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A question about frequency…

  1. Feb 5, 2009 #1
    The ordinary AC house-hold supply of 60Hz has a wave-length of about 5 x 10^6 m.

    With a frequency of 60 hz the alteration of the signal is
    going from 0 Volts, to Full Volts+, back to 0 volts, then Full Volts-,
    and then back to 0 volts to complete a full cycle 60 times per second.

    Is it the entire copper molecule shaking back and forth 60 times per second?

    Is it that the electrons are orbiting around the nucleus for one full orbit and then reversing the orbit to the opposite direction over and over 60 times a second?

    Is it that only the free unpaired electrons are shaking back and forth from left and right inside the copper wire and that’s what it means when you say the signal is going from 0 Volts, to Full Volts+, back to 0 volts, then Full Volts-, and then back to 0 volts to complete a full cycle?

    What exactly is happening 60 times per second??????????
     
    Last edited: Feb 5, 2009
  2. jcsd
  3. Feb 6, 2009 #2

    clem

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    Yes..............
     
  4. Feb 6, 2009 #3

    berkeman

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    The AC generator at the power station is generating an AC voltage that has the frequency of 60Hz (Hz = cycles per second). That voltage is put across the power lines, and that voltage causes an AC current to flow in the wires. You are correct that the wavelength is quite large for such a low-frequency transmission line waveform.

    The electrons that are moving back and forth are in the conduction band of the metal wire cables of the electrical transmission line. The electrons actually don't move very far back and forth -- I haven't calculated it for 60Hz and transmission line currents, but it's probably only a meter or so back and forth. But each electron influences its neighbor in the conduction band, so they end up all moving back and forth as the AC current that is pushed into the transmission line at the source by the generator.

    That explanation is a bit simplified, but hopefully it helps to start answering your question. Here's a link that may also provide you with more background and links to further reading:

    http://science.howstuffworks.com/electricity1.htm

    .
     
  5. Feb 6, 2009 #4
    OK a New Question that starts out the same way...

    A question about wave-length...


    The ordinary AC house-hold supply of 60Hz has a wave-length of about 5 x 10^6 m.

    With a frequency of 60 hz the alteration of the signal is
    going from 0 Volts, to Full Volts+, back to 0 volts, then Full Volts-,
    and then back to 0 volts to complete a full cycle 60 times per second.


    Only the free unpaired electrons are shaking back and forth from left and right inside the copper wire and that’s what it means when you say the signal is going from 0 Volts, to Full Volts+, back to 0 volts, then Full Volts-, and then back to 0 volts to complete a full cycle.

    The wave-length is about 5 x 10^6 m.

    Dose this mean that the unpaired electrons in the copper wire are shaking back and forth over a distance of 5 x 10^6 m?????
     
  6. Feb 6, 2009 #5

    clem

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    No. For instance, when a string vibrates, the particles on the string move up and down a small distance, unrelated to the wave length.
     
  7. Feb 6, 2009 #6

    berkeman

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    And to add a bit to clem's comment...

    Consider a taut rope that runs off into the distance, and you are holding onto one end of it. If you start shaking your end up and down, a travelling wave is launched down the string. After a bit of shaking, the travelling wave can be quite a ways down the string. The vertical oscillations at some distance down the string are the result of the initial oscillations back at your hand, but the rope pieces (like the electrons in your question) are not directly infulenced by your hand. They are influenced by the local pieces of rope that are adjacent to them, and the motion of those local pieces is what causes the local motion.

    The travelling wave "propagates" down the rope, just as the AC voltage and current waveforms propagate down the electrical transmission line. Does that help?
     
  8. Feb 6, 2009 #7
    OK if 5x10^6m is not the distance traveled by free electrons moving back and forth then what is it the distance of?
     
  9. Feb 6, 2009 #8

    berkeman

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    The wavelength on the transmission line. You're making this harder than it is. Think about higher frequency, shorter wavelength transmission lines. Like 300MHz on 300 Ohm stripline coming down from your TV antenna on your roof. 300MHz RF has a wavelength of 1 meter in free space, and close to that on 300 Ohm stripline cable.

    The distance 1m is the wavelength of the RF travelling wave at 300MHz that is coming down from the antenna into your TV set. If you could measure the differential voltage at two points 1m apart on the cable, the oscilloscope traces would be in phase. That is, the voltages would be the same, and changing the same amount in the same direction at all times.
     
  10. Feb 6, 2009 #9
    Im having trouble following this...

    Im trying to picture what the ordinary AC house-hold supply of 60Hz at wave-length of about 5 x 10^6 m actually looks like on the atomic/sub atomic level.

    I know that the 60hz means the free electrons of the copper atom are moving back and forth 60 times a second inside the wire.

    Its to my understanding that the electron flow inside the wire is very slow compared to the speed of the electromagnetic wave outside of the wire that is moving around light speed, and the speed of this wave is measured as voltage in units of volts and this wave is just a motion of particles in the sea of matter outside the wire.

    The current is the movement of electrons inside the wire measured in amps that are = to 6.241506×10^18 electrons moving past a point on the circuit in one second. The number 6.241506×10^18 is the number of electrons in the unit of measure called a coulomb.

    I don’t understand what the wavelength actually is in terms of atomic or sub atomic particles, Im not sure if its referring to the electromagnetic wave of particals out side the wire or if it is referring to something inside the wire, both or nether.

    Id like to be able to draw this out on paper and then be able draw a circle around one wavelength so I can visualize what a wave length is. I understand that is a distance between two points but what are those two points made out of and where are they located, inside the wire, outside the wire or both?
     
  11. Feb 6, 2009 #10

    berkeman

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    Close to true. The electrons are moving in the wire, but the only things outside of the wire are the electric and magnetic fields associated with the travelling wave. The Electric field is mostly between the 2 or 3 conductors of the transmission line, and the magnetic fields are encircling each wire. It is this oscillating travelling EM wave that drives the power down the transmission line.

    It may be too much of a stretch to relate the long wavelength of power transmission to things on the scale of the electron. Just as it is difficult to relate the wavelength of an ocean wave to the H2O molecules that comprise it.

    Here's a Google Images search on wavelength:

    http://images.google.com/images?hl=en&q=wavelength&gbv=2

    In the context of a transmission line, you usually draw the voltage versus position for a snapshot in time. If you animate it in time, you show the travelling voltage waveform going down the line from the source to wherever.

    I googled transmission line +animation, and got some good hits. Here's one from HP/Agilent which is very cool, but may confuse you more. I'll post it anyway in case others want to see a cool phasor representation of a transmission line:

    http://education.tm.agilent.com/index.cgi?CONTENT_ID=6 [Broken]

    Here are more traditional ones that may make more sense to you:

    http://users.encs.concordia.ca/~trueman/FIE.pdf

    http://www.ece.unb.ca/petersen/links/java/txlinesteadystate/

    And here's "Visualization and Animation of Electric Power Systems"

    http://wolfweb.unr.edu/~cevrenosoglu/misc/viz/visual.html [Broken]
     
    Last edited by a moderator: May 4, 2017
  12. Feb 7, 2009 #11

    Dale

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    Actually, it is a much shorter distance than than. For example, the drift velocity for a 20 A current in a 12 gauge copper wire is 0.4 mm/s (typical max current in residential wiring, see http://hyperphysics.phy-astr.gsu.edu/hbase/electric/miccur.html#c3). That would mean displacements less than 2 um over the duration of a quarter wavelength.


    Cyrus, as you noted the wavelength of residential 60 Hz electricity is huge, so you can consider all of the wires in a house to be at the same voltage at any given instant and ignore the wavelength. Just think that 60 times per second the all the electrons in the wire are pushed a couple of micrometers one direction and then a couple of micrometers the other direction. The electric repulsion between two neighboring electrons is so strong that when the generator pushes on one electron then that electron pushes on the next, which pushes on the next, etc. thus they all move in the same direction together. In that sense it is like a very incompressible fluid (voltage is like pressure and current is like flow, it is a pretty good analogy for many purposes).
     
    Last edited: Feb 7, 2009
  13. Feb 7, 2009 #12
    Thanks guys that info is really enlightening. Im trying to grasp the concept of these waves…

    Say I have a standard copper wire like in my house with AC 60hz at 5 x 10^6 m.

    60 times per second the all the electrons in the wire are pushed a couple of micrometers one direction and then a couple of micrometers the other direction.

    So like if the wire goes left to right and the electrons inside the wire are moving left to right a couple of micrometers 60 times a second, they are causing a wave outside the wire to push left when the electrons go left and push another wave right when the electrons go to the right?
     
  14. Feb 7, 2009 #13

    Dale

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    Almost. The way the math works out the waves go outwards from the wire rather than specifically left or right.
     
  15. Feb 7, 2009 #14
    How far do the waves go? Dose thier speed vary with the range of amps? Dose gravity affect them at all?
     
  16. Feb 7, 2009 #15

    Dale

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    Technically they go out to infinity, but they are not very powerful so they get pretty hard to detect pretty quickly.
    No, their speed is always c (light speed) regardless of the amperage.
    Yes. Gravity bends their path and redshifts their frequency.
     
  17. Feb 8, 2009 #16

    berkeman

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    Thanks for the correction, Dale. I remembered small numbers, but had never worked out anything way down at 60Hz. I was thinking that the currents would be pretty big in power distribution lines, but even if they are two orders of magnitude over house currents, that's still less than a mm.
     
  18. Feb 8, 2009 #17


    What do you mean “between the 2 or 3 conductors of the transmission line” ? I thought the whole line was the conductor because it has free electrons and is said to conduct electricity. I tried to look this up but stuff keeps saying copper is a conductor etc.

    If the electromagnetic waves are flying out in all directions equally according to the math then what way are the magnetic fields waves traveling that are “encircling” the wire?Are they going left and right? Just to the right? Are they to flying out in all directions?

    Another question…

    Say I have a standard copper wire like in my house with AC 60hz at 5 x 10^6 m.

    Is there any difference with fields or anything between a wire like this that’s strait and about 20 feet long and just looks like a strait wire kind of like this…

    - - - - - - --- - - - - - - -- - -- --- - -- -- -- - - -- -- -- -- - -- - - - -- - - - - - - -- - ----

    And a wire that’s been twisted in coils in the middle like this…

    ------------------------@@@@@@@----------------------------------------------

    Like its supposed to increase the voltage or something? Would doing this to a wire do anything at all to the fields or electrons or something???
     
  19. Feb 8, 2009 #18

    Dale

    Staff: Mentor

    Yeah, I was stunned when I first actually worked out how small the velocities are. I don't know about transmission lines. I am sure they carry a lot of current, but they are also very thick, so I don't know what the end result would be.
     
  20. May 29, 2009 #19
    The transformer next to your house is separating charge from your neutral to your hot wire 60 times a second. The hot wire becomes more positively charged than the neutral for half a cycle. Then as the cycle reverses, the hot wire becomes more negatively charged.

    Since they repel each other, the electrons will move a little bit as the transformer pumps the charge into one pair of ends of the wires. They'll move a little bit more if you plug something into your outlet, completing the circuit.
     
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