Analogies- are they correct?
- Thread starter peter d
- Start date
- Status
physis
Senior Member
Re: Analogies- are they correct?
First, let me claim ignorance.
I don't remember everything about valence and electron shells. I used to know the number of electrons per shell.
Anyway, mostly you're transmiting a charge across the conductor. You push on the electrons. They push on the next. What you are pushing on on the other end (or more accurately, in the middle), for more than one reason, pushes back. The electrons don't do that much moving. But being pushed, they will sometimes be displaced from one atom to the next. I start to loose it here but I think it's that the outer shell of conductors are either more likely or more capable of holding or realesing extra electrons.
I don't remember. Is it that the atoms have covalent bonds, where two atoms will share an electron in orbit around both of them, the electron sort of doing a figure eight around them both but still making both outer shells happy?
I missed this one earlier Crossman.
First, let me claim ignorance.
I don't remember everything about valence and electron shells. I used to know the number of electrons per shell.
Anyway, mostly you're transmiting a charge across the conductor. You push on the electrons. They push on the next. What you are pushing on on the other end (or more accurately, in the middle), for more than one reason, pushes back. The electrons don't do that much moving. But being pushed, they will sometimes be displaced from one atom to the next. I start to loose it here but I think it's that the outer shell of conductors are either more likely or more capable of holding or realesing extra electrons.
I don't remember. Is it that the atoms have covalent bonds, where two atoms will share an electron in orbit around both of them, the electron sort of doing a figure eight around them both but still making both outer shells happy?
izak
Senior Member
- Location
- Springfield, MO
Re: Analogies- are they correct?
I wonder....
I have been taught that the 'electrons' do not actually 'travel' through the wire.....
they travel AROUND it
after i was taught that, i remembered something from when i was about 13 years old...
the desert of southern California is VERY prone to electrical storms... the kind that turn night into day...
one night we were watching the lightning, like ususal, and saw lightning hit a power line, about 3 miles from our house....
it was your typical, 7200/13800 three phase primary line, and what i remember is that the 'lightning bolt' traveled down that line (towards my house) in a HUGE spiral, like about 2 feet or more in diameter... you could see where it reached each pole because it went to ground on the wood and blew up the insulators in a giant shower of sparks...
seemed like it traveled for about 3 miles....
it was a trip
I wonder....
I have been taught that the 'electrons' do not actually 'travel' through the wire.....
they travel AROUND it
after i was taught that, i remembered something from when i was about 13 years old...
the desert of southern California is VERY prone to electrical storms... the kind that turn night into day...
one night we were watching the lightning, like ususal, and saw lightning hit a power line, about 3 miles from our house....
it was your typical, 7200/13800 three phase primary line, and what i remember is that the 'lightning bolt' traveled down that line (towards my house) in a HUGE spiral, like about 2 feet or more in diameter... you could see where it reached each pole because it went to ground on the wood and blew up the insulators in a giant shower of sparks...
seemed like it traveled for about 3 miles....
it was a trip
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Analogies- are they correct?
In a wire, once you connect the voltage source, an electric field is called into existence throughout the length of the wire. Every electron feels a push at the same time. It is the field that does the pushing, it is not each electron pushing the next one in line. You are right in stating that only the outer shell electrons are free to move. Every electron, and even the protons in the center of every atom, will feel the push from the electric field. But the field is not strong enough to kick loose all of the electrons, and it is way way too weak to kick loose any protons. Depending on the strength of the source (i.e., the voltage level), some number of the outer shell electrons will respond to the push, and will start jumping from atom to atom.
The reason Ohm?s Law works the way it does is this: If you double the voltage, you do not make the electrons move faster. Instead, the stronger push is able to make twice as many electrons jump away from their host atoms, and start moving along the line.
That is a reasonable way to look at it. Any one given electron (let?s call it ?George?) may make a jump from one atom (the ?first atom?) to the next atom (the ?second atom?). It may stay there a while. A different electron that had been circling this atom (let?s call this one ?Tom?) might make a jump to the next atom (the ?third atom?). As time goes on, George and Tom will slowly make their way down the wire. Their speed of progress will be on the order of inches per minute (or perhaps it is inches per second). However, an observer looking at the whole wire will not be able to distinguish George from Tom from any other electron. All the observer will see is that a bunch of electrons are passing by the point of his observation, and that they are doing so at very nearly the speed of light.
This is where one of the more commonly-used mechanical analogies falls short of reality. In a garden hose, each molecule of water is pushed along the hose by the molecule behind it. The water at the sprinkler head does not move, until the push has made its way, molecule by molecule, from the pressure source, through the house?s pipes, into the beginning of the hose, and all along the hose. Not so for electrical currents. This is one of the ?elegant? ways in which electric flow differs from water flow.
In a wire, once you connect the voltage source, an electric field is called into existence throughout the length of the wire. Every electron feels a push at the same time. It is the field that does the pushing, it is not each electron pushing the next one in line. You are right in stating that only the outer shell electrons are free to move. Every electron, and even the protons in the center of every atom, will feel the push from the electric field. But the field is not strong enough to kick loose all of the electrons, and it is way way too weak to kick loose any protons. Depending on the strength of the source (i.e., the voltage level), some number of the outer shell electrons will respond to the push, and will start jumping from atom to atom.
The reason Ohm?s Law works the way it does is this: If you double the voltage, you do not make the electrons move faster. Instead, the stronger push is able to make twice as many electrons jump away from their host atoms, and start moving along the line.
Ed MacLaren
Senior Member
Re: Analogies- are they correct?
For a more common example, in a fluorescent lamp, electrons are emitted from one end filament and flow through the ionized filling gas to the other end filament.
Ed
[ January 20, 2005, 09:04 PM: Message edited by: Ed MacLaren ]
Yes, the cathode of vacuum tubes are coated with certain chemical compounds that readily "emit" electrons, (edit) but they are "collected" and still end up flowing back to their source.
For a more common example, in a fluorescent lamp, electrons are emitted from one end filament and flow through the ionized filling gas to the other end filament.
Ed
[ January 20, 2005, 09:04 PM: Message edited by: Ed MacLaren ]
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Analogies- are they correct?
Charlie, I don't understand your analogy. Are you saying Tom and I are slow, or we tend to get pushed around?
Charlie, I don't understand your analogy. Are you saying Tom and I are slow, or we tend to get pushed around?
crossman
Senior Member
- Location
- Southeast Texas
Re: Analogies- are they correct?
In the cathode ray tubes and florescent lamps, wouldn't it be safe to say that the electrons are still traveling through a conductor? Doesn't the gas in there become ionized to the point that it becomes conductive and the electrons are simply traveling towards the positve side of the source through a complete circuit?
In the cathode ray tubes and florescent lamps, wouldn't it be safe to say that the electrons are still traveling through a conductor? Doesn't the gas in there become ionized to the point that it becomes conductive and the electrons are simply traveling towards the positve side of the source through a complete circuit?
crossman
Senior Member
- Location
- Southeast Texas
Re: Analogies- are they correct?
Concerning the analogy:
On the "push-pull" description of electricity, wouldn't a pump with a closed piping system as a circuit resemble the "push-pull" action of a voltage source?
And does anyone have a link or source or recommended reading material on the "speed of electrons through a conductor"?
Concerning the analogy:
On the "push-pull" description of electricity, wouldn't a pump with a closed piping system as a circuit resemble the "push-pull" action of a voltage source?
And does anyone have a link or source or recommended reading material on the "speed of electrons through a conductor"?
Ed MacLaren
Senior Member
Re: Analogies- are they correct?
Now just wait. Someone will bring up a "flashover" across or through an insulator.
Ed
Yes. If it wasn't a conductor they couldn't flow.
Now just wait. Someone will bring up a "flashover" across or through an insulator.
Ed
physis
Senior Member
Re: Analogies- are they correct?
I wont say lightning Ed.
What I meant was that the field of each electron pushes against the next electron's field.
There is, I'm sure, a law for this. It has to do with the "need" for like charges to be evenly distributed.
I wont say lightning Ed.
If you didn't have to contend with "C" your statement would be true.
What I meant was that the field of each electron pushes against the next electron's field.
There is, I'm sure, a law for this. It has to do with the "need" for like charges to be evenly distributed.
caosesvida
Senior Member
Re: Analogies- are they correct?
Electrons do move down the wire, but that is not the major part of what is going on. IT is the the energy that is moved along the wire, by transfering from shell to shell of the copper.The eneregy is transfered, till we get to a device that transforms one form of energy to another, ie. electrical energy to magnetic energy. I forget the exact number of electron movement, but it is very slow(relative to the energy movement). That is where the water theory falls short for me. Water is matter, we want electrical energy, so they are completely different. Voltage to me is not like presure in a water hose, this creates the illusion that electrons are flying out of the outlet. Its always a difference of potential, more here less there, and wants to equalize. The little balls theory is also misleading in this, I look at it as more of a cloud or blur. anyway thats my take on it.
Electrons do move down the wire, but that is not the major part of what is going on. IT is the the energy that is moved along the wire, by transfering from shell to shell of the copper.The eneregy is transfered, till we get to a device that transforms one form of energy to another, ie. electrical energy to magnetic energy. I forget the exact number of electron movement, but it is very slow(relative to the energy movement). That is where the water theory falls short for me. Water is matter, we want electrical energy, so they are completely different. Voltage to me is not like presure in a water hose, this creates the illusion that electrons are flying out of the outlet. Its always a difference of potential, more here less there, and wants to equalize. The little balls theory is also misleading in this, I look at it as more of a cloud or blur. anyway thats my take on it.
Ed MacLaren
Senior Member
Re: Analogies- are they correct?
Also, I don't know how to draw a "blur".
Ed
Yeah, me too, but it would have been hard for the little guy in my sketch to get hold of "clouds" and throw them.
Also, I don't know how to draw a "blur".
Ed
crossman
Senior Member
- Location
- Southeast Texas
Re: Analogies- are they correct?
Another thought:
An open circuit is actually capacitance, isn't it? Now it may very well be an extremely small value of capacitance, but it is indeed capacitance.
Another thought:
An open circuit is actually capacitance, isn't it? Now it may very well be an extremely small value of capacitance, but it is indeed capacitance.
crossman
Senior Member
- Location
- Southeast Texas
Re: Analogies- are they correct?
Hmmm.... looks that way from here!
er... infinite frequency will reduce any open circuit to conductance? Yikes! Infinite frequency would electrocute all of us!
Nevermind, I am just babbling, but I will stand in my statement that any open circuit is actually capacitance.
Hmmm.... looks that way from here!
er... infinite frequency will reduce any open circuit to conductance? Yikes! Infinite frequency would electrocute all of us!
Nevermind, I am just babbling, but I will stand in my statement that any open circuit is actually capacitance.
- Status