Re: American and British (English)

On Sun, 17 Aug 2008 01:41:02 +0100, "Peter Duncanson (BrE)"
<mail@xxxxxxxxxxxxxxxxxx> wrote:

On Sat, 16 Aug 2008 16:49:42 -0700, Hatunen <hatunen@xxxxxxx>
wrote:

On Sun, 17 Aug 2008 00:29:25 +0100, "Peter Duncanson (BrE)"
<mail@xxxxxxxxxxxxxxxxxx> wrote:

On Sat, 16 Aug 2008 15:55:17 -0700, Hatunen <hatunen@xxxxxxx>
wrote:

On Sat, 16 Aug 2008 23:37:47 +0100, "Peter Duncanson (BrE)"
<mail@xxxxxxxxxxxxxxxxxx> wrote:

On Sat, 16 Aug 2008 15:05:56 -0700, Hatunen <hatunen@xxxxxxx>
wrote:


Yes you can, but you cannot have current without voltage
difference.

Under normal circumstances. Take a conducting ring, poke a
varying magnetic field through the hole: current will flow
without a potential difference.

And if youc could find the voltage at two points on the ring, you
would find a voltage.

You can't find the voltage between any two points without
interfering with the current flow, thereby altering the
conditions by, for instance, diverting current out of the
magnetic field into a meter.

Any measurement interferes with the thing being measured. In the
case very small flows one uses a very high impdeance voltmeter to
minimise the interference.

Without such intervention the voltage between any two points is
zero.

So long as a current is flowing it cannot be; Ohm's Law is Ohm's
Law. There are complicating factors such as the inductance of the
ring. Remember you've postulated a varying magnetic field.

I postulated a varying magnetic field because only a varying
magnetic field will induce a current in a conductor.

Ohm's Law applies where current is created by the existence of a
voltage difference.

Nope.

It does not apply in the same way when the current is created by
induction -- the presence of a varying magnetic field.

Sure it does.

Perhaps someone else will follow this up. It's 1:36 am here and
I'm going to bed. I'll be back tomorrow.

P.S. Conventionally, electric current flows from positive to
negative.

Blame Benjamin Franklin for getting it wrong.

In the output coil of a generator or transformer it
flows in the opposite direction.

The true current, the electron current, flows out of the negative
terminal, through the load and into the positive terminal. The
so-called "conventional" current "flows" in the opposite
direction, "conventional current" having been adopted so that the
current would appear to flow from positive to negative in hopes
of leaving generations of engineering students unconfused..

Without a load there is no current from a generator or
transformer. Internally, the positive and negative terminals are
a result of the internal emf (voltage) induced by the magnetic
field. The designation of the terminals is due to the the voltage
appearing at the terminals, which exists with or without a
current, and the terminals have little meaning internally. There
is a voltage even without the load, and it is easily measured
(assuming the load of the measuring instrument to be negligible,
a fair assumption with modern electronic voltmeters).


--
************* DAVE HATUNEN (hatunen@xxxxxxx) *************
* Tucson Arizona, out where the cacti grow *
* My typos & mispellings are intentional copyright traps *
.

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