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> To true and why should they :)
A friend of mine worked in a mobile phone shop for a bit. During their
training the trainer asked some technical question about a phone which my
friend answered. Then she told everyone they were here to sell phones and
not to answer technical questions like that.
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scott wrote:
> What's a CRT monitor? Seriously, haven't seen one of them for years now.
In my universe, CRT is still infinitely more popular than LCD. This
might be related to price...
[Obviously, where I work most of the monitors are so ancient that the
plastic is turning interesting colours, so they're mostly CRT. My
monitor at home is also CRT, because this gives it the property that it
can display *any* resolution correctly. Useful for games that won't run
fast enough at high res...]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Stephen wrote:
> Volt amps takes into account the phase difference between the volts
> and the current. As you know then you pass an ac current through a
> capacitor or an inductor there is a phase difference. Volt amps is V *
> cos(phase) *A.
> Simple, What?
That makes no sense at all.
Since Amps are directly proportional to Volts, how can there possibly be
a phase difference?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> Since Amps are directly proportional to Volts, how can there possibly be
> a phase difference?
"Much to learn you have!"
Take a capacitor: initially it's discharged. Now connect it to a voltage
source, the first instant you do, the voltage across the capacitor is
still zero, however a large current (of charges) is flowing in,
accumulating on the cap's plates thus creating an electric field in the
cap. Which is proportional to the plate distance, charges sitting on them
and die dielectric. This field prevents further flow of charges into the
cap and finally you have the full voltage across the cap and no current
flowing. Now repeat the whole thing by applying the opposite of the
voltage, the cap gets charged the other way around, but with the same
principal timing. Repeat, repeat, repeat... you get the picture -> phase
shift (90 degrees).
Same applies to inductors (your speakers' driver coils), only this time
the energy is stored in the magnetic field produced by the current, so I
and V are exchanged in the timing, but still a phase shift.
That's very basic electrical engineering, you know... but maybe your
universe is different after all. SCNR
Michael
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> That makes no sense at all.
>
> Since Amps are directly proportional to Volts,
You know Ohm's law, V = I*R, well think what happens if V and I are complex
numbers ... as soon as R becomes complex, the phase of V and I will be
different.
And yes you guessed it, the "resistance" of capacitors and inductors are
complex numbers ;-)
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>> Since Amps are directly proportional to Volts,
>
> You know Ohm's law, V = I*R, well think what happens if V and I are
> complex numbers ... as soon as R becomes complex, the phase of V and I
> will be different.
>
> And yes you guessed it, the "resistance" of capacitors and inductors are
> complex numbers ;-)
That doesn't make any sense.
More precisely, if we assume that V and I are not necessarily in phase,
this immediately allows me to derive a contradiction.
Apparently, all I have to do is generate a sufficiently low-frequency
wave, with V and I sufficiently far out of phase, and we arrive at an
impossible situation. I could have a system with an arbitrarily large
current passing through it, for an arbitrarily long time, despite the
entire system having zero potential difference.
Obviously, electrons don't just move around for the hell of it. They
move in direct response to a potential difference. The very concept of a
current with no force driving it is obviously ridiculous.
The equations might make perfect sense in the presence of complex
numbers, but that doesn't mean they match the real world.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Michael Zier wrote:
> "Much to learn you have!"
True enough...
> Take a capacitor: initially it's discharged. Now connect it to a voltage
> source, the first instant you do, the voltage across the capacitor is
> still zero
How on earth do you work that one out?
If you connect a capacitor to a 9 V source, then the potential
difference across the capacitor is... exactly 9 V. In which universe is
that 0 V?
> That's very basic electrical engineering, you know... but maybe your
> universe is different after all. SCNR
Ah, maybe...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> That doesn't make any sense.
Oh yes it does, it's the basis for almost all electronic circuit design.
> More precisely, if we assume that V and I are not necessarily in phase,
> this immediately allows me to derive a contradiction.
>
> Apparently, all I have to do is generate a sufficiently low-frequency
> wave, with V and I sufficiently far out of phase, and we arrive at an
> impossible situation. I could have a system with an arbitrarily large
> current passing through it, for an arbitrarily long time, despite the
> entire system having zero potential difference.
Note that the complex version of Ohm's Law only holds for steady-state
continuous sinusoidal operation, it won't explain what happens when you
first turn on a circuit or suddenly introduce voltage or current
spikes/steps.
In your example, if you have previously charged up a capacitor an arbitrary
amount, then yes, you can then get an arbitrary amount of current out with
no voltage. Just charge up a capacitor with a constant voltage, then short
the terminals ;-) But the voltage must be in a sine wave cycle though for
Ohm's law to hold.
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On Wed, 2 Apr 2008 10:22:50 +0200, "scott" <sco### [at] laptop com> wrote:
>> To true and why should they :)
>
>A friend of mine worked in a mobile phone shop for a bit. During their
>training the trainer asked some technical question about a phone which my
>friend answered. Then she told everyone they were here to sell phones and
>not to answer technical questions like that.
>
One wonders why she asked if not to show the others how
unknowledgeable they were. I hate bosses like that.
--
Regards
Stephen
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On Wed, 02 Apr 2008 10:19:21 +0100, Invisible <voi### [at] devnull> wrote:
>Michael Zier wrote:
>
>> "Much to learn you have!"
>
>True enough...
>
>> Take a capacitor: initially it's discharged. Now connect it to a voltage
>> source, the first instant you do, the voltage across the capacitor is
>> still zero
>
>How on earth do you work that one out?
>
>If you connect a capacitor to a 9 V source, then the potential
>difference across the capacitor is... exactly 9 V. In which universe is
>that 0 V?
You don't do it directly you use a resistor in series to limit the
current. Michael left this step out for simplicity. Probably not
wanting to overload your brain :)
>> That's very basic electrical engineering, you know... but maybe your
>> universe is different after all. SCNR
>
>Ah, maybe...
--
Regards
Stephen
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