Re: Effect of the supply internal resistance


"Greg Neill" <gneillRE@xxxxxxxxxxxxxxxx> wrote in message news:498ed579$0$22975$9a6e19ea@xxxxxxxxxxxxxxxxxxxxxxx
Rich wrote:

+---------+--E2 = 0.1V
| |
[10R] R2 |
| |
+---E1
| |
[90R] R1 |
| [1R]
+--Ebat |
|+ |
[BAT] |
| |
| |
| |
+---------+


BAT is suppossed to be a device with zero resistance. So, you can
erroniously conclude there is 10V across 1R, thinking one part of 1R is at
ground.

No, you can't, because BAT is a device that is *defined* to have
a voltage potential difference across it of 10.1V . You cannot
arbitrarily choose to recognize and disregard this on a whim when
you analyze the circuit.

The voltage stated is a voltage *reference to ground*. One end of 1R
is + 10V above ground or the negative terminal that's for sure. But in
fact
the other side of 1R is *not* connected to ground at all through a zero
resistance, so there is not + 10V across R1. This shows how careful one
must
be when associating a zero resaistance value to some ideal component. I
must
be careful in doing that.

What's to be careful about? The circuit plainly shows the 1R resistor
connected to the battery + terminal at one end, and R1 at the other.
Nowhere in sight is there a hint of a direct connection of the 1R
resistor to ground (which by common convention is taken to be the
negative terminal of the battery for a simple circuit like this).



+-----------+--- 10V
| |
| [R1]
[1R| |
| |
| |
[BAT] [R2]
| |
| |
+-----------+
|
GND

But, when I drew the circuit, BAT and 1R is an equivalent circuit for a battery. Consisting of a perfect battery (BAT) and an internal resistance (1R).

Face value you want to say, hey if BAT is a perfect battery with zero resistance, there's 10V across 1R. Of course that is not true. It's just one of these issues you get when dealing with perfect components in series with resistance. 10v is just a statement that that point is 10V above a refrence point. And there really is not a zero resistance across BAT. It's mixing a fiction with reality. The equivalent circuit of a batttery is a fiction.

.

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