3 ms·

Intuitive but wrong (and doggedly persistent) idea #1: "electric current is moving electrons". It is moving photons, exciting (largely) stationary electrons. I

Intuitive but wrong (and doggedly persistent) idea #1: "electric current is moving electrons". It is moving photons, exciting (largely) stationary electrons. I can't stress how crucial overcoming that misconception was when I was doing EE.

palunon 10y ago
Holy crap. It all make sense now. Thank you !
pitaj 10y ago
Ehhhhh. Not really. It is the rate of charge passing through a cross-section. That's how it's defined, and as an EE student, what you're saying made little-to-no sense to me.
- bandrami 10y ago
  And the boson that mediates "charge" is....?
  - wbeaty 10y ago
    Note that photons only travel along FO cable because of the charge polarization of the silica. This is a direct analog to 60Hz "electric power" traveling along a column of mobile charges in a long conductor. In both cases, the electrons wiggle back and forth, while the photons couple to them, and are guided along. But charge is not energy, in exactly the same way that amperes are not watts, and current is not EM energy-flow. Coulombs wiggle within the waveguide, while the Joules proceed continuously forward as propagating waves. The EM energy is in the form of propagating waves, while electric charge provides the medium: the waveguide.
  - pitaj 10y ago
    Photons don't mediate charge. The mediate the electric and magnetic fields.
    - bandrami 10y ago
      And the field that is quantified as "charge" is...?
      - pitaj 10y ago
        An electron? I don't know what you're getting at here. An electrostatic field is produced with strength in proportion to the charge. However, that is not the only way an electric field can exist. For instance, they can be produced by changing magnetic fields, and when these two fields interact in a way that they mutually generate one another, that's what we call an electromagnetic wave, or "photon." Photons don't mediate charge, they simply are the carrier for the information of a changing electric or magnetic field. It seems like you have a fundamental misunderstanding of how photons are produced, or what they do. At least in DC conditions, no photons are produced at all (since there is no changing magnetic or electric field), yet there is still current. Current is the movement of charge. Photons are irrelevant, besides being the messengers for the electric and magnetic fields, which still only applies if those fields are changing, as no information is changed otherwise, so no bozon is necessary. What you may be thinking of is in an AC case, where current is constantly changing as the electric field wave propagates down the transmission line. This does necessitate photons. But even then, the current is still the flow of charge, and oscillates between negative and positive.
k__ 10y ago
Is this why my EE prof once said, a metal cabel is like a fiber cabel, it trasfers EM energy but at a different wave length? This sounded like he went mad to me...
- dom0 10y ago
  But there is a reason why it sounds so confusing even to an advanced student -- even though EM radiation is at the heart of this science it is often surprisingly difficult to find correct and conclusive information on related topics. For example, finding answers to questions like "Why does absorption of EM waves in matter rise with lower wavelengths, but at the wavelengths of light matter starts to become more and more transparent again" isn't easy. But so are the involved phenomenons, after all.
- VLM 10y ago
  Think of the behavior of RF transmission lines. RF is after all just long wavelength light or EM waves. So obviously a piece of pipe is a circular waveguide and it works more or less like optical fiber. It helps if you know how optical fiber works, across a boundary with a big enough difference in speed of light in the material, you get total internal reflection and it bounces back in. Now people are pretty chill with circular waveguide as a transmission line, but there are numerous other schemes and eventually you end up with microstripline or twin-lead that TVs used to use or eventually one wire Goubau line. https://en.wikipedia.org/wiki/Single-wire_transmission_line https://en.wikipedia.org/wiki/Single-wire_transmission_line Once you're chill with a zillion small steps from circular waveguide to G-line, wait, G-line is what your prof said that initially sounded ridiculous, but its not so ridiculous after all, with some new perspective.
wbeaty 10y ago
Actually, it's electric wattage which is the moving photons, not electric current. Energy flow. Joules per second, same as with laser outputs. So, the electric companies are selling us 60Hz photons. But at the same time, the AC electricity just vibrates back and forth inside the wires, without any net forward motion. About the only accurate diagram of EM spectrum I've ever encountered was the one made by R. Oppenheimer and sold as a classroom poster by The Exploratorium in SF. At the bottom, below VLF radio, we find audio-freq phone lines, and below that, 60Hz power lines. "Electric power" is on the EM spectrum, down below radio waves. And yes, if we have a big enough antenna tower, then we can hook it up to a 60Hz dynamo, and spew 60Hz EM radiation out into space. Actually that concept was one of N. Tesla's great breakthroughs: hooking a steam-powered 50KHz alternator directly to an antenna, and broadcasting a silent carrier: CW. A couple years after his patents on this ran out, GE suddenly announced the "Alexanderson Alternator!" Finally making music/voice broadcasting possible! The public wondered how Alexanderson managed to come up with such an amazing idea. (If investors had bought Tesla stock, we'd have had AM radio ~20 years earlier. Tesla clearly grasped the concept that "radio" was the same thing as "electric power," just higher in frequency.) https://www.datavisualization.ch/wp-content/uploads/2009/07/electromagnetic_spectrum_01.jpg https://www.datavisualization.ch/wp-content/uploads/2009/07/...
- bandrami 10y ago
  I remember that poster! I actually got a copy from the Exploratorium...
notalaser 10y ago
It may be useful to understand where this error is coming from. Back when the theory of electrical current was developed, we had no good model of the atom. We had no idea about electrons, protons and neutrons, no idea about photons, quarks, nothing. Kirchoff developed his equations without knowing anything about electrons. When Ohm discovered his law, he knew nothing about electrons. Classical electromagnetism, in its entirety, is formulated without any knowledge of electrons (except with some of the late stuff that was developed in order to extend it to relativistic cases, but at that point we were already operating on "legacy code"). The modern idea of the atom, as we know it now, was developed more or less at the same time with classical electromagnetism; various theories about matter were being thrown around at the time, and for a long time, it was thought that electricity would be caused by some sort of charged fluid. Only beginning with the 1870s, at which time Maxwell was already revising his all-encompassing treaty, did the idea that it's all about particles really begin to take off. The electrical charges in the classic theory of electromagnetism are not electrons, nor ions, nor any other particles that we know of. They're ideal models of "something" that carries charge, but they do not model all the inherent behaviour of electrons (e.g. the electrical charges of classical electromagnetism do not have any magnetic moments, unlike real-life electrons). They are somewhat like the point particles in kinematics, in that they capture an essential feature (electrical charge) of an object while dispensing with other features that are not essential for the study of some (but not all!) phenomenons. It's ok to model electric current as "the flow of charge", as long as you don't give this model more physical meaning than it's due and attempt to equate the charges of classical electromagnetism with electrons. Certain phenomenons can be studied within this frame: for instance, the motion of an electron's motion through static electrical and magnetic fields is generally (low enough frequencies, strong enough magnetic fields etc.) OK to do while equating the electron with the charge carrier of classical electromagnetism. But back when the concept of electrical charge was elaborated, we knew nothing of electrons. The phenomenons gave enough clues for us to hypothesize that whatever "supports" electricity has some of the properties that "real" charge carriers have, but that's all there is to it.

palunon 10y ago

Holy crap. It all make sense now. Thank you !

pitaj 10y ago

Ehhhhh. Not really. It is the rate of charge passing through a cross-section. That's how it's defined, and as an EE student, what you're saying made little-to-no sense to me.

bandrami 10y ago
And the boson that mediates "charge" is....?
- wbeaty 10y ago
  Note that photons only travel along FO cable because of the charge polarization of the silica. This is a direct analog to 60Hz "electric power" traveling along a column of mobile charges in a long conductor. In both cases, the electrons wiggle back and forth, while the photons couple to them, and are guided along. But charge is not energy, in exactly the same way that amperes are not watts, and current is not EM energy-flow. Coulombs wiggle within the waveguide, while the Joules proceed continuously forward as propagating waves. The EM energy is in the form of propagating waves, while electric charge provides the medium: the waveguide.
- pitaj 10y ago
  Photons don't mediate charge. The mediate the electric and magnetic fields.
  - bandrami 10y ago
    And the field that is quantified as "charge" is...?
    - pitaj 10y ago
      An electron? I don't know what you're getting at here. An electrostatic field is produced with strength in proportion to the charge. However, that is not the only way an electric field can exist. For instance, they can be produced by changing magnetic fields, and when these two fields interact in a way that they mutually generate one another, that's what we call an electromagnetic wave, or "photon." Photons don't mediate charge, they simply are the carrier for the information of a changing electric or magnetic field. It seems like you have a fundamental misunderstanding of how photons are produced, or what they do. At least in DC conditions, no photons are produced at all (since there is no changing magnetic or electric field), yet there is still current. Current is the movement of charge. Photons are irrelevant, besides being the messengers for the electric and magnetic fields, which still only applies if those fields are changing, as no information is changed otherwise, so no bozon is necessary. What you may be thinking of is in an AC case, where current is constantly changing as the electric field wave propagates down the transmission line. This does necessitate photons. But even then, the current is still the flow of charge, and oscillates between negative and positive.

k__ 10y ago

Is this why my EE prof once said, a metal cabel is like a fiber cabel, it trasfers EM energy but at a different wave length? This sounded like he went mad to me...

dom0 10y ago
But there is a reason why it sounds so confusing even to an advanced student -- even though EM radiation is at the heart of this science it is often surprisingly difficult to find correct and conclusive information on related topics. For example, finding answers to questions like "Why does absorption of EM waves in matter rise with lower wavelengths, but at the wavelengths of light matter starts to become more and more transparent again" isn't easy. But so are the involved phenomenons, after all.
VLM 10y ago
Think of the behavior of RF transmission lines. RF is after all just long wavelength light or EM waves. So obviously a piece of pipe is a circular waveguide and it works more or less like optical fiber. It helps if you know how optical fiber works, across a boundary with a big enough difference in speed of light in the material, you get total internal reflection and it bounces back in. Now people are pretty chill with circular waveguide as a transmission line, but there are numerous other schemes and eventually you end up with microstripline or twin-lead that TVs used to use or eventually one wire Goubau line. https://en.wikipedia.org/wiki/Single-wire_transmission_line https://en.wikipedia.org/wiki/Single-wire_transmission_line Once you're chill with a zillion small steps from circular waveguide to G-line, wait, G-line is what your prof said that initially sounded ridiculous, but its not so ridiculous after all, with some new perspective.

wbeaty 10y ago

Actually, it's electric wattage which is the moving photons, not electric current. Energy flow. Joules per second, same as with laser outputs. So, the electric companies are selling us 60Hz photons. But at the same time, the AC electricity just vibrates back and forth inside the wires, without any net forward motion. About the only accurate diagram of EM spectrum I've ever encountered was the one made by R. Oppenheimer and sold as a classroom poster by The Exploratorium in SF. At the bottom, below VLF radio, we find audio-freq phone lines, and below that, 60Hz power lines. "Electric power" is on the EM spectrum, down below radio waves. And yes, if we have a big enough antenna tower, then we can hook it up to a 60Hz dynamo, and spew 60Hz EM radiation out into space. Actually that concept was one of N. Tesla's great breakthroughs: hooking a steam-powered 50KHz alternator directly to an antenna, and broadcasting a silent carrier: CW. A couple years after his patents on this ran out, GE suddenly announced the "Alexanderson Alternator!" Finally making music/voice broadcasting possible! The public wondered how Alexanderson managed to come up with such an amazing idea. (If investors had bought Tesla stock, we'd have had AM radio ~20 years earlier. Tesla clearly grasped the concept that "radio" was the same thing as "electric power," just higher in frequency.) https://www.datavisualization.ch/wp-content/uploads/2009/07/electromagnetic_spectrum_01.jpg https://www.datavisualization.ch/wp-content/uploads/2009/07/...

bandrami 10y ago
I remember that poster! I actually got a copy from the Exploratorium...

notalaser 10y ago

It may be useful to understand where this error is coming from. Back when the theory of electrical current was developed, we had no good model of the atom. We had no idea about electrons, protons and neutrons, no idea about photons, quarks, nothing. Kirchoff developed his equations without knowing anything about electrons. When Ohm discovered his law, he knew nothing about electrons. Classical electromagnetism, in its entirety, is formulated without any knowledge of electrons (except with some of the late stuff that was developed in order to extend it to relativistic cases, but at that point we were already operating on "legacy code"). The modern idea of the atom, as we know it now, was developed more or less at the same time with classical electromagnetism; various theories about matter were being thrown around at the time, and for a long time, it was thought that electricity would be caused by some sort of charged fluid. Only beginning with the 1870s, at which time Maxwell was already revising his all-encompassing treaty, did the idea that it's all about particles really begin to take off. The electrical charges in the classic theory of electromagnetism are not electrons, nor ions, nor any other particles that we know of. They're ideal models of "something" that carries charge, but they do not model all the inherent behaviour of electrons (e.g. the electrical charges of classical electromagnetism do not have any magnetic moments, unlike real-life electrons). They are somewhat like the point particles in kinematics, in that they capture an essential feature (electrical charge) of an object while dispensing with other features that are not essential for the study of some (but not all!) phenomenons. It's ok to model electric current as "the flow of charge", as long as you don't give this model more physical meaning than it's due and attempt to equate the charges of classical electromagnetism with electrons. Certain phenomenons can be studied within this frame: for instance, the motion of an electron's motion through static electrical and magnetic fields is generally (low enough frequencies, strong enough magnetic fields etc.) OK to do while equating the electron with the charge carrier of classical electromagnetism. But back when the concept of electrical charge was elaborated, we knew nothing of electrons. The phenomenons gave enough clues for us to hypothesize that whatever "supports" electricity has some of the properties that "real" charge carriers have, but that's all there is to it.