electric current

[Smart $]

I dont know about that last comment....

Matt

A circuit requires only a difference in potential to conduct. If one end of the circuit is say +12 volts with respect to earth ground and the other end is +6 volts to the same reference, there is a potential of +6 volts across the circuit. Electrons will flow across the circuit in an attempt to equallize both ends. An example of positive to positive conductance. Of course how the electrons flow is dependent on the components of the circuit!

 

[hillbilly]

Equilibrium is the word. All things in the universe are constantly trying to acheive it. If they did, nothing and I mean nothing would ever move again.
My thesis for the day, thank you .
steve

 

[mpross]

The simple answer, eddy212, is neither. Current is measure of the flow of electrons (not "holes"... they do not move [by relative comparison], even in a destructive anode/cathode relationship).

I dont think there is a simple :smile: answer to this. Many people have argued this concept for years. I went through apprenticeship, and have spent the last three years studying electrical theory at an engineering university, and can see both sides of the argument. I can say that as an apprentice, and journeyman, I wanted to learn these fundamental concepts at a deeper level, and I ended up in school again.

I love working with the tools, but I also love the books too! I say this to any sparks out there considering the idea of going back to school. GO FOR IT! If you get the chance to go and do it, you wont regret it! Electricians have a great practical knowledge of electrical theory, and have an upper hand going into the introductory circuits courses in college. Also, I have been lucky enough to not have any loans. My contractor has kept me on the payroll, and let me work over breaks/holidays. If anyone has this option, it works perfect!

Anyone else ever consider going?

-Matt

 

[Smart $]

The people that continue to argue the concept(s) are the ones that fail to grasp the science. That is also why many continue to call it electrical "theory". Just the word "theory" itself implies ambiguity. Just look at how much of our society is based on electrical and electronic utilization, from microvolt to megawatt... and I'm supposed to believe that someone, someday is going to come along and disprove this so-called theory and have it all come crashing down around us!!!

Anyway, I'm glad to hear your hitting the books...

 

[charlie b]

Winnie: Here is where your description goes astray:

The sign of the force on an electron is equal and opposite to the sign of the force placed on an equal positive in the same circumstances.

But in your two examples, the circumstances are not the same. Your examples have the charges moving in different directions.

Now consider if the current were electrons flowing from right to left. The charge of the particles is reversed, the direction of travel is reversed, but the magnetic field is the same. The net result is that the electrons experience a force upward, and the 'top' side of the conductor is rendered more _negative_ than the bottom side.

The direction of travel is reversed AND the "sign" of the charge is reversed. A negative charge moving to the left will experience a force downwards, and the 'top' side of the conductor is rendered more positive than the bottom side.

That is the same condition that resulted from the "hole" moving from left to right. That is why I asserted that the Hall Effect sensor would not be able to distinguish a positive charge moving one way from a negative charge moving the other way.

 

[winnie]

Consider a single electron moving from left to right, along the X axis in the direction of increasing X. The magnetic field is directed along the Y axis. The cross product of the X and Y axis is the positive Z direction, but the electron is negatively charged so the acceleration of the electron would be in the negative Z direction.

To get the same current with a proton, it would have to move along the X axis in the direction of decreasing X; to get the same current with positive charges they have to move in the opposite direction as negative charges. With velocity in the negative X direction, the magnetic field in the Y direction, the cross product is in the negative Z direction, and since the proton is positively charged it will again be accelerated in the negative Z direction.

In both cases the net current is in the same direction (electron moving to the right, or proton moving to the left) and in both cases the charge carrier is being accelerated in the negative Z direction by the interaction with the magnetic field. Net result is that you can tell the polarity of the charge carriers by the 'hall potential' (voltage perpendicular to the current flow), which will change polarity for different charge carrier species.

I know with certainty that the polarity of the hall effect is one of the differences between type-N and type-P semiconductors.

-Jon

 

[mpross]

Hall Effect

Hall Effect

winnie,

I agree, except that it would be for a hole, and not a proton. Check out post #15 that I entered. This link is actually wrong with their directions!

mpross

 

[winnie]

That is one of the aspects of this whole discussion that I find strange and wonderful. I was specifically trying to enlarge the discussion of current to include particles moving in free space, and erred in not tying things back to current in conductors (or semiconductors).

In free space, you could have positive charges moving to the left, or negative charges moving to the right, and have the _same_ current.

In ionic solutions, you could have positive ions moving to the left, or negative ions moving to the right, and have the _same_ current.

In semiconductors, you could have positive 'holes' moving to the left, or negative electrons moving to the right, and have the _same_ current.

But what I find strange and wonderful is that 'hole' current to the left is really the aggregate effect of electrons moving to the right, yet it acts like a localized positive charge moving to the left. It is an experimental fact that P-type semiconductors have Hall voltages that look as though _positive_ charges are moving around, yet the only things that are actually moving around are electrons. (Of course, these Hall measurements could all be mass delusions; I've never made these measurements myself!)

-Jon

 

[mpross]

Type of material

Type of material

I think we are on the right track here. For different materials, conduction takes place by different phenomena. I agree that current takes place from any type of charge in motion, wherever it is.

Remember that in a semiconductor, the material/compound can be either doped p-type, or n-type. This is a case where a difference in conduction occurs. In a p-type material the "density of states" is completly different than that of an n-type material. Conduction can take place by the movement of holes, and this might not be related to the movement of electrons. When a hole combines with an electron, that pair is destroyed, in relation to conduction.

 

[Smart $]

...yet the only things that are actually moving around are electrons.

Quite true. But I believe you are overlooking the most critcal point here... and that is the point of reference. In order to measure the current of a "hole" moving to the left, your point of reference is the electron moving away from it to the right. Hence, from this perspective, the electrons are not moving!

 

[mpross]

Sense?

Sense?

eddy212,

sorry for all of this, but is your original Q answered?

mpross