General > General Technical Chat
Same polarity but different direction of current flow. How annoying!
TimFox:
In the case of a transmission line, such as a small-diameter coaxial cable, it is useful to measure at a plane (perpendicular to the cable), where the voltage is defined locally between center and shield, and the current is defined as flowing in either direction along the wire through the plane. This avoids any discrepancies at high frequencies due to non-local measurements. The product of the voltage and current determines which way the (AC) power is flowing.
S. Petrukhin:
--- Quote from: helius on September 24, 2020, 07:31:25 am ---
--- Quote from: tkamiya on September 23, 2020, 05:54:05 am ---When we did understood electrons, we found out that electrons actually flow from negative to positive. So what you are observing is correct. To rectify this situation somewhat, explanation that "hole" (location of absence of electron) moves the same way current moves.
--- End quote ---
The hole is a real phenomena that only exists in p-type semiconductors. The wires in basic electric circuits definitely do not conduct by means of holes!
--- Quote from: tkamiya on September 23, 2020, 05:54:05 am ---BUT, there is nothing flowing from positive to negative.
--- End quote ---
Batteries and wires are human inventions, not fundamental physical objects. It is undesirable to define the latter for the convenience of the former.
In general, the conception that "electrons are moving like little corpuscles in a tube" is just naïve and misleading. Electrons do not even have a definite location and thus the idea that they are "flowing from negative to positive" is wrong. This wrong intuition gives rise to a host of other wrong ideas, like the idea that electrons "start out" from the negative terminal and must travel around the circuit before entering the positive terminal, so they must flow very quickly because current is equal in both branches from the moment the circuit is completed. Visualizing electrons flowing is the sign somebody doesn't understand electronics.
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There is a well-known physical experience: if a coil with a wire is spun around its axis, and abruptly stopped, an electric current will appear on the outputs. This suggests that there is some substance in the wire that has mass and inertia. People think of it as electrons.
tkamiya:
--- Quote from: helius on September 24, 2020, 07:31:25 am ---In general, the conception that "electrons are moving like little corpuscles in a tube" is just naïve and misleading. Electrons do not even have a definite location and thus the idea that they are "flowing from negative to positive" is wrong. This wrong intuition gives rise to a host of other wrong ideas, like the idea that electrons "start out" from the negative terminal and must travel around the circuit before entering the positive terminal, so they must flow very quickly because current is equal in both branches from the moment the circuit is completed. Visualizing electrons flowing is the sign somebody doesn't understand electronics.
--- End quote ---
It depends on how accurate the explanations has to be. If someone is asking which direction current flows and I were to answer in terms of electrons, taking so far as to get quantum mechanics involved will surely lose the audience. I'd settle for better understanding, rather than being exact and lose the conversation altogether. Yes, I understand the concept you are talking about and can explain it in that term. I actually took a course involving this exact manner in high school. The term used then was "like flowing this direction" when talking about transfer of free electrons, and it's successive transfers. Electrons not having defined location but is a probability is an idea of quantum mechanics. I'm not sure if we have to involve that in even semi-technical conversation.
ebastler:
--- Quote from: Berni on September 24, 2020, 08:09:04 am ---The reason the positive terminal is called the positive terminal because it is at a higher electrical potential than the negative terminal. But the flow of electrons is dictated by a difference of potentials, so as soon as you connect two different voltage potentials that starts pulling electrons along and you get current.
--- End quote ---
Thank you for the second post in a long thread that is actually on topic, i.e. addressing the OP's confusion. :-+
(newbrain was the first to explain it, in reply #4.)
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