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A statement about a diode conducting current in only one direction is fine because it is intrinsically applicable to whatever convention you are using. If your convention means that the (ideal) diode can conduct -10 mA, then the diode cannot conduct any positive-valued current. If your convention means that the diode can conduct +10 mA, then the diode cannot conduct any negative-valued current.
Conventional vs Electron flow
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I agree, the convention definitely complicated stuff since the equations were all written for the opposite convention. I personally would never use it. I think it would be better if we wanted to model electrons, we used a negative current value in their direction. I don’t get what is “wrong” about that and why a new electron convention was even created. If electrons are negative charges and current is the movement of charges the movement of electrons is negative current. This makes sense and falls in line with the statement that positive current is in the direction of positive charge. I think the reason the new convention was invented is because we are following the historical thinking of signed quantities as you said. To me it doesn’t make much sense to always think of current as positive. But we do this in everything. A diode is described as restricting current in one direction. The more correct and descriptive statement is to say a diode restricts positive current in one direction. Since we have essentially replaced the word current, with positive current, im sure those who wanted to model electrons thought using the negative value would be awkward. They could just state current is in the direction of electrons (thus meaning positive current) and it seemed “better” I guess. In my opinion, the other convention does nothing better but it feels forced to be that way since we have made the word current out to mean positive unless otherwise specified.
I just saw this after I posted my other response, so I apologize for including that statement again. I don’t see how this is true. Using conventional current and a forward biased diode, it will conduct a positive current in the direction of the diode arrow, or you could write is as conducting a negative current against the arrow. As you have stated earlier, a positive current one way and negative current the other way are not different conventions. Therefore, the diode could conduct current in either direction but the value in one direction would be positive and the value in the other would be negative.
It doesn't matter as there is little confusion in actual practice. If you truly are worried about electrons you are probably dealing with device physics. In that case you should have no confusion in actual practice because physical charge carrier movements are the least of your worries.
Agreed, I have seen in practice that this stuff doesn’t come up because everyone knows what each other is talking about. However, I don’t think I am in line with knowing what these common statements mean. It seems like when doing math solving circuits on paper, we can solve for currents and get negative values and no one is confused. We could even point the arrow out of the - terminal and get a negative value in a simple circuit and no one would say that the answer is wrong. However, if we were in a lab and I asked you which way the current went, you would give me the value of positive current. It seems like in practice, when we talk about current we are referencing positive current. When someone says current goes in the opposite direction of electrons, it’s because they are inferring positive current. However, if someone responded to them and said well technically current doesn’t always mean that it is opposite of electrons, if it is negative than it is in the direction of electrons. And all of the conversations would be staying within conventional current. In other words conventional current doesn’t say that a negative value for current is wrong or reporting back the current with a negative value is wrong, but rather WITHIN conventional current, we tend to talk about the positive version of conventional current similar to the way we do when talking about velocity. Is that correct?
In 'real' life people worry, think and have long meetings about 'forces' not current direction calculations when the physical movement of charge matters. For example on an X sized wafer I see dose variation patterns after a maintenance operation that exceed process specifications during a quality test. Obviously the direction of current and calculations using those current conventions didn't change but something (x force, more or less) that changed the characteristics of charge interaction across the wafer did. Time and effort is spend translating test results into possible physical, electrical and/or process adjustments that could cause the generation of X pattern.
Okay, I am not sure exactly the process you are referring to but I see your point. So in practice when you talk about current, why is it that we use the - sign to indicate direction. We say a negative current means current goes the other way. In that case it seems like positive is our default to talk about. Because we could also say positive current means current (negative) goes the other way and in that case taking about negative current would be our default. So it is my understanding in practice when we say the word current we mean positive current (conventional). And this tendency has nothing to do with the debate about which convention to use, as it doesn’t have anything to do with how we solve problems but rather the way we speak? I believe that even those who use electron flow, when they solve for a negative value they say current goes the other way too, it’s just that their positive current is different from ours.
Process would be the exact set of physical material science parameters needed for the end result (recipe) over a period of time. Most of the time we use the - sign to indicate direction of force, pushing or pulling, charging or discharging relative from some point while the exact positive/negative nature of the physical current is irreverent to the force equation in a problem solving investigation.
Okay, while I somewhat see your point this seems like some sort of ic design or other material science involves field that I just don’t have any knowledge about yet. I’ll just propose a circuits 101 lab type experience so that we can both relate. Let’s say we were lab partners and had some complicated resistor network and we want to measure the value for the current through one of the resistors. We’re not sure which way the positive current flows for the resistor so we just put in the ammeter leads arbitrarily and get a negative value on the display. Then someone else in the class says okay that’s fine, that just means current goes the other way, current can’t be negative unless you’re breaking convention. To that I reply, current is just fine negative but typically when we’re in the lab having a conversation we’re interested in the direction of positive current, there’s nothing wrong with the negative current but when you say that it means current is in the other direction what you’re actually saying is that positive current is in the other direction. Who would be speaking correctly? Me or the other person.
I apologize that this is not a very workplace- like scenario, but that is because professional engineers have a common understanding that I am trying to figure out by using this hypothetical scenario. I hope my question is clear.
The phrase "negative current against the arrow" is nonsensical. The arrow's sole purpose is to define the direction associated with a positive value of the associated quantity. A positive value (of whatever) is in the direction of the arrow, while a negative direction (of whatever) is in the direction opposite the arrow. It doesn't matter if we are talking about current, water flow, magnetic field, or whatever.
For any given analysis, you must choose what a positive value in the direction of the arrow means. If we are talking about electrical current in a circuit, then once you draw an arrow next to a diode to indicate the current through that diode, the value only take on non-zero values of one polarity (assuming an ideal diode). That is all that is meant by the statement that current flows only one direction in a diode.
The fact that Bob can take his copy of the schematic and assign the reference direction the other way or use a different convention and come up with a positive number while Sue can take her copy and do something different and come up with a negative number does not, in any way shape of form, qualify as the current in that diode being able to flow in both directions. No matter how you choose to describe the flow of current in that diode, current will flow in only one direction according to that description.
The ammeter (which we will assume is a DC ammeter) has a reference direction that is indicated by the polarity of the leads which defines the meaning of the polarity of the reading. In most ammeters, the current reads a positive value when net charge flowing through the ammeter is from the positive lead to the negative lead. If you get a negative reading, that means that net charge is flowing in the other direction. That can occur either because positively charged carriers are physically flowing the other direction, or negatively charged carries are physically flowing in the same direction. The meter cannot tell the difference because, in either case, net charge is flowing from the negative lead to the positive lead. As has been mentioned over and over again, a phrase like "net charge" always means a positive quantity. Humans think in terms of positive quantities. Our languages have evolved such that when we deal with signed quantities the reference always refers to positive values.
Okay, so the way I am reading this statement is yes “current” which is the flow of charge as we know can only flow in one direction of a diode. Meaning that whatever the current is caused by, if those charges flipped direction the diode would not be able to conduct current anymore. What I meant to say but worse very poorly is that the diode can only conduct current in one direction but that entails that you can represent the conducting current in two ways (Bob vs sue In your example above). Let me know if this is understood correctly from your statement.
What I was saying is you can’t just say a diode isn’t conducting because your reference arrow points against the arrow of the diode. If that reference arrow comes out to be a negative value than that means you have a corresponding positive arrow going in the same arrow direction as the diode and therefore we know it’s conducting.
We know the diode cannot conduct an equivalent Current in both directions (let’s say 3A one way and 3A the other way) but it can be represented in two ways (3A one way and -3A the other way)
Okay, I completely agree with your explanation of the ammeter as long as the flow of net charge means positive like you say. I am just having a hard time thinking that any word always means positive unless otherwise specified, I wish languages were more specific. I kind of wish our language had adapted to always specifically say positive or negative. Even my circuits book says that by convention current moves opposite to electrons but then says you can represent a conventional current as positive one way or negative the other. Explanations like that just don’t make sense unless you know that when the author says current they are talking about positive. I just feel like a first time introduction in a book should spexify that any unspecified quantity refers to the positive version of that quantity
Actually, you probably don't want languages to be more specific and require something like that. Think of a typical legal document and how it is written. That "legalese" is almost entirely due to trying to express things in a way in which there is only one way to interpret them -- and even so the courts are always having to decide between conflicting interpretations. But these are the exceptions. Humans and our languages have developed the way they have because the human mind has an extraordinary ability to extract the proper and intended meaning from an extremely ambiguous phrase using a variety of cues that we are almost never fully aware of. If we didn't have this ability, then even the simplest concepts would become impossibly cumbersome to communicate. For instance, if I say, "Don't cross on a yellow," chances are overwhelming that you will understand what I am trying to tell you even with no context whatsoever.
I just looked in a few of my texts and they all are very explicit about this. As just one example, Chapter 1 of Nilsson and Riedel, "Electric Circuits", 9th Ed, shows a two terminal device with a reference voltage, v, shown with terminal 1 positive and terminal 2 negative and a reference current, i, drawn with an arrow going into terminal 1. It then states, "The interpretation of these references given positive and negative numerical values of v and i is summarized in Table 1.4. This table then says, for positive i, that it means either "positive charge is flowing from terminal 1 to terminal 2" or "negative charge flowing from terminal 2 to terminal 1". It has similar definitions for the other possibilities.
Yes, I absolutely love the way Nilsson and Riedel explains it but for some reason most texts don’t do it that way. Would you mind sharing one of the other examples? Also, in that Nilsson and Riedel text they never say anything like “conventional current is opposite of the flow of electrons” or if you get a negative than current goes the other way. They simply state you have a positive current this is what it means, you have a negative current this is what it means, all of it is conventional current (they don’t say that part). I am talking about Sadiku and Alexander, I’ll link a screenshot if you want me to talk about it. Also, I agree what you are saying, but at the beginning of learning something I feel like it needs to be explicit. “Conventional current moves opposite to electrons” well obviously the author means in this case the current is positive because it hasn’t been specified otherwise. But what if a student reads that and thinks anytime they point their current arrow in the direction of the electrons they are doing something “wrong”? They might think that to give someone the direction of positive current whenever they request current, is because talking about negative current is wrong, rather than it just being a figment if our language to have a signed quantity be positive by default. This is kind of where I was at before I realized there was a hidden positive in front of these terms, which makes sense if you think about how we talk about velocity, displacement, etc. I just didn’t think it made as much sense to apply those same semantics to electric current
Correct.
Of course you can't say whether a diode is conducting or not just because of the direction you chose to draw an arrow on the schematic. The circuit neither knows nor cares about what direction you happened to draw some lines on a piece of paper (or the modern display equivalent).
Reference arrows do not come out to be negative. A reference arrow is a reference arrow and, once defined, does not change unless they are redefined (which is should usually involve starting from scratch as if you had never defined it before). The reference arrow is static and unchanging. It's purpose is to define the interpretation of positive and negative values by illustrating the intended meaning of the value when it is positive.
I'm not going to go through my library and give you every example from every text, so this is the last one.
Cunningham and Stuller, "Circuit Analysis", 2ed
"A current i of one ampere in the direction of the arrow will cause a net positive charge of one coulomb (C) per second to pass through the surface in the direction of the arrow." It then proceeds to show that this is equivalent to negative charges flowing through the area in the other direction.
I also have texts that do this poorly and are inconsistent with themselves, including specifying a positive charge for the charge on an electron, most likely because they wanted to then take the reciprocal to get the number of electrons the correspond to a charge having a magnitude of one coulomb. There is absolutely no shortage of poorly written texts -- remember, the authors of most texts have little to no real world experience.[/QUOTE]
EDIT: Fixed the BB tags.
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Yeah I guess this is one of those things that really comes down to understanding inherently what the word means. This is a case where the word means any current. More specifically, any current which a diode conducts in one direction will not be conducted in the other direction. And like you said this doesn’t just mean flipping our arrow and changing the sign. It means flipping the arrow withOUT changing the sign. And yes what I meant about the reference arrow was that if you write a reference arrow down and solve and get a negative value based on that reference. I believe this is always okay to do?
Yeah that’s a pretty good explanation as well. I will attach the exact explanation of the one I was told to use later on tomorrow. That is a fair point that a lot of times error come from the lack of practical experience. However for something like this which seems to be rooted in theory, you would think the authors would write in a very specific manner. I enjoy your responses on here because I can really understand what you are getting at from the details that you share and explain what you mean when you type a word. Many people in general but including text authors seem to assume certain words mean certain things which eventually can be fine but at the beginning makes it confusing. This was my point earlier about defining current without using the words positive or negative. I don’t think we should be introducing the concept of current as saying it moves in the direction of positive charge. For an experience person this is easily discernible as you said signed quantities are just typically referenced as positive and only written as negative when needed to be specified. But for a beginner how are they supposed to know then what to do if they get a negative current if it is defined so vaguely. The statements current moves in the direction of positive charge and positive current moves in the direction of positive charge do not inherently mean the same thing. They will only be equivalent if in the first one you know that current is specifying positive, which some beginners may not know
I must say, It's not about you. Countless people have advanced far beyond this point without a tiny fraction of the angst seen here.
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