Common Electrical misconceptions?

  • #1
Forgive me if I've fallen prey to random google searching but I was wondering if what this guy has to say has any bearing on reality. I know almost nothing about electrical engineering and something steered my surfing into that field so I happened upon the site.

It is supposedly a list of common misconceptions about electricity taught in schools. No need to commentary on his confusing and perhaps unprofessional communication style, I already noticed that and am unconcerned. Just curious if this is totally misleading, has some truth and some crap, or is totally correct presented in an odd fashion.

http://amasci.com/miscon/eleca.html#frkel

Thanks!
 

Answers and Replies

  • #2
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The article is totally true and brings out important facts. When Benjamin Franklin did his first experiments with electricity he reasoned that there are 2 charges + and - . He went further to say that one of the charges was always stationary while the other had to flow. He couldn't tell which one so he took a wild guess and said the + charges flow and - are stationary. Until 1900's J.J. Thompson did an experiment with a cathode ray tube and discoveter that the charge that flows is infact negative. Another noble peace price for him, but the damage has already been done. All the engineering community used Benjamins convection that + charges flow and use it in ther designs even to this day.
 
  • #3
Well I'll tell you one specific area that is kinda confusing to me is the flow of electrons actually being extremely slow.

I understand a wave of kenetic energy traveling across a medium still transmitting energy very quickly. That's fine. If I had a tube full of billiard balls a mile long and I started cramming new ones in at a rate of 1 per second, the flow of 'electrons' would be quite slow but the energy required to pop one out the other end would transmit very quickly.

Here's my problem:

If electrons travel rather slowly through a wire and the way in which electrical energy (pretty much kenetic) is transmitted always through a medium. Isn't a vacuum an absolute removal of medium required to transmit energy electrically? Perhaps it's just because I don't really understand the differences between conductivity, permittivity and permeability, but I thought I understood that vacuum has a greater than 0 permittivity.

Doesn't that mean that it is possible to transmit electrical energy across a vacuum? Are the individual electrons jumping the gap and traveling much faster than they would in a wire?
 
  • #4
Averagesupernova
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I didn't take alot of time to read through that site. Most of it looks legit. But the author has some misconceptions of his own. Bill Beaty in the past has been a big free energy nut. Yep, you guessed it, perpetual motion.
 
  • #5
hehe a bit off the wall eh?

Well can anyone answer my question in my second post for me?

Thanks!
 
  • #6
Cliff_J
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Start by thinking about the voltage required for lightning to occur, the air is an extremely poor conductor (else we'd never have open circuits!) but the air is still able to conduct at those levels. Not an answer, that's more just changing the medium the charge is sent over, you're asking about removing the medium completely.

Someone will correct if I'm off here but electricity requires matter to flow - the electrons are going from one atom to the next of the conductor. And a vacum would be an absence of matter, so with no matter present there would be no electrons available to flow.

Now convert the electricity to some form of electromagnetic wave and its a different story.
 
  • #7
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Cliff_J said:
Someone will correct if I'm off here but electricity requires matter to flow - the electrons are going from one atom to the next of the conductor. And a vacum would be an absence of matter, so with no matter present there would be no electrons available to flow.

This seems right to me.

However I think it should be pointed out electrons, and thus electricity, can exist independently of atoms (for instance in an electron beam http://physics.nist.gov/MajResFac/EBIT/intro.html). Notice the beam has both current (basically the number of electrons passing a point per second) and voltage (basically the number of electrons in one place compared to another).

I think one should be able to transmit electrical energy across a vacuum. Give the electron some momentum, then electron enters the vacuum and pops out the other side some time later. Although I guess technically, while the electron is in transit, the space is not a vacuum...
 
  • #8
NoTime
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egsmith said:
Although I guess technically, while the electron is in transit, the space is not a vacuum...
There is tunneling as well.
First the electron is at point A then it is at point B.
Transit doesn't seem to apply.
 
  • #9
Averagesupernova
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Has everyone here forgotten about vacuum tubes? Electrons are 'boiled' off of the cathode by thermionic emission. They form a sort of cloud around it. With the proper voltages on the plate (anode) and cathode we form a current through the vacuum. So technically electrons need NO medium to travel through. Of course we don't build our circuits out of 'nothing' so we end up with WHAT I THOUGHT was the familiar vacuum tube with electrons jumping between 2 conductors through space. Any material that gets in the way, such as air, will impede the flow of electrons and that means no more current.
 
  • #10
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Averagesupernova said:
Has everyone here forgotten about vacuum tubes?

Actually I had. :rolleyes: Great example though.

Now that I think about it, a CRT contains a vacuum as well. Probably not a perfect one though.
 
  • #11
Averagesupernova
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egsmith said:
Actually I had. :rolleyes: Great example though.

Now that I think about it, a CRT contains a vacuum as well. Probably not a perfect one though.

No vacuum is perfect. A CRT is highly evacuated though. That electron has a LONG way to go from the gun to the phosphor when you consider its size. Therefor very little can be allowed to get in the way.
 
  • #12
Ouabache
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waht said:
When Benjamin Franklin did his first experiments with electricity he reasoned that there are 2 charges + and - . He went further to say that one of the charges was always stationary while the other had to flow. He couldn't tell which one so he took a wild guess and said the + charges flow and - are stationary. Until 1900's J.J. Thompson did an experiment with a cathode ray tube and discoveter that the charge that flows is infact negative. Another noble peace price for him, but the damage has already been done. All the engineering community used Benjamins convection that + charges flow and use it in ther designs even to this day.

That always bugged me.. I learned early on in chemistry and physics that electrons are the particles that move from orbital to orbital within an atom, and highly energetic ones can leave an atom, leaving a positive ion in its wake. If that free electron comes upon another positive ion that is missing an electron, the electron would be attracted to it and fill that orbit balancing the charge and creating a neutral atom. Then I get to electrical engineering, and find current defined in terms of the flow of holes (atoms missing an electron). Seemed abit silly to carry on that idea. Though it is often rationalized that a net movement of electrons in one direction can be equated to a movement of holes in the opposite direction.


Regarding his other thoughts, it looks to me that he is just being picky about choice of wording.
 
  • #13
Cliff_J
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Ok, I'll stand as corrected as technically that is true.

But if we remove the heat and the edison effect is gone then no electron flow occurs as would in any other matter, correct? As in regardless of buildup stored on the plate, electrons wouldn't jump the gap without the thermonic emission, right? Or does that even occur at room temperatures?

(sorry, tubes were a little before my time and now it seems they are only used as fodder in some sort of sonic attribute debates between solid-state and tube affectionados)
 
  • #14
Averagesupernova
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Not sure cliff but I think there are some tubes that have no filament. I believe they were used as high voltage rectifiers. They may have been gas filled. Have to research this.
 
  • #15
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Averagesupernova said:
Not sure cliff but I think there are some tubes that have no filament. I believe they were used as high voltage rectifiers. They may have been gas filled. Have to research this.

Yes, these do exist and are called cold cathode tubes. They are filled with a low pressure gas (Nobel gasses) and operate by avalanche. CC Tubes operate in a manner very similar to semiconductors.In fact, I believe the old Nixie tubes where cold cathode as well. Need to look that up myself.
 
  • #16
NoTime
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Yep, Nixie tubes are cold cathode. No different than a neon lamp except for the multiple electrode structure works as a display.
 
  • #17
SGT
Cliff_J said:
Ok, I'll stand as corrected as technically that is true.

But if we remove the heat and the edison effect is gone then no electron flow occurs as would in any other matter, correct? As in regardless of buildup stored on the plate, electrons wouldn't jump the gap without the thermonic emission, right? Or does that even occur at room temperatures?

(sorry, tubes were a little before my time and now it seems they are only used as fodder in some sort of sonic attribute debates between solid-state and tube affectionados)

The cathode, being made of a metal, has plenty of free electrons on it. Those electrons are bound in the material of the cathode by the attraction of the charged nuclei, but if you give them enough energy, they can leave the material.
The easiest way to provide energy to the material is by heating it. That is why we heat the cathode. But you can provide energy by keeping the cathode in a strong enough electric field.
So, if the anode and the cathode are close enough and have a great potential difference between them (anode positive with respect to cathode), electrons can leave the cathode and jump to the anode, even in absolute vacuum.
 
  • #18
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The originial question here was actually whether electrical "energy" could be transmitted through a vacuum. And you don't need electrons or cathodes for that. Electromagnetic induction works fine, and it DOES travel at the speed of light.
 
  • #19
jdavel said:
The originial question here was actually whether electrical "energy" could be transmitted through a vacuum. And you don't need electrons or cathodes for that. Electromagnetic induction works fine, and it DOES travel at the speed of light.

I guess I might have stated the question wrong. I didn't mean EM induction.

Basically I was meaning that even aside from electron clouds produced in a variety of items, it is my understanding that electrical permittivity of a vacuum is 1 and other mediums are given values related to that. The problem I have with that is that it is not 0. This seems confusing because it seems as though this is saying that electrons will jump across a vacuum gap if there is enough potential or whatever. (plz excuse my ignorance)

Can any of you answer what is meant by electrical permittivity of 1 instead of 0? I'm pretty sure that's a known and accepted constant but it seems I'm missing something.
 
  • #20
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TheAntiRelative said:
I guess I might have stated the question wrong. I didn't mean EM induction.

Basically I was meaning that even aside from electron clouds produced in a variety of items, it is my understanding that electrical permittivity of a vacuum is 1 and other mediums are given values related to that. The problem I have with that is that it is not 0. This seems confusing because it seems as though this is saying that electrons will jump across a vacuum gap if there is enough potential or whatever. (plz excuse my ignorance)

Can any of you answer what is meant by electrical permittivity of 1 instead of 0? I'm pretty sure that's a known and accepted constant but it seems I'm missing something.

Electric permittivity has nothing to do with electric current. Electric permittivity is introduced in Coulomb's law in order relate force to charges and distance. The permittivity of vacuum ε0 is 8.85x10-22 F/m and not 1. The dielectric constant is the quotient of the permittivity of a medium and the permittivity of the vacuum. Of course, the dielectric constant of the vacuum is 1.
 
  • #22
SGT said:
Electric permittivity has nothing to do with electric current. Electric permittivity is introduced in Coulomb's law in order relate force to charges and distance. The permittivity of vacuum ε0 is 8.85x10-22 F/m and not 1. The dielectric constant is the quotient of the permittivity of a medium and the permittivity of the vacuum. Of course, the dielectric constant of the vacuum is 1.

What is the purpose/use of relating force to charges and distance then. What is the permittivity of a medium used for. What does it tell us?

Is the permittivity of the vacuum kind of an imaginary concept or something?
 
  • #23
SGT
TheAntiRelative said:
What is the purpose/use of relating force to charges and distance then. What is the permittivity of a medium used for. What does it tell us?

Is the permittivity of the vacuum kind of an imaginary concept or something?

From Coulomb's law, the electrostatic force between two charges q1 and q2 is:

F = k.q1 .q2 /d2

Where k is Coulomb's constant k = 1/4.π.ε0

The 3 constants concerning electric and magnetic fields propagation are the speed of light in a vacuum: 3.108 m/s, the magnetic permeability of free space: μ0 = 4π.10-7 and the electric permittivity of free space ε0.
They are related such that c = 1/sqrt(μ0ε0). This sets the value for ε0.
 
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  • #24
chroot
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SGT said:
k is chosen such as if both charges are 1 coulomb and the distance between them 1 meter, the force must be 1 newton.
This is quite false! The force between two one-coulomb charges one meter apart is almost ten billion newtons.

- Warren
 
  • #25
SGT
chroot said:
This is quite false! The force between two one-coulomb charges one meter apart is almost ten billion newtons.

- Warren

I have already corrected that.
 

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