts).

Well, don't get too complacent.  But as I said earlier, you
already realize all this:

The term 'E' is far more frequently chosen when expressing
Ohm's law, E=I*R.  (Which is picked as E for "electromotive
force."  V would mean the specific unit of volts, while E is
general enough to possibly include weird units of
ergs/micro-Coulomb, even.  Not that it would, but it is a
physical concept and not a specific unit, just as work is a
physical concept and not a specific unit; while ergs or
Joules are specific units, just as volts is a specific ratio
of specific units.

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules,

I guess I've settled more on J/Q, as C looks like capacitance
in Farads and I'd like to avoid that possible connotation.

and whenever you want to use one of the formulas, you
think in the units,

Yes.

so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

I'd use Q because it avoids the misunderstanding of C as
capacitance, which is expressed in Farads (usually.)  And a
Farad is a Coulomb^2/Joule, not a Coulomb.

Right? Or is this "indirection" needed in the future?

I'm just a hobbyist in this area, so I'm going to be very
interested in what the professionals say they have picked out
for themselves.

For me?  When writing electronics, I want specific units
implied, so I will use V for volts, R for Ohms (unit implied
by convention), C for Farads (unit implied by convention), I
for amps (unit implied by convention), Q for Coulombs (to
void C which, by convention, implies both capacitance and
Farads), J for Joules (to avoid W for work which might imply
Watts), and P for watts (power, with Watts specifically
implied by convention.)

If I write P=I^2*R, there is little immediate confusion
because almost everyone knows P is power and from I and R on
the other side they know the units are Watts.  If I wrote
W=I^2*R, instead, I might get some momentary confusion while
someone takes stock of the right side and then realizes that
W is power, not work.  And if I wrote W=1/2*V^2*C, someone
might complain that this equation isn't how one computes
power and that ideal capacitors don't exhibit power
dissipation, anyway.  (When I really meant that the equation
was the energy stored on a cap, in Joules.)

Here's some fun.  Provide a physics thought-model explanation
for each of:

 Volts = Joules/Coulomb
 Amps = Coulombs/second
 Watts = Joules/second
 Ohms = Joule-seconds/Coulomb^2
 Farads = Coulomb^2/Joule
 Henries = Joule-second^2/Coulomb^2

What does Joule-second "mean?"  Why does Coulomb^2 appear so
frequently and what is it, really?  How are all these ratios
"meaningful" from a physics standpoint and not an electronics
one?  Or are they just ad-hoc, meaningless except that their
arbitrary combination is requried to make dimensional
analysis work out in the end?

Do you notice that Henries*Farads results in seconds^2?  Does
this suggest that the square root will give you time?  What
other ways can you combine the above units to get time?

Jon

Yeah That's Great! (Except physicists use E for energy)

I see W for work a lot, variable-wise. However, terms like
KE and PE for kinetic (transitional or rotational) or
potential (gravitational, elastic, etc) energy are often seen
when expressing the meaning of some term like 1/2mv^2.

"> Ohms = Joule-seconds/Coulomb^2"

Here's my favorite for the above. In a quantum point contact there is
room for only one electron. (you can make these by bouncing two
really thin gold wires together) If you apply a voltage V, then the
uncertainty principle tells you that Delta(E) (the uncertainty in the
energy) times Delta(t) is h. (Planks constant)

Delta(E) is V*e, the uncertainty in the energy as the electron crosses
the contact.
Delta(t) is e/I, the time it takes.
so (V*e)*(e/I)=h or the resistance of the contact, R=(V/I) R=h/e^2.
(the quantum unit of resistance.) and h has units of angular
momentum... Joule-seconds.

Hi, George. And welcome back!

Yes, I exactly _wanted_ folks to "see" the idea of angular
momentum present there and then to move from that point to
something new.

It would have been very easy for someone to simply respond to
me that:

"Well, let's just re-order your resistance equation
into (Joule/Coulumb)/(Coulomb/second), which is
volts divided by amps. So, duh!"

All they would have done, instead, is to restate the obvious
whence the physical dimensions had arrived in the first place
and I had wanted a deeper observation than some shallow bit
of circular logic.

So thanks for that!

Jon

 

[George Herold]

On Mar 19, 12:58 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

On Fri, 19 Mar 2010 00:21:18 -0700 (PDT), George Herold





ggher...@gmail.com> wrote:
On Mar 14, 4:00 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
On Sun, 14 Mar 2010 11:04:33 -0700, Hoosier Mann

hoosierm...@returnto.sender> wrote:
I just started working through Floyd's 'Principles of Electric
Circuits'.  Well, actually I started with Floyd's 'Digital
Fundamentals', but decided I needed to know electricity in general to
understand the digital part.

As I am learning the basic formulas, it seems to be more complicated
to me that

I am unfamiliar with Floyd's.

I am learning Q for charge in C (coulombs), W for energy in
J (joules), and I for current in A (amps).

But it sounds good, so far.  Understanding the physical units
and some simple designators is fine.

You realize the following, but I'll write it anyway:

There can be some confusion, at times, between W for energy
("work" -- often, but not necessarily expressed in Joules)
and W for Watts (power, work per unit time, which also does
imply Joules per second and so is more specific than "work"
which does not necessarily imply any specific unit and may as
well be in ergs as in Joules.)  Using either W or using J is
not universally applied.  Often, the same author will use W
when talking physics and something else entirely when talking
electronics because of the possible confusion of W with
watts, which is a whole different thing.

R for resistance in omega (ohms) seems to be readily accepted by my
aging brain.

Then I need to mess you up a little.    An ohm is a
Joule-second per Coulomb^2.  Can you imagine a helpful
concept to put in mind for such units?

Of course, I really appreciate V for voltage in V (volts).

Well, don't get too complacent.  But as I said earlier, you
already realize all this:

The term 'E' is far more frequently chosen when expressing
Ohm's law, E=I*R.  (Which is picked as E for "electromotive
force."  V would mean the specific unit of volts, while E is
general enough to possibly include weird units of
ergs/micro-Coulomb, even.  Not that it would, but it is a
physical concept and not a specific unit, just as work is a
physical concept and not a specific unit; while ergs or
Joules are specific units, just as volts is a specific ratio
of specific units.

Now, you who did this eons ago probably just learned the formulas as,
say, V=J/C instead of V=W/Q, because the latter looks like watts and
not joules,

I guess I've settled more on J/Q, as C looks like capacitance
in Farads and I'd like to avoid that possible connotation.

and whenever you want to use one of the formulas, you
think in the units,

Yes.

so why learn that Q is charge in coulombs so the
number will always be followed by C (with a prefix, perhaps)?

I'd use Q because it avoids the misunderstanding of C as
capacitance, which is expressed in Farads (usually.)  And a
Farad is a Coulomb^2/Joule, not a Coulomb.

Right? Or is this "indirection" needed in the future?

I'm just a hobbyist in this area, so I'm going to be very
interested in what the professionals say they have picked out
for themselves.

For me?  When writing electronics, I want specific units
implied, so I will use V for volts, R for Ohms (unit implied
by convention), C for Farads (unit implied by convention), I
for amps (unit implied by convention), Q for Coulombs (to
void C which, by convention, implies both capacitance and
Farads), J for Joules (to avoid W for work which might imply
Watts), and P for watts (power, with Watts specifically
implied by convention.)

If I write P=I^2*R, there is little immediate confusion
because almost everyone knows P is power and from I and R on
the other side they know the units are Watts.  If I wrote
W=I^2*R, instead, I might get some momentary confusion while
someone takes stock of the right side and then realizes that
W is power, not work.  And if I wrote W=1/2*V^2*C, someone
might complain that this equation isn't how one computes
power and that ideal capacitors don't exhibit power
dissipation, anyway.  (When I really meant that the equation
was the energy stored on a cap, in Joules.)

Here's some fun.  Provide a physics thought-model explanation
for each of:

 Volts = Joules/Coulomb
 Amps = Coulombs/second
 Watts = Joules/second
 Ohms = Joule-seconds/Coulomb^2
 Farads = Coulomb^2/Joule
 Henries = Joule-second^2/Coulomb^2

What does Joule-second "mean?"  Why does Coulomb^2 appear so
frequently and what is it, really?  How are all these ratios
"meaningful" from a physics standpoint and not an electronics
one?  Or are they just ad-hoc, meaningless except that their
arbitrary combination is requried to make dimensional
analysis work out in the end?

Do you notice that Henries*Farads results in seconds^2?  Does
this suggest that the square root will give you time?  What
other ways can you combine the above units to get time?

Jon

Yeah That's Great!  (Except physicists use E for energy)

I see W for work a lot, variable-wise.  However, terms like
KE and PE for kinetic (transitional or rotational) or
potential (gravitational, elastic, etc) energy are often seen
when expressing the meaning of some term like 1/2mv^2.

">  Ohms = Joule-seconds/Coulomb^2"

Here's my favorite for the above.  In a quantum point contact there is
room for only one electron.  (you can make these by bouncing two
really thin gold wires together)  If you apply a voltage V, then the
uncertainty principle tells you that Delta(E) (the uncertainty in the
energy) times Delta(t) is h.  (Planks constant)

Delta(E) is V*e, the uncertainty in the energy as the electron crosses
the contact.
Delta(t) is e/I, the time it takes.
so  (V*e)*(e/I)=h or the resistance of the contact, R=(V/I) R=h/e^2.
(the quantum unit of resistance.)  and h has units of angular
momentum...   Joule-seconds.

Hi, George.  And welcome back!

Yes, I exactly _wanted_ folks to "see" the idea of angular
momentum present there and then to move from that point to
something new.

It would have been very easy for someone to simply respond to
me that:

    "Well, let's just re-order your resistance equation
     into (Joule/Coulumb)/(Coulomb/second), which is
     volts divided by amps.  So, duh!"

All they would have done, instead, is to restate the obvious
whence the physical dimensions had arrived in the first place
and I had wanted a deeper observation than some shallow bit
of circular logic.

So thanks for that!

Jon- Hide quoted text -

- Show quoted text -

Yeah, it's great to be home. (Spring arrived while I was gone.)

Angular momentum has to be one of the coolest (and most confusing)
quantities.

Joules-sec never makes much sense to me. I think of it as Joules/
Hz.... the faster you spin the more energy you've got.

George H.