A
Alan B
Would you care to explain why that is the simplest answer?
-
Categories
-
Platforms
-
Content
Would you care to explain why that is the simplest answer?
J
John Larkin
Sure, but it avoids addressing the "math problem", which actually
doesn't exist.
John
J
John Larkin
Because it makes the division meaningless hence harmless.
John
A
Alan B
It? What is *it*? Ohm's Law? Are you referring to division by zero
resistance in the equation I = V/R? If so, how does Ohms Law make this
division meaningless? Are you always so obtuse?
A
Alan B
Pretty soon you're likely to say something specific, but I'm not holding my
breath.
B
Bill Bowden
DJ said:
Isn't it still ohm's law?. For a parallel LC circuit, the reactance of
a super conducting 1 Henry inductor at 1 Hertz will be XL= WL or 6.28
ohms and therefore the peak voltage across the parallel LC circuit will
be 6.28 volts when the peak current is 1 amp, just not at the same
time?
Something like that?
-Bill
J
John Larkin
No, the lack of Ohm's Law.
As I think I mentioned, Ohm's Law isn't a physical law. So E/0 is no
different from 99/0; confusing perhaps, but not a physical
singularity.
"R" is just a definition of E/I in some particular quasi-steady-state
situation. As a definition, and not a physical reality, using it as a
denominator creates no real-world difficulties.
I'm always an electrical engineer, and I don't let definitions get in
my way. Real circuits never create mathematical singularities or
physical absurdities.
John
J
John Fields
C
Catch-22
Abstract said:
Is it a waste of time to exercise, expending energy when
it is put to no productive use. Oscillators oscillate.
Ideally we don't want to remove any energy out of them,
but they do have practical uses. They measure time,
which is not a waste of time. We shouldn't get upset
when an oscillator is being redundant. That's what it does.
Ancient greeks made knowledge of sqrt(2)=(1/sin(45)) a capital offense.
Some religions allegedly banned the number zero for a while. Others no doubt
banned infinity after the mathematician Cantor went insane. Let's face it,
numerology and religions have alot in common.
But an oscillator can fry itself out. It is possible to make a tank circuit
with too little resistance.
A
Alan B
No, you didn't mention that. You said that "Ohm's Law is not a law at
all," and failed to explain yourself.
I am not confused by the concept of division by zero. I am confused by
your style of writing, that seems to consist of stating claims and offering
no examples or evidence. For instance:
"The simplest answer is that Ohm's Law is not a law at all. It's never
true, and it's often wildly off."
I'd like some evidence that you know what Ohm's Law is, and some proof that
it is never true, and some examples of when it is wildly off. Simple.
That's a statement that must be taken in context. "R" is also a very real
phenomenon of electrical circuits, and your statement may be re-arranged to
include all the iterations of the E=I*R representative equation. What do
you mean by "quasi" steady-state? How do I plug "quasi" terms into a
steady-state equation?
It presents no real-world difficulties, as long as the practitioner
understands that the number being substituted for is a minute quantity.
Thus using the term "zero" simplifies equations and is not meant as a
precise representation of physical reality. (Bringing superconductivity
into the matter is, IMO, a separate issue, because doing so introduces a
basic shift in the underlying physics.)
I feel sorry for your cow orkers. It must be very difficult to work with
someone who is so loose with standards and practices for which definitions
exist. Are you familiar with ANSI and IEEE? Heaven forbid you ever get
acquainted with MIL-STD! Your career path would be littered with piles and
piles of discarded definitions. Come to think of it, I've know c
programmers who, similarly, don't let definitions get in their way. Their
products are predictably poor in quality and impossible to maintain.
So, is that akin to saying "there is no such thing as zero resistance in a
conductor," in an extensively more complicated way?
A
Alan B
I applaud the simplicity of your eloquence.
A
Abstract Dissonance
Alan B said:
How wonder how he can speak at all if he doesn't let any definitions get in
the way?
Radium said:
A zero ohm conductor will have zero volts drops on it, amperage flows
thru it is defined by other elements in the closed circuit.
Usually when you see a number devide by zero, one of these things might
happen:
1) A mislead thinking
2) A careless mistake
3) Typos
4) Some one gave you a wrong direction
5) Beyond of this scope
Cheers
J
John Fields
---
Strictly speaking, current doesn't flow through it, charge does.
Current, in amperes, is defined as the quantity of charge, in
coulombs, which moves past a fixed point in that conductor in one
second.
---
---
No, it isn't.
Consider, in the case you've brought up, if the conductor has zero
resistance, there will also be no voltage dropped across the
conductor, and we'll be left with:
E 0V
I = --- = ---- = ?
R 0R
---
---
Well, let's look at what's happening here.
1
If we say: --- = 1
1
-1
and ----- = 1
-1
it begins to look like if the divisor and the dividend are equal,
the quotient will always be 1 no matter what side of zero it's on,
so it would seem that at precisely zero:
0
--- also equals 1
0
After all, how many times can you fit nothing into nothing? Just
once, is my guess.
With that in mind then, the question becomes, IMO, "How much charge
_is_ there flowing around in there?
Let's look at the case of a superconducting ring in which one
coulomb's worth of electrons has been forced into motion around the
ring and that all of those charges pass by a fixed point on that
ring in one second. The current in the ring will be one ampere
because of the number of charges moving past the reference point in
one second.
But, note that that quantity of charge flows when both the voltage
across, and the resistance through, the ring are zero.
So, since:
E 0
--- = --- = 1
R 0
The induced charge flowing in the ring will be what it is times 1.
Which is to say that if 10 coulombs or ten microcoulombs were to be
induced into the ring, 10 coulombs or ten microcoulombs of charge
would be what flowed perpetually.
Unless you tried to measure it...
C
chuck
John said:
WOW!
G
Greg Hansen
Abstract said:
I'm surprised that dI/dt=V/L hasn't shown up yet in the discussion.
Even a straight wire has inductance. If there were a finite voltage
applied to a zero resistance, there still wouldn't be an infinite
current. There would be a current of I(t)=Vt/L.
P
PeteS
Greg said:
On the original matter, George Simon's law actually relates to metallic
conducting materials that have non-zero resistance. Many moons ago we
had to memorise a statement purported to be Ohm's law thus:
'The current through a metallic conductor is proportional to the
electromotive force across it's ends, provided the temperature and all
other conditions remain constant.'
This is close to what others report on a web search (it is some 35
years since I was required to remember that by rote
A zero ohm (truly zero) object falls outside the definition, though. In
that case, one gets closer to having to analyse the effect using
Lorentz force (from which Ohm's law can be derived). That includes
magnetic effects, as you mention.
Cheers
PeteS
G
G. Schindler
I tried to read all of the posts but it just became too wearisome so
forgive me if I repeat something already said.
First things first ..... dividing by zero is not in itself wrong! The
correct terminology, by the way, is 'undefined' not 'incorrect' and not
'error'. It is undefined because there are an infinite possibility of
answers. It is only an error because we had no way to tell the
calculator how to pick the correct answer. Simply put, your calculator
bombs out trying to do it because the people who programmed your
calculator had no way to know which answer to pick.
In actuality, division by zero can usually be solved as a limit.
Forgive me, but I am not going to put the time into developing the limit
equation. Though it should be simple enough it's been long enough that
I would have to do some real head scratching and would probably botch it.
Suppose you had a 2 volt source across a 1 ohm conductor. As you know,
the resulting current would be 2 Amps. Let's say, however, you measure
the voltage across one half the conductor. By measurement, you would
observe 1 volt across 1/2 ohm. This also calculates out to 2 amps since
it is in fact the same current as would be measured through the whole 1
ohm conductor. If this process were repeated until the conductor
section being measured was of zero length then the resistance of that
section of conductor would be zero, the voltage across it would be zero,
and yes it would still be carrying that same 2 amps as the whole conductor.
In this case: zero volts divided by zero ohms would be 2 amps.
Another way to think of this (without limits) is that if I had the
original circuit described above and we ADDED a zero ohm conductor in
series (be it an infinitely short conductor or a superconductor) we have
done nothing that would change the current through the conductor nor
change the voltage across the conductor.
The key to understanding this is that the zero ohms is not the entire
circuit resistance ... it is an infinitely small piece of a larger
circuit and by having zero ohms it has no effect on the ohms law
equation because the overall resistance is not changed.
forgive me if I repeat something already said.
First things first ..... dividing by zero is not in itself wrong! The
correct terminology, by the way, is 'undefined' not 'incorrect' and not
'error'. It is undefined because there are an infinite possibility of
answers. It is only an error because we had no way to tell the
calculator how to pick the correct answer. Simply put, your calculator
bombs out trying to do it because the people who programmed your
calculator had no way to know which answer to pick.
In actuality, division by zero can usually be solved as a limit.
Forgive me, but I am not going to put the time into developing the limit
equation. Though it should be simple enough it's been long enough that
I would have to do some real head scratching and would probably botch it.
Suppose you had a 2 volt source across a 1 ohm conductor. As you know,
the resulting current would be 2 Amps. Let's say, however, you measure
the voltage across one half the conductor. By measurement, you would
observe 1 volt across 1/2 ohm. This also calculates out to 2 amps since
it is in fact the same current as would be measured through the whole 1
ohm conductor. If this process were repeated until the conductor
section being measured was of zero length then the resistance of that
section of conductor would be zero, the voltage across it would be zero,
and yes it would still be carrying that same 2 amps as the whole conductor.
In this case: zero volts divided by zero ohms would be 2 amps.
Another way to think of this (without limits) is that if I had the
original circuit described above and we ADDED a zero ohm conductor in
series (be it an infinitely short conductor or a superconductor) we have
done nothing that would change the current through the conductor nor
change the voltage across the conductor.
The key to understanding this is that the zero ohms is not the entire
circuit resistance ... it is an infinitely small piece of a larger
circuit and by having zero ohms it has no effect on the ohms law
equation because the overall resistance is not changed.
J
Jim
Alan said:
Short circuit current would be limited by the power source internal
resistance..wouldn't it???
H
Homer J Simpson
No, it is wrong and the correct answer is error, not undefined.
Similar threads
- Simon Dice
- Electronic Basics
- Lee Carkenord
- Electronic Design
