In case you don’t know a diode is a small electrical piece that allows a current to run through it in one direction only (any body who has worked with or studied electrical symatics knows that this is very important), my question is , how can you do that without any moving parts. The one person I did ask (who seemed like someone who should know) replied “magic”

Formerly known as Nec3f on the AOL SDMB

Magic works for mee too, but who ever said that electrons weren’t moving parts?

The classical diode is a junction of two bits of differently “doped” semiconductor (doping is an introduction of impurities, atoms with free electrons or “holes”). These are called N and P layers.

Basically, when you add more electrons to the layer with the free electrons, these can cross over to the “holes” with little resistance. But when you reverse current, and draw the free electrons away from the free electron layer, that layer becomes depleted an the junction loses its conductivity.

For those of us who are not electrical engineers, Jens meant to say: Diodes belong to the species called semiconductors because their conductivity swing from very conductive (offering almost no resistance to the flow of electrical current) to not very conductive (behaving like a virtual insulator). Whether they are conductive or not (or somewhere in between) depends on how the batteries are put into your transistor radio, or whatever. That’s why you have to observe polarity when reloading your remote control. The best analogy I can think of for what’s actually going on inside of the little bugger is to think about 2 magnets. When the orientation is wrong, they repel each other and there is dead air space between them. Turn one of them around and they snap together, making contact. The former state is analogous to the insulating state, the latter to the conductive state. Of course in a semiconductor diode there is no empty space as there is in a vacuum tube diode- they are made of solid material (which gave rise to the term “solid state”).

If you need to know any more, sign up for a course in semiconductor physics at your local trade school.

As far as I know, electrons aren’t moving parts, at least not in the sense that a flow of electricity is electrons moving from one place to another. Or did I misunderstand my basic electricity course?

Electrons are indeed moving objects. They move at almost the speed of light as they orbit the nucleus of the atom around which they reside.

Sorry, but I can’t think of any way to simplify the following… Nick made me do it.

Electrical current is due in part to those electrons which aren’t held as securely in their orbits and can be easily “broken away” with some externally applied force. The most common force used to achieve this is electromotive force (emf), which is the textbook term for voltage. Other kinds of force that can cause loosely held electrons to break free and be used as current carriers are:

Light (as in photocells)
Heat (as in thermistors- heat sensitive resistors)
Pressure (as in crystals)
Magnetism (as in most generators)
Chemical (as in chemical dry cells)

The kinds of materials that exhibit this “loosely held electron” quality are mostly metals, which is why they are so well known for their conductive properties. On the other foot, insulators have all of their electrons held in place very securely (scientists think with Velcro), and therefore will not support the flow of electrical current.

Umm… Opus? I know what an electron is, and what it doesand does not do. Electrons do not “flow” through a wire like water flows through a river. Nor do they race around an electrical circuit like Sterling Marlin at Daytona. Nor does electron X blast off from power plant XX and wind up in my hair dryer along with his brothers and sisters. In the case of alternating current, the polarity reverses 60 times per second, and those electrons are not “flowing” anywhere. Electricity does not necessarily consist of electrons at all, for that matter, it can be propagated through charged atoms.

Fyi, that “loosely held” electron you ascribe to metals is not loosely held at all, it’s a free electron in a sea of free electrons. Niether is an electrical current “carried” by electrons.

And just as a footnote - any substance will conduct electricity if the voltage is high enough.

I’m no electrical engineer, but it seems as if you should get your facts straight before you start lecturing me about the properties of electrons in particular and electricity in general.

Well, yes and no, Nickrz. If I am understanding my engineering physics book correctly, free electrons are ‘loosely’ held by the metal atoms the surround, mind you they are so weakly held that no one atom can really be said to ‘hold’ the electron.

[A metal atom, such as copper, contains one or more outer electrons, which are weakly bound to the nucleus. When many atoms combine to form a metal, the so-called free electrons are these outer electrons, which are not bound to any one atom. These electrons move about the metal in a manner similar to gas molecules moving in a container.][Physics for Scientists and Engineers, 3rd ed. Serway. pg 631.]

So it could be said to be loosely held.

Also, not to sound pedantic, but 50Hz is the European standard for alternating current if I remember correctly.

I wonder what kind of voltage would be needed to force a charge across neutronium. :slight_smile:

[Note: Am an Engineer who is more concerned with the logical aspects of semiconductor gate construction and the debugging thereof, and I am moderately rusty on electrical physics at the moment.]

>>while contemplating the navel of the universe, I wondered, is it an innie or outie?<<

—The dragon observes


A “classical” diode is a vacuum tube with no grid. Electrons flow from the (thermally) hot cathode to the (thermally) cold plate, but not the other way around.

The exact workings of solid-state devices require an understanding of quantum theory and the matching math, but the stuff above is a good start.

And, yes, electrons flow. Current is measured in amperes, and amperes are coulombs per second, and coulombs are units of charge. The fact that AC reverses itself has nothing to do with it.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

Some of the women at work had one of those home parties where you could buy lingerie, body oils, and diodes. oh wait a minute…sorry

Nickrz wrote:

I think you’re confusing the basic concept of electric current with a peculiarity of AC. In a DC circuit, electrons definitely do flow from one place to another. They leave the negative terminal of the battery, move through the metal connecting wires, and arrive back at the positive terminal of the battery.

In your statement about the power plant, you’re mostly correct; electrons in an AC circuit do not flow through wires like water through pipes. But the oscillating charge does make electrons move inside the wires. It’s just that they constantly change direction, moving a small distance north (for instance), then a small distance south, and thus remain in mostly the same place.

The emphasis in the above is mine. While technically true, the statement is misleading.

Electric current is defined as a movement of charged particles. So by definition, you could create a current by simply moving ions around. But ions cannot move through a wire, and cannot be used to power electric appliances like computers or toasters or even light bulbs. So that would not be electricity as we usually think of it.

Well, in the 4 semisters I took of Semiconductor Physics, we started with the Scrheodinger wave equation and 2 years later arived at the diode equation. The mathimatic derivation was layed out in gruesome detail.
Why does chrage flow one way and not the other?
Applying the voltage in a forward bias exponetially increases the conductivity of the diode, reverse, exponentialy decreases the conductivity.

Why does it do that?
Mostly due to the FM principal.

What does FM stand for?
F&*king Magic.

Wasn’t that easier that wasting 3hours a week for 2 years in a classroom spout about electron density pinning?

[Insert Clever Quote Here]

Nick, it was not my intention to lecture you. You asked a question, and I answered. No need to strike such a defensive posture & shake your finger at me like that.

While some textbooks don’t even agree on the direction of current flow, all seem to agree that it certainly does flow in different mediums, assisted by or consisting of (depending on which book you pick up) some type of carrier. The popular vote: electrons. My colleagues & a few professors I have checked with at UMD engineering division assure me that no new Earth-shattering insights have turned up since I studied the subject, and since your question was with regard only to “basic electricity”, these explanations are sufficient.

Yes, you are right, Opus, and I apologize.
I have no excuse other than working on a 100 Mhz laptop with 8 Mb RAM and a 28.8 modem helped drive me a little crazier than usual.

Benjamin Franklin guessed wrong. He knew that electricity came in two kinds that flowed from one to the other, and decided to call one + and the other -.

Until about 100 years ago, it was assumed that current went that way. Electrical engineers using that theory made generators and motors and telegraphs and telephones and light bulbs that worked just fine. It was only around the turn of the century that the electron was discovered, and had to be given a - charge.

Electrical engineers still pretend that current flows from + to -, even though they know it doesn’t really. It works for them, and it is felt that screwing with the system could cause major safety hazards.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

Getting back to diodes a moment, I just wanted to throw in that current can flow both ways through a diode. All diodes have what is called a “breakdown voltage”. Basically, if you put a big enough potential difference across a diode in the reverse direction it will allow a current flow.

A special case, of course.