Re: An Absolute Beginner With A Few Questions

On Tue, 13 Dec 2005 19:46:55 -0600, via <dnntk3$c9$1@xxxxxxxxxxxxx>,
"Pete Holland Jr." <peterg@xxxxxxx> spake thusly:

>Hey, everybody!

Hey!

1, 2) Doesn't matter.

>3) The next project is building a crystal radio, powered by radio waves.

Oh boy! I built one when I was about five, my older brother and I. I
didn't do any more serious experiments with electricity until I was
about 12 and plugged an 8ohm speaker into a wall outlet. Tesla would
have been proud.

>It mentions attaching a wire to a ground.

Oh boy again! Grounding is fun.

> Buying a shortwave antenna for
>simple experiments strikes me as overkill, and the pipes in my place are
>PVC plastic. Then I remembered my computer. The case that I attach my
>anti-static wrist strap to is a ground. Can I just attach the ground wire
>to the case of my computer (with the computer powered off, of course)?

Yes.

>Failing that, I was told that the negative terminal of a battery is
>considered a ground. Can I just wire it to that?

No. No terminal of a battery can be considered a ground until a
ground is attached to the terminal. For instance, communication gear
is typically attached to 48VDC batteries, with the POSITIVE terminal
grounded.

>4) What gives something the ability to be a ground, anyway? Just that it
>can readily absorb an electrical current? It seems to me that, if the
>computer case idea is workable, then as long as the voltage is small,
>almost any sizable metal object would make a sufficient ground.

A sizeable metal object that carries electrical current is best
described as a chassis, as in the chassis of a car or motorcycle,
which is commonly used as a RETURN PATH for electrical current.
GROUND is the term that is in common use, because Mother Earth is
extensively used as a return path for electrical currents.

Specifically in the case of your computer (double entendre?), the
chassis makes a ground because the chassis is connected to a prong on
the input power cable, which allows current to find real earth ground
through the house wiring.

Now, ground is a lot more complicated than most people in the various
electronics fields realize. One of the most useful and conversely
most incorrect concepts is that a common point on a schematic is "the
same point electrically." For theory that works great. In reality,
well, the reality is much different. It's like ignoring the effect of
wind and air resistance when doing falling body calculations. It
makes the math easier and teaches the concept, but actually has
precious little resemblance to the real world.

>5) Big question: I was taught in science class years ago the electricity
>actually flows from the negative terminal to the positive. Even though the
>book says the other way around and schematics for things like diodes imply
>power goes from positive to negative, when it gets to transistors, it says
>the electrical path is emitter to collector or emitter to base. Did they
>just mix the words up, since the schematic shows the flow going the other
>way, or am I missing something?

The topics of electron flow and energy flow are a big-assed can of
worms. Instructors blame Ben Franklin for misunderstanding the
direction of electron flow, but he actually had a good grasp of how
electrical energy flowed. (His "kite and key" experiments were
intended to figure out a way to protect dwellings from burning down
from lightning strike, and were a real success.)

Thus we have energy flow from positive to negative, whereas actual
electron flow is from negative to positive. In applied electronics,
energy flow is more important than electron flow. Here's a heads-up
for you - when you get to transistor theory and design, they'll throw
"hole flow" at ya. Yikes!

Good luck.

.

Relevant Pages

  • Traveling Wave Accelerator Coil Injector
    ... An excellent mathematical model that describes flow rate ... Traveling Magnetic Wave Interaction and Wave Growth: ... e = charge of electron ...
    (sci.space.policy)
  • Re: Traveling Wave Accelerator Coil Injector
    ... An excellent mathematical model that describes flow rate ... Traveling Magnetic Wave Interaction and Wave Growth: ... e = charge of electron ...
    (sci.space.policy)
  • Re: mobility of holes
    ... Just imagine for both type of devices, the current is due to electron flow, what actually happen in the mechanism of electron flow in pmos that required us to have a hole mobility? ... basically a matter of convention that people refer to electrons moving in the conduction band vs. holes moving in the valence band. ...
    (sci.engr.semiconductors)
  • Re: Injecting current into a cell
    ... Conventional current used to be taught as the flow of positive charge ... In other words, it didn't make any difference if the electron were flowing, ... In a cell containing an electrolyte the situation is a bit different. ...
    (sci.chem)
  • Re: Relation
    ... almost sits there and vibrates (thus exciting from one electron to the ... energy flow and vice-a-versa. ... know the amperes, wire diameter/radius, and how many moving electrons per ...
    (sci.electronics.basics)