3 ms·

I’ve always wondered if you tried to run a current through a metal belt moving in the opposite direction of electron flow at a speed higher than the drift veloc

I’ve always wondered if you tried to run a current through a metal belt moving in the opposite direction of electron flow at a speed higher than the drift velocity if the circuit would complete? (For the sake of argument let’s says it’s not connected like a belt would be. )

feoren 3y ago
Put yourself in the frame of reference of the moving belt. An electric current is running through you, and also some other machinery around you is moving very slowly in the same direction as the current. So? Why should the movement of some background stuff affect the near-speed-of-light energy propagation passing through you?
- bilsbie 3y ago
  That was my first thought. But if it’s not connected like a belt it physically can’t replace any electrons it loses.
adolph 3y ago
Isn't current an instantiation of an electro-magnetic field and so the movement of the belt wouldn't matter? It all lights up at the same time. Considering a conveyer belt portion that is part of a circuit, doesn't the portion of the belt that is energized change as fast as the belt moves? https://physics.stackexchange.com/questions/707402/veritasium-electricity-videos-where-does-the-majority-of-energy-really-flow https://physics.stackexchange.com/questions/707402/veritasiu... https://www.reddit.com/r/engineering/comments/qxrsrp/the_big_misconception_about_electricity_veritasium/ https://www.reddit.com/r/engineering/comments/qxrsrp/the_big... https://www.youtube.com/watch?v=O-WCZ8PkrK0 https://www.youtube.com/watch?v=O-WCZ8PkrK0
tzs 3y ago
My first impression is that yes, the circuit would complete. Keep in mind that the metal has both negatively charged electrons which are reasonably free to move around within the metal and positively charged protons that are generally in the nuclei which are fairly fixed within the metal. If you have the metal belt moving so that the electrons are not actually moving (from the point of view of a stationary observer outside the belt) that observer would see the protons moving. You've still got, from the outside observer's point of view, a current. It just is now a proton current instead of an electron current.
Workaccount2 3y ago
Yes, because the circuit is an alignment of charges that creates a electric field. The fact that electrons drift along it is immaterial to the circuit functioning. For things to get weird you would need to have the belt moving at relativistic speeds, >80% the speed of light.
- rcxdude 3y ago
  It is very material: the movement of charge is necessary for electricity. In this case electrons are still moving into and out of the belt, even if the bulk is not moving in the direction of the flow of current.
calamari4065 3y ago
Yes. Electricity moves at the speed of light[0] and like light will be constant no matter your reference frame. [0] the speed of light in a given material and conditions. Generally it's a good fraction slower than light, but remember that light also moves slower through different materials.
- im3w1l 3y ago
  "the speed of light in a given material and conditions" is not constant in different reference frames. Only the vaccum speed of light is.
  - tsimionescu 3y ago
    Not sure why you're getting downvoted, this is an important point. The speed of light that is a constant is c. The actual (average) speed that light travels through a material is not a limit of any kind, and it is very possible for other particles to move through that medium faster than light. For example, Cherenkov radiation is high energy electrons moving faster than light through water (not faster than c). Of course, what actually happens is that photons always move with speed c, but the path they take through a medium is not straight - they "bump" into other particles, so it takes them longer to reach the end. Higher energy particles can have straighter paths (they "push bumps away"), so that even if their instantaneous speed is always lower than the photons', they take less total time to move through the material.
thereisnospork 3y ago
This experiment actually gets very feasible if we replace electrons with ions, and the metal carrier with (e.g.) an aqueous electrolyte in an electrochemical circuit. Something like splitting water in H2SO4 would be an easy starting point. This means our charges no longer move at relativistic speeds, and have very short mean free paths, therefore it is possible to flow water[0] against the electrical flow of ions at greater than the mean diffusion speed. My not overly confident understanding[1] is that this does in fact break the circuit and prevent the flow of current. Also worth noting, by choosing a colorful ion choice of ion it is possible to directly observe their formation and travel. You can also use electrons as your negative ion directly in liquid ammonia, forming a pretty deep blue solution. [0]Aqueous or other electrolyte. [1]My theoretical echem is a bit rusty, so ymmv.

feoren 3y ago

Put yourself in the frame of reference of the moving belt. An electric current is running through you, and also some other machinery around you is moving very slowly in the same direction as the current. So? Why should the movement of some background stuff affect the near-speed-of-light energy propagation passing through you?

bilsbie 3y ago
That was my first thought. But if it’s not connected like a belt it physically can’t replace any electrons it loses.

adolph 3y ago

Isn't current an instantiation of an electro-magnetic field and so the movement of the belt wouldn't matter? It all lights up at the same time. Considering a conveyer belt portion that is part of a circuit, doesn't the portion of the belt that is energized change as fast as the belt moves? https://physics.stackexchange.com/questions/707402/veritasium-electricity-videos-where-does-the-majority-of-energy-really-flow https://physics.stackexchange.com/questions/707402/veritasiu... https://www.reddit.com/r/engineering/comments/qxrsrp/the_big_misconception_about_electricity_veritasium/ https://www.reddit.com/r/engineering/comments/qxrsrp/the_big... https://www.youtube.com/watch?v=O-WCZ8PkrK0 https://www.youtube.com/watch?v=O-WCZ8PkrK0

tzs 3y ago

My first impression is that yes, the circuit would complete. Keep in mind that the metal has both negatively charged electrons which are reasonably free to move around within the metal and positively charged protons that are generally in the nuclei which are fairly fixed within the metal. If you have the metal belt moving so that the electrons are not actually moving (from the point of view of a stationary observer outside the belt) that observer would see the protons moving. You've still got, from the outside observer's point of view, a current. It just is now a proton current instead of an electron current.

Workaccount2 3y ago

Yes, because the circuit is an alignment of charges that creates a electric field. The fact that electrons drift along it is immaterial to the circuit functioning. For things to get weird you would need to have the belt moving at relativistic speeds, >80% the speed of light.

rcxdude 3y ago
It is very material: the movement of charge is necessary for electricity. In this case electrons are still moving into and out of the belt, even if the bulk is not moving in the direction of the flow of current.

calamari4065 3y ago

Yes. Electricity moves at the speed of light[0] and like light will be constant no matter your reference frame. [0] the speed of light in a given material and conditions. Generally it's a good fraction slower than light, but remember that light also moves slower through different materials.

im3w1l 3y ago
"the speed of light in a given material and conditions" is not constant in different reference frames. Only the vaccum speed of light is.
- tsimionescu 3y ago
  Not sure why you're getting downvoted, this is an important point. The speed of light that is a constant is c. The actual (average) speed that light travels through a material is not a limit of any kind, and it is very possible for other particles to move through that medium faster than light. For example, Cherenkov radiation is high energy electrons moving faster than light through water (not faster than c). Of course, what actually happens is that photons always move with speed c, but the path they take through a medium is not straight - they "bump" into other particles, so it takes them longer to reach the end. Higher energy particles can have straighter paths (they "push bumps away"), so that even if their instantaneous speed is always lower than the photons', they take less total time to move through the material.

thereisnospork 3y ago

This experiment actually gets very feasible if we replace electrons with ions, and the metal carrier with (e.g.) an aqueous electrolyte in an electrochemical circuit. Something like splitting water in H2SO4 would be an easy starting point. This means our charges no longer move at relativistic speeds, and have very short mean free paths, therefore it is possible to flow water[0] against the electrical flow of ions at greater than the mean diffusion speed. My not overly confident understanding[1] is that this does in fact break the circuit and prevent the flow of current. Also worth noting, by choosing a colorful ion choice of ion it is possible to directly observe their formation and travel. You can also use electrons as your negative ion directly in liquid ammonia, forming a pretty deep blue solution. [0]Aqueous or other electrolyte. [1]My theoretical echem is a bit rusty, so ymmv.