Re: An Absolute Beginner With A Few Questions

Pete Holland Jr. wrote: 
Hey, everybody!

I figured the best place to get my feet wet was with one of those electronic
kits like Radio Shack sells.  Bunch of components, instruction manual,
compact size, 30 projects to get you rolling.

So I'm working on it and paying attention, and some questions are forming
(after just four projects, too.  I'm not sure if that's good or bad).

1)  In a simple light circuit, using an LED, batteries, and a resistor, does
it matter where the resistor is placed?  The book cautions that LED's can
burn out from too much power.  Does the resistor stay before the LED, can
it be placed after, or does it matter as long as one immediately follows
the other in series?

The same current passes through all components in a series loop, regardless of the order.

2) The kit features two..."regular" (I guess they might be called disc)
capacitors and two electrolytic capacitors. I noticed the schematics, when
they depict the electrolytic ones, include a positive symbol by the flat
line instead of the curved. So they can obviously only be connected in the
circuit one way, positive current to positive terminal on the capacitor. But what about the smaller disc ones? Does it matter for them?

No. They have ceramic insulation between their plates and it handles voltage in either direction, equally. The insulation between the "plates" of an electrolytic capacitor is formed by a chemical action between the internal liquid and one of the plates (a roll of aluminum foil that has been chemically etched to make it very porous, to have a huge surface area) driven by a DC voltage. I say "plates", because the other one is the liquid.

3) The next project is building a crystal radio, powered by radio waves. It mentions attaching a wire to a ground. 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)?

The case of the computer, and any other thing connected to the ground prong of a 3 prong AC receptacle should connect to ground. Of course, you could also drive a big nail into damp ground and run a wire inside from that.

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

No. Any point in a circuit may be considered a common node with which to measure other voltages, (and is commonly referred to as circuit ground), but it has nothing in particular to do with Earth ground. Current from an aerial has no incentive to flow in and out of a floating battery terminal.

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 planet sized mass will do fine.  ;-)

But seriously, you are right. Any metal object that is at least a quarter wavelength long in every direction from the connection point can act as ground for an aerial. But at approximately 1 megahertz (broadcast AM band) that is a pretty large object. At 27 MHz (citizens band) a car body is a fair ground for a quarter wave whip..

5)  Big question:  I was taught in science class years ago the electricity
actually flows from the negative terminal to the positive.

That would be electron (or any other current carried by negative charge carriers... Got any muons?)

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?

When Ben Franklin was experimenting with batteries, he assigned the polarities and guessed the current direction. He was right for protons, holes, positrons and positive ions. He had no idea what carries the current. And as long as you use one concept, consistently, the math all works out, though thinking about the current through electron tubes gets pretty silly using positive current. But for semiconductors (diodes and junction transistors, there are both positive and negative charge carriers in play, so either convention is half wrong. Just remember that a positive charge going one way is the same current as a negative charge going the other way.

Sincerely,
Pete Holland Jr.

.

Relevant Pages

  • Re: Basic Question
    ... matter of velocity of electron flow? ... lower hence you don't need wire as thick as the low side. ... velocity at higher voltage. ...
    (sci.physics.electromag)
  • Re: Basic Question
    ... matter of velocity of electron flow? ... lower hence you don't need wire as thick as the low side. ... velocity at higher voltage. ...
    (sci.physics.electromag)
  • Re: Basic Question
    ... matter of velocity of electron flow? ... wire by means of increasing the voltage. ... velocity at higher voltage. ...
    (sci.physics.electromag)
  • Re: Magnetic effects around electric currents and absurdities of modern physics
    ... each have a magnitude of charge equivalent to 1 electron. ... voltage between them is constant. ... current is the same in both conductors. ... The magnetic field in Maxwells ...
    (sci.physics.electromag)
  • Re: 1c+1c Closing Velocity...,answer to Henri Wilson
    ... assuming that the electron affinity is the right energy. ... energy thereof -- and that's where the voltage comes in. ... So, questions to all three of Eric Gisse, Androcles, and H.W.: ...
    (sci.physics.relativity)