Re: Explanation of Amps

From: John Popelish (jpopelish_at_rica.net)
Date: 01/16/05 

Date: Sun, 16 Jan 2005 15:00:51 -0500

tuxtlequino wrote:
>
> Wow guys, thank you very much for explaining everything so quickly and
> in such a maner that it finally makes sense. Everybody apported
> something new to help me understand Amp's. Part of my problem
> understanding Amps had to do with the common knowledge out there. Most
> of what I heard was as a little child being warned by his father, or
> asking a silly question to an electrician. I heard many times that what
> kills is not Voltage, but Current.

There is a way of thinking about this that makes sense. If you touch
a source of voltage (with respect to the Earth, let us say) but you
are not also touching the Earth, your body potential rises to match
the potential of what you are touching, but, since there is no path
for current to leave your body through a second point, you will not
receive a shock.

Grab the water faucet with the other hand, and that potential will
drive current through you on its way to ground, and you will be
shocked by the current passing through you. But it was the voltage
difference between the two things you touched that pushed that current
through you.

> I also remember about how much static electricity we can accoumulate
> and discharge (I used to get shocked everytime at my College's
> library). So, through common sense I reached the conclussion that a
> certain amount of Amps was storaged at the batteries(or cells). When I
> first started to read the book in basic electricity and electronics my
> common knowledge made everything harder to understand. Now I know that
> everything has a certain resistance (and I supposed that is why a
> lighting can kill us, since we offer resistance).

Wrap yourself in metal, and the lightning will mostly choose that
material and avoid you almost completely.

> And knowing that
> batteries have current ratings explain why a car batery is more
> dangerous than another one.

A car battery does not produce enough voltage to push a dangerous
current through your skin resistance (though it will give your tongue
an unpleasant sensation). But it is dangerous because of the energy
it can release into a low resistance load that will get hot enough to
burn you. You can weld metal with a car battery.
 
> More questions will come as I learn more, but thank you for helping me
> with my questions about Amperes.
>
> I think I know that what Milles was trying to explain is that since
> every batery has a different resistance, they will have a certain
> amount of amp's (although not significant enough!).

It will have a short circuit current limit that occurs when its
internal voltage is all used up across its internal resistance.

> What I will like to
> know is how does the electrical companies carry electricity from far
> places. I mean, they have to fight all the resistance from the long
> cables, so the voltage has to be greater, and therefore we will have a
> very good amount of Amps in the lines. Does our AC electricity comes
> with Amp's?, or they are somehow wasted at the transformers?

About half of all the electrical energy that is generated is lost
heating the resistance of the distribution grid. They jack the
voltage up very high, since doubling the voltage allows the same power
(volts times amperes) to be delivered with half the amperes. And half
the amperes drops half the voltage across a given piece of wire
resistance. This reduces the wire losses to 1/4. Etc. But there are
practical limits to how high they can raise the voltage. Stand under
any high tension transmission line, and you can hear the crackle of
corona discharge taking place, draining energy from the wires.

> Sorry about the silly questions. I am a computer programer, so if you
> have questions about your computer I can help, but my knowledge in
> electricity is very limited.

But increasing. 

-- 
John Popelish

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